In 1994 an Ethiopian member of a research team led by American palaeanthropologist Tim White discovered human fossils estimated to be about 4.4 million year’s old. White and his colleagues gave their discovery the name Ardipithecus ramidus. Ramid means ‘root’ in the Afar language of Ethiopia and refers to the closeness of this new species to the roots of humanity. At the time of discovery, the genus Australopithecus was scientifically well established. White devised the genus name Ardipithecus to distinguish this new species from other Australopiths because its fossils had a very ancient combination of apelike and humanlike traits. More recent finds indicate that this species may have lived as early as 5.8 million to 5.2 million years ago.
The teeth of Ardipithecus ramidus had a thin outer layer of enamel, - a trait also seen in the African apes but not in other australopith species or older fossil apes. This trait suggests a close relationship with an ancestor of the African apes. In addition, the skeleton shows strong similarities to that of a chimpanzee but has slightly reduced canine teeth and adaptations for Bipedalism.
In 1965 a research team from Harvard University discovered a single arm bone of an early human at the site of Kanapoi in northern Kenya. The researchers estimated this bone to be four million years old, but could not identify the species to which it belonged or return at the time to look for related fossils. It was not until 1994 that a research team, led by British-born Kenyan paleoanthropologist Meave Leakey, found numerous teeth and fragments of bone at the site that could be linked to the previously discovered fossil. Leakey and her colleagues determined that the fossils were those of the very primitive species of australopith, which was given the name Australopithecus anamensis. Researchers have since found other A. anamensis fossils at nearby sites, dating between about 4.2 million and 3.9 million years old. The skull of this species appears apelike, while its enlarged tibia (lower leg bone) indicates that it supported its full body weight on one leg at a time, as in regular bipedal walking
Australopithecus anamensis was quite similar to another, much better - known species, A. afarensis, a gracile australopith that thrived in eastern Africa between about 3.9 million and three million years ago. The most celebrated fossil of this species, known as Lucy, is a partial skeleton of a female discovered by American paleoanthropologist Donald Johanson in 1974 at Hadar, Ethiopia. Lucy lived 3.2 million years ago. Scientists have identified several hundred fossils of A. afarensis from Hadar, including a collection representing at least 13 individuals of both sexes and various ages, all from a single site.
Researchers working in northern Tanzania have also found fossilized bones of A. afarensis at Laetoli. This site, dated at 3.6 million years old, is best known for its spectacular trails of bipedal human footprints. Preserved in hardened volcanic ash, these footprints were discovered in 1978 by a research team led by British paleoanthropologist Mary Leakey. They provide irrefutable evidence that Australopiths regularly walked bipedally.
Paleoanthropologists have debated interpretations of the characteristics of A. afarensis and its place in the human family tree. One controversy centres on the Laetoli footprints, which some scientists believe show that the foot anatomy and gait of A. afarensis did not exactly match those of the modern humans. This observation may indicate that early Australopiths did not live primarily on the ground or at least spent a significant amount of time in the trees. The skeleton of Lucy also indicates that A. afarensis had longer, more powerful arms than most later human species, suggesting that this species was adept at climbing trees. Another controversy relates to the scientific classification of the A. afarensis fossils, compared with Lucy, who stood only 1.1 m. (3.5 ft.) tall, other fossils identified as A. afarensis from Hadar and Laetoli came from individuals who stood up to 1.5 m. (5 ft.) tall. This great difference in size leads some scientists to suggest that the entire set of fossils now classified as A. afarensis represents two species. Most scientists, however, believe the fossils represent one highly dimorphic species, - that is, a species that has two distinct forms (in this case, two sizes). Supporters of this view may note that both large (presumably male) and small (presumably female) adults occur together in one site at Hadar.
A third controversy arises from the claim that A. afarensis was the common ancestor of both later Australopiths and the modern human genus, Homo. While this idea remains a strong possibility, the similarity between this and another australopith species - one from southern Africa, named Australopithecus africanus - makes it difficult to decide which of the two species led to the genus Homo.
Australopithecus africanus thrived in the Transvaal region of what is now South Africa between about 3.3 million and 2.5 million years ago. Australian-born anatomist Raymond Dart discovered this species - the first known australopith - in 1924 at Taung, South Africa. The specimen that of a young child, became known as the Taung Child. For decades after this discovery, almost no one in the scientific community believed Dart’s claim that the skull came from an ancestral human. In the late 1930's teams led by Scottish-born South African paleontologist Robert Broom unearthed many more
A. africanus skulls and other bones from the Transvaal site of Sterkfontein.
A. africanus generally had a more globular braincase and less primitive-looking face and teeth than did A. afarensis. Thus, some scientists consider the southern species of early australopith to be a likely ancestor of the genus Homo. According to other scientists, however, certain heavily built facial and cranial features of A. africanus from Sterkfontein identify it as an ancestor of the robust Australopiths that lived later in the same region. In 1998 a research team led by South African paleoanthropologist Ronald Clarke discovered an almost complete early australopith skeleton at Sterkfontein. This important find may resolve some of the questions about where A. africanus fits in the story of human evolution.
Working in the Lake Turkana’s region of northern Kenya, a research team led by paleontologist in which Meave Leakey uncovered 1999 a cranium and other bone remains of an early human that showed a mixture of features unseen in previous discoveries of early human fossils. The remains were estimated to be 3.5 million years old, and the cranium’s small brain and earhole was similar to those of the earliest humans. Its cheekbone, however, joined the rest of the face in a forward position, and the region beneath the nose opening was flat. These are traits found in later human fossils from around two million years ago, typically those classified in the genus Homo. Noting this unusual combination of traits, researchers named a new genus and species, Kenyanthropus platy ops, or ‘flat-faced human from Kenya.’ Before this discovery, it seemed that only a single early human species, Australopithecus afarensis, lived in East Africa between four million and three million years ago. Yet Kenyanthropus indicates that a diversity of species, including a more humanlike lineage than A. afarensis, lived in this period, just as in most other eras in human prehistory.
The human fossil record is poorly known between three million and two million years ago, which make recent finds from the site of Bouri, Ethiopia, particularly important. From 1996 to 1998, a research team led by Ethiopian paleontologist Berhane Asfaw and American paleontologist Tim White found the skull and other skeletal remains of an early human specimen about 2.5 million years old. The researchers named it Australopithecus garhi; the word garhi means ‘surprise’ in the Afar language. The specimen is unique in having large incisors and molars in combination with an elongated forearm and thighbone. Its powerful arm bones suggest a tree - living ancestry, but its longer legs indicate the ability to walk upright on the ground. Fossils of A. garhi are associated with some of the oldest known stone tools, along with animal bones that were cut and cracked with tools. It is possible, then, that this species was among the first to make the transition to stone toolmaking and to eating meat and bone marrow from large animals.
By 2.7 million years ago the later, robust Australopiths had evolved. These species had what scientists refer to as megadont cheek teeth - wide molars and premolars coated with thick enamel. Their incisors, by contrast, were small. The robusts also had an expanded, flattened, and more vertical face than did gracile Australopiths. This face shape helped to absorb the stresses of strong chewing. On the top of the head, robust Australopiths had a sagittal crest (ridge of bone along the top of the skull from front to back) to which thick jaw muscles attached. The zygomatic arches (which extend back from the cheek bones to the ears), curved out wide from the side of the face and cranium, forming very large openings for the massive chewing muscles to pass through near their attachment to the lower jaw. Together, these traits indicate that the robust Australopiths chewed their food powerfully and for long periods.
Other ancient animal species that specialized in eating plants, such as some types of wild pigs, had similar adaptations in their facial, dental, and cranial anatomy. Thus, scientists think that the robust Australopiths had a diet consisting partly of tough, fibrous plant foods, such as seed pods and underground tubers. Analyses of microscopic wear on the teeth of some robust australopith specimens appear to support the idea of a vegetarian diet, although chemical studies of fossils suggest that the southern robust species may also have eaten meat.
Scientists originally used the word robust to refer to the late Australopiths out of the belief that they had much larger bodies than did the early, gracile Australopiths. However, further research has revealed that the robust Australopiths stood about the same height and weighed roughly the same amount as Australopithecus afarensis and A. africanus.
The earliest known robust species, Australopithecus aethiopicus, lived in eastern Africa by 2.7 million years ago. In 1985 at West Turkana, Kenya, American paleoanthropologist Alan Walker discovered a 2.5-million-year-old fossil skull that helped to define this species. It became known as the ‘black skull’ because of the colour it had absorbed from minerals in the ground. The skull had a tall sagittal crest toward the back of its cranium and a face that projected far outward from the forehead. A. aethiopicus shared some primitive features with A. afarensis, - that is, features that originated in the earlier East African australopith. This may indicate that
A. aethiopicus evolved from A. afarensis.
Australopithecus boisei, the other well-known East African robust australopith, lived over a long period, between about 2.3 million and 1.2 million years ago. In 1959 Mary Leakey discovered the original fossil of this species - a nearly complete skull - at the site of Olduvai Gorge in Tanzania. Kenyan-born paleoanthropologist Louis Leakey, husband of Mary, originally named the new species Zinjanthropus boisei (Zinjanthropus translates as ‘East African man’). This skull - dating from 1.8 million years ago - has the most specialized features of all the robust species. It could withstand extreme chewing forces, and molars four times the size of those in modern humans. Since the discovery of Zinjanthropus, now recognized as an australopith, scientists have found many A. boisei fossils in Tanzania, Kenya, and Ethiopia.
The southern robust species, called Australopithecus robustus, lived between about 1.8 million and 1.3 million years ago in Transvaal, the same region that was home to A. africanus. In 1938 Robert Broom, who had found many A. africanus fossils, bought a fossil jaw and molar that looked distinctly different from those in A. africanus. After finding the site of Kromdraai, from which the fossil had come, Broom collected many more bones and teeth that together convinced him to name a new species, which he called Paranthropus robustus (Paranthropus meaning ‘beside man’). Later scientists dated this skull at about 1.5 million years old. In the late 1940's and 1950 Broom discovered many more fossils of this species at the Transvaal site of Swartkrans.
Many scientists believe that robust Australopiths represent a distinct evolutionary group of early humans because these species share features associated with heavy chewing. According to this view, Australopithecus aethiopicus diverged from other Australopiths and later produced A. boisei and A. robustus. Paleoanthropologists who strongly support this view think that the robusts should be classified in the genus Paranthropus, the original name given to the southern species. Thus, these three species are sometimes called,
P. aethiopicus, P. boisei, and P. robustus.
Other paleoanthropologists believe that the eastern robust species, A. aethiopicus and A. boisei, may have evolved from an early australopith of the same region, perhaps A. afarensis. According to this view, A. africanus gave rise only to the southern species,
A. robustus. Scientists refer to such a case - in which two or more independent species evolve similar characteristics in different places or at different times, - as parallel evolution. If parallel evolution occurred in Australopiths, the robust species would make up two separate branches of the human family tree.
The last robust Australopiths died out about 1.2 million years ago. At about this time, climate patterns around the world entered a period of fluctuation, and these changes may have reduced the food supply on which robusts depended. Interaction with larger-brained members of the genus Homo, such as Homo erectus, may also have contributed to the decline of late Australopiths, although no compelling evidence exists of such direct contact. Competition with several other species of plant-eating monkeys and pigs, which thrived in Africa at the time, may have been an even more important factor. Nevertheless, the reasons why the robust Australopiths became extinct after flourishing for such a long time are not yet known for sure.
Scientists have several ideas about why Australopiths first split from the apes, initiating the course of human evolution. Nearly all hypotheses suggest that environmental change was an important factor, specifically in influencing the evolution of Bipedalism. Some well-established ideas about why humans first evolved include (1) the savanna hypothesis, (2) the woodland-mosaic hypothesis, and (3) the variability hypothesis.
The global climate cooled and became drier between eight million and five million years ago, near the end of the Miocene Epoch. According to the savanna hypothesis, this climate change broke up and reduced the area of African forests. As the forests shrunk, an ape population in eastern Africa became separated from other populations of apes in the more heavily forested areas of western Africa. The eastern population had to adapt to its drier environment, which contained larger areas of grassy savanna.
The expansion of dry terrain favoured the evolution of terrestrial living, and made it more difficult to survive by living in trees. Terrestrial apes might have formed large social groups in order to improve their ability to find and collect food and to fend off predators - activities that also may have required the ability to communicate well. The challenges of savanna life might also have promoted the rise of tool use, for purposes such as scavenging meat from the kills of predators. These important evolutionary changes would have depended on increased mental abilities and, therefore, may have correlated with the development of larger brains in early humans.
Critics of the savanna hypothesis argue against it on several grounds, but particularly for two reasons. First, discoveries by a French scientific team of australopith fossils in Chad, in Central Africa, suggest that the environments of East Africa may not have been fully separated from those farther west. Second, recent research suggests that open savannas were not prominent in Africa until sometime after two million years ago
Criticism of the savanna hypothesis has spawned alternative ideas about early human evolution. The woodland-mosaic hypothesis proposes that the early Australopiths evolved in patchily wooded areas - a mosaic of woodland and grassland - that offered opportunities for feeding both on the ground and in the trees, and that ground feeding favoured Bipedalism.
The variability hypothesis suggests that early Australopiths experienced many changes in environment and ended up living in a range of habitats, including forests, open-canopy woodlands, and savannas. In response, their populations became adapted to a variety of surroundings. Scientists have found that this range of habitats existed at the time when the early Australopiths evolved. So the development of new anatomical characteristics, - particularly Bipedalism - combined with an ability to climb trees, may have given early humans the versatility to live in a variety of habitats.
Scientists also have many ideas about which benefits of Bipedalism may have influenced its evolution. Ideas about the benefits of regular Bipedalism include that it freed the hands, making it easier to carry food and tools; allowed early humans to see over tall grass to watch for predators; reduced vulnerability of the body and too hot of the sun, provided an increased exposure to cooling winds; improved the ability to hunt or use weapons, which became easier with an upright posture; and made extensive feeding from bushes and low branches easier than it would have been for a quadruped. Scientists do not overwhelmingly support any one of these ideas. Recent studies of chimpanzees suggest, though, that the ability to feed more easily might have particular relevance. Chimps perform an action on two legs most often when they feed from the ground on the leaves and fruits of bushes and low branches. Chimps cannot, however, walk in this way over long distances.
Bipedalism in early humans would have enabled them to travel efficiently over long distances, giving them an advantage over quadrupedal apes in moving across barren open terrain between groves of trees. In addition, the earliest humans continued to have the advantage from their ape ancestry of being able to escape into the trees to avoid predators. The benefits of both Bipedalism and agility in the trees may explain the unique anatomy of Australopiths. Their long, powerful arms and curved fingers probably made them good climbers, while their pelvis and lower limb structure were reshaped for upright walking people belong to the genus Homo, which first evolved at least 2.3 million to 2.5 million years ago. The earliest members of this genus differed from the Australopiths in at least one important respect - they had larger brains than did their predecessors.
The evolution of the modern human genus can be divided roughly into three periods: during an early stage, an intermediate period and late. Species of early Homo resembled gracile Australopiths in many ways. Some early Homo species lived until possibly 1.6 million years ago. The period of middle Homo began perhaps between two million and 1.8 million years ago, overlapping with the end of early Homo. Species of middle Homo evolved an anatomy much more similar to that of modern humans but had comparatively small brains. The transition from middle to late Homo probably occurred sometime around 200,000 years ago. Species of late Homo evolved large and complex brains and eventually language. Culture also became an increasingly important part of human life during the most recent period of evolution.
The origin of the genus Homo has long intrigued paleoanthropologists and prompted much debate. One of several known species of Australopiths, or one not yet discovered, could have caused the first species of Homo. Scientists also do not know exactly what factors favoured the evolution of a larger and more complex brain - the defining physical trait of modern humans.
Louis Leakey originally argued that the origin of Homo related directly to the development of toolmaking, - specifically, the making of stone tools. Toolmaking requires certain mental skills and fine hand manipulation that may exist only in members of our own genus. The name Homo habilis (meaning ‘repairer’) refer directly to the making and use of tools
However, several species of Australopiths lived just when early Homo, making it unclear which species produced the earliest stone tools. Recent studies of australopith hand bones have suggested that at least a robust species, Australopithecus robustus, could have made tools. In addition, during the 1960's and 1970's researchers first observed that some nonhuman primates, such as chimpanzees, make and use tools, suggesting that Australopiths and the apes that preceded them probably also made some kinds of tools.
Scientists began to notice a high degree of variability in body size as they discovered more early Homo fossils. This could have indicated that H. habilis had a large amount of sexual dimorphism. For instance, the Olduvai female skeleton was dwarfed in comparison with other fossils, - exemplified by a sizable early Homo cranium from East Turkana in northern Kenya. However, the differences in size exceeded those expected between males and females of the same species, and this finding later helped convince scientists that another species of early Homo had lived in eastern Africa.
This second species of early Homo was given the name Homo rudolfensis, after Lake Rudolf (now Lake Turkana). The best - known fossils of H. rudolfensis come from the area surrounding this lake and date from about 1.9 million years ago. Paleoanthropologists have not determined the entire time range during which H. rudolfensis may have lived.
This species had a larger face and body than did H. habilis. The cranial capacity of H. rudolfensis averaged about 750 cu cm
(46 cu. in.). Scientists need more evidence to know whether the brain of H. rudolfensis in relation to its body size was larger than that proportion in H. habilis. A larger brain-to-body-size, and ratio can indicate increased mental abilities. H. rudolfensis also had large teeth, approaching the size of those in robust Australopiths. The discovery of even a partial fossil skeleton would reveal whether this larger form of early Homo had apelike or more modern body proportions. Scientists have found several modern-looking thighbones that date from between two million and 1.8 million years ago and may belong to H. rudolfensis. These bones suggest a body size of 1.5 m. (5 ft.) and 52 kg. (114 lb.).
By about 1.9 million years ago, the period of middle Homo had begun in Africa. Until recently, paleoanthropologists recognized one species in this period, Homo erectus. Many now recognize three species of middle Homo: H. ergaster, H. erectus, and H. heidelbergensis. However, some still think H. ergaster is an early African form of H. erectus, or that H. heidelbergensis is a late form of the H. erectus.
The skulls and teeth of early African populations of middle Homo differed subtly from those of later H. erectus populations from China and the island of Java in Indonesia. H. ergaster makes a better candidate for an ancestor of the modern human line because Asian H. erectus has some specialized features not seen in some later humans, including our own species. H. heidelbergensis has similarities to both H. erectus and the later species. The H. neanderthalensis, even if it may have been a transitional species between middle Homo and the line to which modern humans belong.
Homo ergaster probably first evolved in Africa around two million years ago. This species had a rounded cranium with a brain size of between 700 and 850 cu. cm. (49 to 52 cu. in.) a prominent brow ridge, small teeth, and many other features that it shared with the later H. erectus. Many paleoanthropologists consider H. ergaster a good candidate for an ancestor of modern humans because it had several modern skull features, including relatively thin cranial bones. Most H. ergaster fossils come from the time range of 1.8 million to 1.5 million years ago.
The most important fossil of this species yet found is a nearly complete skeleton of a young male from West Turkana, Kenya, which dates from about 1.55 million years ago. Scientists determined the sex of the skeleton from the shape of its pelvis. They also determined from patterns of tooth eruption and bone growth that the boy had died when he was between nine and 12 years old. The oldest humanlike fossils outside Africa have also been classified as H. ergaster, dated around 1.75 million year’s old. These finds, from the Dmanisi site in the southern Caucasus Mountains of Georgia, consist of several crania, jaws, and other fossilized bones. Some of these are strikingly like East African H. ergaster, but others are smaller or larger than H. ergaster, suggesting a high degree of variation within a single population
H. ergaster, H. rudolfensis, and H. habilis, in addition to possibly two robust Australopiths, all might have coexisted in Africa around 1.9 million years ago. This finding goes against a traditional paleoanthropological view that human evolution consisted of a single line that evolved progressively over time - an australopith species followed by early Homo, then middle Homo, and finally H. sapiens. It appears that periods of species diversity and extinction have been common during human evolution, and that modern H. sapiens has the rare distinction of being the only living human species today.
Although H. ergaster appears to have coexisted with several other human species, they probably did not interbreed. Mating rarely succeeds between two species with significant skeletal differences, such as H. ergaster and H. habilis. Many paleoanthropologists now believe that H. ergaster descended from an earlier population of Homo - perhaps one of the two known species of early Homo - and that the modern human line descended from the H. ergaster.
Paleoanthropologists now know that humans first evolved in Africa and lived only on that continent for a few million years. The earliest human species known to have spread in large numbers beyond the African continent was first discovered in Southeast Asia. In 1891 Dutch physician Eugne Dubois found the cranium of an early human on the Indonesian island of Java. He named this early human Pithecanthropus erectus, or ‘erect ape-man.’ Today paleoanthropologists call this species Homo erectus.
H. erectus appears to have evolved in Africa from earlier populations of H. ergaster, and then spread to Asia sometime between 1.8 million and 1.5 million years ago. The youngest known fossils of this species, from the Solo River in Java, may date from about 50,000 years ago (although that dating is controversial). So,
H. erectus was a very successful species, - both widespread, having lived in Africa and much of Asia, and long-lived, having survived for possibly more than 1.5 million years.
H. erectus had a low and rounded braincase that was elongated form front to back, a prominent brow ridge, and adult cranial capacity of 800 to 1,250 cu. cm. (50 to 80 cu. in.), an average twice that of the Australopiths. Its bones, including the cranium, were thicker than those of earlier species. Prominent muscle markings and thick, reinforced areas on the bones of H. erectus indicate that its body could withstand powerful movements and stresses. Although it had much smaller teeth than did the Australopiths, it had a heavy and strong jaw.
In the 1920's and 1930's German anatomist and physical anthropologist Franz Weidenreich excavated the most famous collections of H. erectus fossils from a cave at the site of Zhoukoudian (Chou - k’ou - tien), China, near Beijing (Peking). Scientists dubbed these fossil humans Sinanthropus pekinensis, or Peking Man, but others later reclassified them as H. erectus. The Zhoukoudian cave yielded the fragmentary remains of more than 30 individuals, ranging from about 500,000 to 250,000 years old. These fossils were lost near the outbreak of World War II, but Weidenreich had made excellent casts of his finds. Further studies at the cave site have yielded more H. erectus remains.
Other important fossil sites for this species in China include Lantian, Yuanmou, Yunxian, and Hexian. Researchers have also recovered many tools made by H. erectus in China at sites such as Nihewan and Bose, and other sites of similar age (at least one million to 250,000 years old).
Ever since the discovery of H. erectus, scientists have debated whether this species was a direct ancestor of later humans, including H. sapiens. The last populations of H. erectus - such as those from the Solo River in Java - may have lived as recently as 50,000 years ago, while did populations of H. sapiens. Modern humans could not have evolved from these late populations of the
H. erectus, a much more primitive type of human. However, earlier East Asian populations could have produced H. sapiens.
Many paleoanthropologists believe that early humans migrated into Europe by 800,000 years ago, and that these populations were not Homo erectus. Most scientists refer to these early migrants into Europe, - who predated both Neanderthals and H. sapiens in the region, as H. heidelbergensis. The species name comes from a 500,000-year-old jaw found near Heidelberg, Germany
Scientists have found few human fossils in Africa for the period between 1.2 million and 600,000 years ago, during which H. heidelbergensis or its ancestors first migrated into Europe. Populations of H. ergaster (or possibly H. erectus) appear to have lived until at least 800,000 years ago in Africa, and possibly until 500,000 years ago in northern Africa. When these populations disappeared, other massive-boned and larger-brained humans - possibly H. heidelbergensis - appear to have replaced them. Scientists have found fossils of these stockier humans at sites in Bodo, Ethiopia; Saldanha (also known as Elandsfontein), South Africa; Ndutu, Tanzania; and Kabwe, Zimbabwe.
Scientists have come up with at least three different interpretations of these African fossils. Some scientists place the fossils in the species H. heidelbergensis and think that this species led to both the Neanderthals (in Europe) and H. sapiens (in Africa). Others think that the European and African fossils belong to two distinct species, and that the African populations that, in this view, was not H. heidelbergensis but a separate species produced H. sapiens. Yet other scientists advocate a long-head view that
H. erectus and H. sapiens belong to a single evolving lineage, and that the African fossils belong in the category of archaic H. sapiens (archaic meaning not fully anatomically modern).
The fossil evidence does not clearly favour any of these three interpretations over another. Several fossils from Asia, Africa, and Europe have features that are intermediate between early
H. ergaster and H. sapiens. This kind of variation makes it hard to decide how to identify distinct species and to determine which group of fossils represents the most likely ancestor of later humans.
Scientists once thought that advances in stone tools could have enabled early humans such as Homo erectus to move into Asia and Europe, perhaps by helping them to obtain new kinds of food, such as the meat of large mammals. If African human populations had developed tools that allowed them to hunt large game effectively, they would have had a good source of food wherever they went. In this view, humans first migrated into Eurasia based on a unique cultural adaptation.
By 1.5 million years ago, early humans had begun to make new kinds of tools, which scientists call Acheulean. Common Acheulean tools included large hand axes and cleavers. While these new tools might have helped early humans to hunt, the first known Acheulean tools in Africa date from later than the earliest known human presence in Asia. Also, most East Asian sites more than 200,000 years old contains only simply shaped cobble and flake tools. In contrast, Acheulean tools were more finely crafted, larger, and more symmetrical. Thus, the earliest settlers of Eurasia did not have a true Acheulean technology, and advances in toolmaking alone cannot explain the spread out of Africa.
Another possibility is that the early spreads of humans to Eurasia were not unique, but part of a wider migration of meat - eating animals, such as lions and hyenas. The human migration out of Africa occurred during the early part of the Pleistocene Epoch, between 1.8 million and 780,000 years ago. Many African carnivores spread to Eurasia during the early Pleistocene, and humans could have moved along with them. In this view, H. erectus was one of many meat-eating species to expand into Eurasia from Africa, rather than a uniquely adapted species. Relying on meat as a primary food source might have allowed many meat - eating species, including humans, to move through many different environments without having to learn about unfamiliar and potentially poisonous plants quickly.
However, the migration of humans to eastern Asia may have occurred gradually and through lower latitudes and environments similar to those of Africa. If East African populations of H. erectus moved at only 1.6 km. (1 mi.) every 20 years, they could have reached Southeast Asia in 150,000 years. Over this amount of time, humans could have learned about and begun relying on edible plant foods. Thus, eating meat may not have played a crucial role in the first human migrations to new continents. Careful comparison of animal fossils, stone tools, and early human fossils from Africa, Asia, and Europe will help scientists better to determine what factors motivated and allowed humans to venture out of Africa for the first time.
The origin of our own species, Homo sapiens, is one of the most hotly debated topics in Paleoanthropology. This debate centres on whether or not modern humans have a direct relationship to
H. erectus or to the Neanderthals, and to a great extent is acknowledged of the more modern group of humans who evolved within the past 250,000 years. Paleoanthropologists commonly use the term anatomically modern Homo sapiens to distinguish people of today from these similar predecessors.
Traditionally, paleoanthropologists classified as Homo sapiens any fossil human younger than 500,000 years old with a braincase larger than that of H. erectus. Thus, many scientists who believe that modern humans descend from a single line dating back to H. erectus use the name archaic Homo sapiens to refer to a variety of fossil humans that predate anatomically modern H. sapiens. The designate with archaic denote a set of physical features typical of Neanderthals and other species of late Homo before modern Homo sapiens. These features include a combination of a robust skeleton, a large but low braincase (positioned somewhat behind, rather than over, the face), and a lower jaw lacking a prominent chin. In this sense, Neanderthals are sometimes classified as a subspecies of archaic H. sapiens and H. Sapiens neanderthalensis. Other scientists think that the variation in archaic fossils falls into clearly identifiable sets of traits, and that any type of human fossil exhibiting a unique set of traits should have a new species name. According to this view, the Neanderthals belong to their own species, H. neanderthalensis.
The Neanderthals lived in areas ranging from western Europe through central Asia from about 200,000 to about 28,000 years ago. The name Neanderthal (sometimes spelled Neanderthal) comes from fossils found in 1856 in the Feldhofer Cave of the Neander Valley in Germany (tal, - a modern form of that - means ‘valley’ in German). Scientists realized several years later that prior discoveries, at Engis, Belgium, in 1829 and at Forbes Quarry, Gibraltar, in 1848, - also represented Neanderthal. These two earlier discoveries were the first early human fossils ever found
In the past, scientists claimed that Neanderthal differed greatly from modern humans. However, the basis for this claim came from a faulty reconstruction of a Neanderthal skeleton that showed it with bent knees and a slouching gait. This reconstruction gave the common but mistaken impression that Neanderthals were dim-witted brutes who lived a crude lifestyle. On the contrary, Neanderthals, like the species that preceded them, walked fully upright without a slouch or bent knees. In addition, their cranial capacity was quite large at about 1,500 cu. cm. (about 90 cu. in.), larger on average than that of modern humans. (The difference probably relates to the greater muscle mass of Neanderthals as compared with modern humans, which usually correlates with a larger brain size.)
Compared with earlier humans, Neanderthals had a high degree of cultural sophistication. They appear to have acted symbolic rituals, such as the burial of their dead. Neanderthal fossils, - including some complete skeletons is quite common compared with those of earlier forms of Homo, in part because of the Neanderthal practice of intentional burial. Neanderthals also produced sophisticated types of stone tools known as Mousterian, which involved creating blanks (rough forms) from which several types of tools could be made. Along with many physical similarities, Neanderthals differed from modern humans in several ways. The typical Neanderthal skull had a low forehead, a large nasal area (suggesting a large nose), a forward-projecting nasal and cheek region, a prominent brow ridge with a bony arch over each eye, a nonprojecting chin, and obvious space behind the third molar (in front of the upward turn of the lower jaw).
Neanderthals also had a more heavily built and large-boned skeleton than do modern humans. Other Neanderthal skeletal features included a bowing of the limb bones in some individuals, broad scapulae (shoulder blades), hip joints turned outward, a long and thin pubic bone, short lower leg and arm bones relative to the upper bones, and large surfaces on the joints of the toes and limb bones. Together, these traits made a powerful, compact body of short stature males averaged 1.7 m. (5 ft. 5 in.) tall and 84 kg. (185 lb.), and females averaged 1.5 m. (5 ft.) tall and 80 kg. (176 lb.).
The short, stocky build of Neanderthals conserved heat and helped them withstand extremely cold conditions that prevailed in temperate regions beginning about 70,000 years ago. The last known Neanderthal fossils come from western Europe and date from approximately 36,000 years ago.
Just when Neanderthal populations grew in number in Europe and parts of Asia, other populations of nearly modern humans arose in Africa and Asia. Scientists also commonly refer to these fossils, which are distinct from but similar to those of Neanderthals, as archaic. Fossils from the Chinese sites of Dali, Maba, and Xujiayao display the long, low cranium and large face typical of archaic humans, yet they also have features similar to those of modern people in the region. At the cave site of Jebel Irhoud, Morocco, scientists have found fossils with the long skull typical of archaic humans but also the modern traits of a somewhat higher forehead and flatter midface. Fossils of humans from East African sites older than 100,000 years, such as Ngaloba in Tanzania and Eliye Springs in Kenya - also seem to show a mixture of archaic and modern traits.
The oldest known fossils that possess skeletal features typical of modern humans date from between 130,000 and 90,000 years ago. Several key features distinguish the skulls of modern humans from those of archaic species. These features include a much smaller brow ridge, if any; a globe-shaped braincase; and a flat or only projecting face of reduced size, located under the front of the braincase. Among all mammals, only humans have a face positioned directly beneath the frontal lobe (forward-most area) of the brain. As a result, modern humans tend to have a higher forehead than did Neanderthals and other archaic humans. The cranial capacity of modern humans ranges from about 1,000 to 2,000 cu. cm. (60 to 120 cu. in.), with the average being about 1,350 cu. cm. (80 cu. in.).
Scientists have found both fragmentary and nearly complete cranial fossils of early anatomically modern Homo sapiens from the sites of Singha, Sudan; Omo, Ethiopia; Klasies River Mouth, South Africa; and Skh~l Cave, Israel. Based on these fossils, many scientists conclude that modern H. sapiens had evolved in Africa by 130,000 years ago and started spreading to diverse parts of the world beginning on a route through the Near East sometime before 90,000 years ago.
Paleoanthropologists are engaged in an ongoing debate about where modern humans evolved and how they spread around the world. Differences in opinion rest on the question of whether the evolution of modern humans took place in a small region of Africa or over a broad area of Africa and Eurasia. By extension, opinions differ as to whether modern human populations from Africa displaced all existing populations of earlier humans, eventually resulting in their extinction.
Those who think modern humans originated only in Africa and then spread around the world support what is known as the out of Africa hypothesis. Those who think modern humans evolved over a large region of Eurasia and Africa support the so-called multiregional hypothesis.
The African origins of Humanity where Richard Leakey's work at Omo-Kibish gave scientists a fresh start in their study of Homo sapiens' origins. Indeed his finds gave them two beginnings. First, they led a few researchers in the 1970s to conclude that the Kibish man was a far more likely ancestor for the Cro-Magnons, a race of early Europeans who thrived about 25,000 years ago, than their immediate predecessors in Europe, the heavyset Neanderthals. Then in the 1980s, a new reconstruction and study of the Kibish man revealed an even more startling possibility - that he was a far better candidate as the forbear, not just for the Cro-Magnons but for every one of us alive today, not just Europeans but all the other peoples of the world, from the Eskimos of Greenland to the Twa people of Africa, and from Australian aborigines to Native Americans. In other words, the Kibish man acted as pathfinder for a new genesis for the human species.
In the past few years, many paleontologists, anthropologists, and geneticists have come to agree that this ancient resident of the riverbanks of Ethiopia and all his Kibish kin - both far and near - could indeed be among our ancestors. However, it has also become clear that the evolutionary pathway of these fledgling modern humans was not an easy one. At one stage, according to genetic data, our species became as endangered as the mountain gorilla is today, its population reduced to only about 10,000 adults. Restricted to one region of Africa, but tempered in the flames of near extinction, this population went on to make a remarkable comeback. It then spread across Africa until - nearly 100,000 years ago - it had colonized much of the continent's savannas and woodlands. We see the imprint of this spread in biological studies that have revealed that races within Africa are genetically the most disparate on the planet, indicating that modern humans have existed there in larger numbers for a longer time than anywhere else.
We can also observe intriguing clues about our African origins in other less obvious but equally exciting arenas. One example comes from Congo-Kinshasa. This huge tropical African country has never assumed much importance in the field of Paleoanthropology, the branch of anthropology concerned with the investigation of ancient humans. Unlike the countries to the east, Ethiopia, Kenya, and Tanzania, Congo-Kinshasa has provided few exciting fossil sites - until recently.
In the neglected western branch of the African Rift Valley, that giant geological slash that has played such a pivotal role in human evolution, the Semliki River runs northward between two large lakes, and its waters eventually from the source of the Nile. Along its banks, sediments are being exposed that were laid down 90,000 years ago, just as Homo sapiens was making its mark across Africa.
At the town of Katanda an archaeological treasure trove: thousands of artifacts, mostly stone tools, and a few bone implements that quite astonished the archaeologists, led by the husband-and-wife team of John Yellen, of the National Science Foundation, Washington, and Alison Brooks, of George Washington University. Among the wonders they have uncovered are sophisticated bone harpoons and knives. Previously it was thought that the Cro-Magnons were the first humans to develop such delicate carving skills - 000 years later. Yet this very much older grouped of Homo sapiens, living in the heartland of Africa, displayed the same extraordinary skills as craft’s workers. It was as if, said one observer, a prototype Pontiac car had been found in the attic of Leonardo da Vinci.
There were other surprises for researchers, however. Apart from the finely carved implements, they found fish bones, including some from two-metre-long catfish. It seems the Katanda people were efficiently and repeatedly catching catfish during their spawning season, indicating that systematic fishing is quite an ancient human skill and not some relatively recently acquired expertise, as many archaeologists had previously thought. In addition, the team found evidence that a Katanda site had at least two separate but similar clusters of stones and debris that looked like the residue of two distinct neighbouring groupings, signs of the possible impact of the nuclear family on society, a phenomenon that now defines the fabric of our lives.
Clearly, our African forbears were sophisticated people. Bands of them, armed with new proficiencies, like those men and women who had flourished on the banks of the Semliki, began an exodus from their African homeland. Slowly they trickled northward, and into the Levant, the region bordering the eastern Mediterranean. Then, by 80,000 years ago, small groups began spreading across the globe, via the Middle East, planting the seeds of modern humanity in Asia and later in Europe and Australia.
Today men and women conduct themselves in highly complex ways: some are uncovering the strange, indeterminate nature of matter, with its building blocks of quarks and leptons; some are probing the first few seconds of the origins of the universe 15 billion years ago; while others are trying to develop artificial brains capable of staggering feats of calculation. Yet the intellectual tools that allow us to investigate the deepest secrets of our world are the ones that were forged during our fight for survival, in a very different set of circumstances from those that prevail today. How on earth could an animal that struggled for survival like any other creature, whose time was absorbed in a constant search for meat, nuts, and tubers, and who had to maintain constant vigilance against predators, develop the mental hardwiring needed by a nuclear physicist or an astronomer? This is a vexing issue that takes us to the very heart of our African exodus, to the journey that brought us from precarious survival on a single continent to global control.
If we can ever hope to understand the special attributes that delineate a modern human being we have to attempt to solve such puzzles. How was the Kibish man different from his Neanderthal cousins in Europe, and what evolutionary pressures led the Katanda people to develop in such crucially different ways — ironically in the heart of a continent that has for far too long been stigmatized as backward?
Nonetheless, it remains bewildering, but French researchers announced at a press conference on May 22, 1996, the discovery of a new fossil hominid species in central Chad, estimated to have lived between 3 million and 3.5 million years ago. The fossilized remains of a lower jaw and seven teeth were found in 1995 near Koro Toro, in the desert about 2500 km (about 1500 mi) east of the Great Rift Valley in Africa, the site of many major hominid fossil finds. The leader of the French team that discovered the fossils at Bahr-el-Ghazal, Chad - paleontologist Michel Brunet of the University of Poitiers - named the species Australopithecus bahrelghazali (from the Arabic name of the nearby River of the Gazelles). The research team published its findings in the May 20 bulletin of the French Academy of Sciences. In a letter to the journal Nature published November 16, 1995, the researchers initially classified the fossil as an example of Australopithecus afarensis, the 3.4-million-year-old species that walked upright in eastern Africa. In the letter, Brunet said that more detailed comparisons with other fossils were necessary before he could determine that the jaw came from another species, and he noted that geographic separation can produce differences among animals of the same species. After the letter was published, Brunet travelled to museums to compare the jaw with other hominid bones. The fossil combines both primitive and modern hominid features. The jaw includes the right and left premolars, both canines, and the right lateral incisor. Brunet said the strong canine teeth and the shape of the incisor resemble human teeth more than ape teeth. The chin area is more vertical than the backward-sloping chin of A. afarensis, and it lacks the strong reinforcement for chewing power found among other early hominids. However, the premolars retain primitive characteristics, such as three roots, and modern humans have only one root. Scientists said they needed more fossil material before they can place the species on the evolutionary tree. Brunet cited the find as the first evidence of hominid occupation of areas outside the Great Rift Valley and South Africa, where anthropologists have concentrated their search for hominid fossils. Other experts noted that the eroding volcanic soils in the Great Rift Valley are simply better for preserving and exposing fossils than the soils in most other regions in Africa. Although many digs have occurred in the Great Rift Valley, most scientists believe that hominids existed throughout Africa.
Researchers have conducted many genetic studies and carefully assessed fossils to determine which of these hypotheses agrees more with scientific evidence. The results of this research do not entirely confirm or reject either one. Therefore, some scientists think a compromise between the two hypotheses is the best explanation. The debate between these views has implications for how scientists understand the concept of race in humans. The question raised is whether the physical differences among modern humans evolved deep in the past or relatively recently, according to the out of Africa hypothesis, also known as the replacement hypothesis, early populations of modern humans from Africa migrated to other regions and entirely replaced existing populations of archaic humans. The replaced populations would have included the Neanderthals and any surviving groups of Homo erectus. Supporters of this view note that many modern human skeletal traits evolved relatively recently, - within the past 200,000 years or so suggesting a single, common origin. In addition, the anatomical similarities shared by all modern human populations far outweigh those shared by premodern and modern humans within particular geographic regions. Furthermore, biological research indicated that most new species of organisms, including mammals, arose from small, geographically isolated populations.
According to the multiregional hypothesis, also known as the continuity hypothesis, the evolution of modern humans began when Homo erectus spread throughout much of Eurasia around one million years ago. Regional populations retained some unique anatomical features for hundreds of thousands of years, but they also mated with populations from neighbouring regions, exchanging heritable traits with each other. This exchange of heritable traits is known as gene flow.
Through gene flow, populations of H. erectus passed on a variety of increasingly modern characteristics, such as increases in brain size, across their geographic range. Gradually this would have resulted in the evolution of more modern looking humans throughout Africa and Eurasia. The physical differences among people today, then, would result from hundreds of thousands of years of regional evolution. This is the concept of continuity. For instance, modern East Asian populations have some skull features that scientists also see in H. erectus fossils from that region.
Some critics of the multiregional hypothesis claim that it wrongly advocates a scientific belief in race and could be used to encourage racism. Supporters of the theory point out, however, that their position does not imply that modern races evolved in isolation from each other, or that racial differences justify racism. Instead, the theory holds that gene flow linked different populations together. These links allowed progressively more modern features, no matter where they arose, to spread from region to region and eventually become universal among humans.
Scientists have weighed the out of Africa and multiregional hypotheses against both genetic and fossil evidence. The results do not unanimously support either one, but weigh more heavily in favour of the out of Africa hypothesis.
Geneticists have studied difference in the DNA (deoxyribonucleic acid) of different populations of humans. DNA is the molecule that contains our heritable genetic code. Differences in human DNA result from mutations in DNA structure. Mutations may result from exposure to external elements such as solar radiation or certain chemical compounds, while others occur naturally at random.
Geneticists have calculated rates at which mutations can be expected to occur over time. Dividing the total number of genetic differences between two populations by an expected rate of mutation provides an estimate of the time when the two shared a common ancestor. Many estimates of evolutionary ancestry rely on studies of the DNA in cell structures called mitochondria. This DNA is called mtDNA (mitochondrial DNA). Unlike DNA from the nucleus of a cell, which codes for most of the traits an organism inherits from both parents, MtDNA inheritance passes only from a mother to her offspring. MtDNA also accumulates mutations about ten times faster than does DNA in the cell nucleus (the location of most DNA). The structure of MtDNA changes so quickly that scientists can easily measure the differences between one human population and another. Two closely related populations should have only minor differences in their MtDNA. Conversely, two very distantly related populations should have large differences in their MtDNA
MtDNA research into modern human origins has produced two major findings. First, the entire amount of variation in MtDNA across human populations is small in comparison with that of other animal species. This means that all human MtDNA originated from a single ancestral lineage - specifically, a single female - recently and has been mutating ever since. Most estimates of the mutation rate of MtDNA suggest that this female ancestor lived about 200,000 years ago. In addition, the MtDNA of African populations varies more than that of peoples in other continents. This suggests that the MtDNA of African populations sustained of change for a longer time than in populations of any other region. That all living people inherited their MtDNA from one woman in Africa, who is sometimes called the Mitochondrial Eve. Some geneticists and anthropologists have concluded from this evidence that modern humans originated in a small population in Africa and spread from there.
MtDNA studies have weaknesses, however, including the following four. First, the estimated rate of MtDNA mutation varies from study to study, and some estimates put the date of origin closer to 850,000 years ago, the time of Homo erectus. Second, MtDNA makes up a small part of the total genetic material that humans inherit. The rest of our genetic material - about 400,000 times more than the MtDNA, - came from many individuals living at the time of the African Eve, conceivably from many different regions. Third, the time at which modern MtDNA began to diversify does not necessarily coincide with the origin of modern human biological traits and cultural abilities. Fourth, the smaller amount of modern MtDNA diversity but Africa could result from times when European and Asian populations declined in numbers, perhaps due to climate changes.
Despite these criticisms, many geneticists continue to favour the out of Africa hypothesis of modern human origins. Studies of nuclear DNA also suggest an African origin for a variety of genes. Furthermore, in a remarkable series of studies in the late 1990's, scientists recovered MtDNA from the first Neanderthal fossil found in Germany and two other Neanderthal fossils. In each case, the MtDNA does not closely match that of modern humans. This finding suggests that at least some Neanderthal populations had diverged from the line to modern humans by 500,000 to 600,000 years ago. This also suggests that Neanderthals represent a separate species from modern H. sapiens. In another study, however, MtDNA extracted from a 62,000-year-old Australian H. sapiens fossil was found to differ significantly from modern human MtDNA, suggesting a much wider range of MtDNA variation within H. sapiens than was previously believed. According to the Australian researchers, this finding lends support to the multiregional hypothesis because it shows that different populations of H. sapiens, possibly including Neanderthals, could have evolved independently in different parts of the world.
As with genetic research, fossil evidence also does not entirely support or refute either of the competing hypotheses of modern human origins. However, many scientists see the balance of evidence favouring an African origin of modern H. sapiens within the past 200,000 years. The oldest known modern-looking skulls come from Africa and date from perhaps 130,000 years ago. The next oldest comes from the Near East, where they date from about 90,000 years ago. Fossils of modern humans in Europe do not exist from before about 40,000 years ago. In addition, the first modern humans in Europe - often called Cro-Magnon people - had elongated lower leg bones, as did African populations adapted too warm, tropical climates. This suggests that populations from warmer regions replaced those in colder European regions, such as the Neanderthals.
Fossils also show that populations of modern humans lived when and in the same regions as did populations of Neanderthals and Homo erectus, but that each retained its distinctive physical features. The different groups overlapped in the Near East and Southeast Asia for between about 30,000 and 50,000 years. The maintenance of physical differences for this amount of time implies that archaically and modern humans could either not or generally did not interbreed. To some scientists, this also means that the Neanderthals belong to a separate species, H. neanderthalensis, and that migratory populations of modern humans entirely replaced archaic humans in both Europe and eastern Asia.
On the other hand, fossils of archaic and modern humans in some regions show continuity in certain physical characteristics. These similarities may indicate multiregional evolution. For example, both archaic and modern skulls of eastern Asia have flatter cheek and nasal areas than do skulls from other regions. By contrast, the same parts of the face project forward in the skulls of both archaic and modern humans of Europe. If these traits were influenced primarily by genetic inheritance rather than environmental factors, archaic humans may have produced modern humans in some regions or at least interbred with migrant modern-looking humans.
Each of the competing major hypotheses of modern human origins has its strengths and weaknesses. Genetic evidence appears to support the out of Africa hypothesis. In the western half of Eurasia and in Africa, this hypothesis also seems the better explanation, particularly as for the apparent replacement of Neanderthals by modern populations. Also, the multiregional hypothesis appears to explain some of the regional continuity found in East Asian populations.
Therefore, many paleoanthropologists advocate a theory of modern human origins that combine elements of the out of Africa and the multiregional hypotheses. Humans with modern features may have initiatively emerged in Africa or come together there as a result of gene flow with populations from other regions. These African populations may then have replaced archaic humans in certain regions, such as western Europe and the Near East. Still, elsewhere, - especially in East Asia- gene flow may have occurred among local populations of archaic and modern humans, resulting in distinct and enduring regional characteristics.
All three of these views, - the two competing positions and the compromiser acknowledge the strong biological unity of all people. In the multiregional hypothesis, this unity results from hundreds of thousands of years of continued gene flow among all human populations. According to the out of Africa hypothesis, on the other hand, similarities among all living human populations result from a recent common origin. The compromise position accepts both as reasonable and compatible explanations of modern human origins.
The story of human evolution is as much about the development of cultural behaviour as it is about changes in physical appearance. The term culture, in anthropology, traditionally refers to all human creations and activities governed by social customs and rules. It includes elements such as technology, language, and art. Human cultural behaviour depends on the social transfer of information from one generation to the next, which it depends on a sophisticated system of communication, such as language.
The term culture has often been used to distinguish the behaviour of humans from that of other animals. However, some nonhuman animals also appear to have forms of learned cultural behaviours. For instance, different groups of chimpanzees use different techniques to capture termites for food using sticks. Also, in some regions chimps use stones or pieces of wood for cracking open nuts. Chimps in other regions do not practice this behaviour, although their forests have similar nut trees and materials for making tools. These regional differences resemble traditions that people pass from generation to generation. Traditions are a fundamental aspect of culture, and paleoanthropologists assume that the earliest humans also had some types of traditions.
However, modern humans differ from other animals, and probably many early human species, in that they actively teach each other and can pass on and accumulate unusually large amounts of knowledge. People also have a uniquely long period of learning before adulthood, and the physical and mental capacity for language. Language of all forms spoken, signed, and written, - provides a medium for communicating vast amounts of information, much more than any other animal could probably transmit through gestures and vocalizations.
Scientists have traced the evolution of human cultural behaviour through the study of archaeological artifacts, such as tools, and related evidence, such as the charred remains of cooked food. Artifacts show that throughout much of human evolution, culture has developed slowly. During the Palaeolithic, or early Stone Age, basic techniques for making stone tools changed very little for periods of well more than a million years.
Human fossils also provide information about how culture has evolved and what effects it has had on human life. For example, over the past 30,000 years, the basic anatomy of humans has undergone only one prominent change: The bones of the average human skeleton have become much smaller and thinner. Innovations in the making and use of tools and in obtaining food, - results of cultural evolution may have led to more efficient and less physically taxing lifestyles, and thus caused changes in the skeleton.
Culture has played a prominent role in the evolution of Homo sapiens. Within the last 60,000 years, people have migrated to settle most unoccupied regions of the world, such as small island chains and the continents of Australia and the Americas. These migrations depended on developments in transportation, hunting and fishing tools, shelter, and clothing. Within the past 30,000 years, cultural evolution has sped up dramatically. This change shows up in the archaeological record as a rapid expansion of stone tool types and toolmaking techniques, and in works of art and indications of evolving religion, such as burials. By 10,000 years ago, people first began to harvest and cultivate grains and to domesticate animals - a fundamental change in the ecological relationship between human beings and other life on Earth. The development of agriculture gave people larger quantities and more stable supplies of food, which set the stage for the rise of the first civilizations. Today, culture and particularly technology dominates human life.
Paleoanthropologists and archaeologists have studied many topics in the evolution of human cultural behaviour. These have included the evolution of (1) social life; (2) subsistence (the acquisition and production of food); (3) the making and using of tools; (4) environmental adaptation; (5) symbolic thought and its expression through language, art, and religion; and (6) the development of agriculture and the rise of civilizations.
Most primate species, including the African apes, live in social groups of varying size and complexity. Within their groups, individuals often have multifaceted roles, based on age, sex, status, social skills, and personality. The discovery in 1975 at Hadar, Ethiopia, of a group of several Australopithecus afarensis individuals who died together 3.2 million years ago appears to confirm that early humans lived in social groups. Scientists have referred to this collection of fossils as The First Family.
One of the first physical changes in the evolution of humans from apes - a decrease in the size of male canine teeth - also, indicating a change in social relations. Male apes sometimes use their large canines to threaten (or sometimes fight with) other males of their species, usually over access to females, territory, or food. The evolution of small canines in Australopiths implies that males had either developed other methods of threatening each other or become more cooperative. In addition, both male and female Australopiths had small canines, indicating a reduction of sexual dimorphism from that in apes. Yet, although sexual dimorphism in canine size decreased in Australopiths, males were still much larger than females. Thus, male Australopiths might have competed aggressively with each other based on sheer size and strength, and the social life of humans may not have differed much from that of apes until later times.
Scientists believe that several of the most important changes from apelike to characteristically human social life occurred in species of the genus Homo, whose members show even less sexual dimorphism. These changes, which may have occurred at different times, included, (1) prolonged maturation of infants, including an extended period during which they required intensive care from their parents; (2) special bonds of sharing and exclusive mating between particular males and females, called pair-bonding; and (3) the focus of social activity at a home base, a safe refuge in a special location known to family or group members.
Humans, who have a large brain, has a prolonged period of infant development and childhood because the brain takes a long time too mature. Since the australopith brain was not much larger than that of a chimp, some scientists think that the earliest humans had a more apelike rate of growth, which is far more rapid than that of modern humans. This view is supported by studies of australopith fossils looking at tooth development - a good indicator of overall body development.
In addition, the human brain becomes very large as it develops, so a woman must give birth at an early stage of development in order for the infant’s head to fit through her birth canal. Thus, human babies require a long period of care to reach a stage of development at which they depend less on their parents. In contrast with a modern female, a female australopith could give birth to a baby at an advanced stage of development because its brain would not be too large to pass through the birth canal. The need to give birth early - and therefore to provide more infant care, - may have evolved around the time of the middle Homo’s species Homo’s ergaster. This species had a brain significantly larger than that of the Australopiths, but a narrow birth canal.
Pair-bonding, usually of a short duration, occurs in a variety of primate species. Some scientists speculate that prolonged bonds developed in humans along with increased sharing of food. Among primates, humans have a distinct type of food-sharing behaviour. People will delay eating food until they have returned with it to the location of other members of their social group. This type of food sharing may have arisen at the same time as the need for intensive infant care, probably by the time of H. ergaster. By devoting himself to a particular female and sharing food with her, a male could increase the chances of survival for his own offspring.
Humans have lived as foragers for millions of years. Foragers obtain food when and where it is available over a broad territory. Modern-day foragers (also known as hunter-gatherers) - such as the San people in the Kalahari Desert of southern Africa, - also set up central campsites, or home bases, and divide work duties between men and women. Women gather readily available plant and animal foods, while men take on the often less successful task of hunting. Female and male family members and relatives bring together their food to share at their home base. The modern form of the home base - that also serves as a haven for raising children and caring for the sick and elderly - may have first developed with middle Homo after about 1.7 million years ago. However, the first evidence of hearths and shelters common to all modern home bases, - comes from only after 500,000 years ago. Thus, a modern form of social life may not have developed until late in human evolution.
Human subsistence refers to the types of food humans eat, the technology used in and methods of obtaining or producing food, and the ways in which social groups or societies organize them for getting, making, and distributing food. For millions of years, humans probably fed on-the-go, much as other primates do. The lifestyle associated with this feeding strategy is generally organized around small, family-based social groups that take advantage of different food sources at different times of year.
The early human diet probably resembled that of closely related primate species. The great apes eat mostly plant foods. Many primates also eat easily obtained animal foods such as insects and bird eggs. Among the few primates that hunt, chimpanzees will prey on monkeys and even small gazelles. The first humans probably also had a diet based mostly on plant foods. In addition, they undoubtedly ate some animal foods and might have done some hunting. Human subsistence began to diverge from that of other primates with the production and use of the first stone tools. With this development, the meat and marrow (the inner, fat-rich tissue of bones) of large mammals became a part of the human diet. Thus, with the advent of stone tools, the diet of early humans became distinguished in an important way from that of apes.
Scientists have found broken and butchered fossil bones of antelopes, zebras, and other comparably sized animals at the oldest archaeological sites, which go of a date from some 2.5 million years ago. With the evolution of late Homo, humans began to hunt even the largest animals on Earth, including mastodons and mammoths, members of the elephant family. Agriculture and the domestication of animals arose only in the recent past, with H. sapiens.
Paleoanthropologists have debated whether early members of the modern human genus were aggressive hunters, peaceful plant gatherers, or opportunistic scavengers. Many scientists once thought that predation and the eating of meat had strong effects on early human evolution. This hunting hypothesis suggested that early humans in Africa survived particularly arid periods by aggressively hunting animals with primitive stone or bone tools. Supporters of this hypothesis thought that hunting and competition with carnivores powerfully influenced the evolution of human social organization and behaviour; toolmaking; anatomy, such as the unique structure of the human hand; and intelligence.
Beginning in the 1960's, studies of apes cast doubt on the hunting hypothesis. Researchers discovered that chimpanzees cooperate in hunts of at least small animals, such as monkeys. Hunting did not, therefore, entirely distinguish early humans from apes, and therefore hunting alone may not have determined the path of early human evolution. Some scientists instead argued in favour of the importance of food-sharing in early human life. According to a food-sharing hypothesis, cooperation and sharing within family groups - instead of aggressive hunting - strongly influenced the path of human evolution.
Scientists once thought that archaeological sites as much as two million years old provided evidence to support the food-sharing hypothesis. Some of the oldest archaeological sites were places where humans brought food and stone tools together. Scientists thought that these sites represented home bases, with many social features of modern hunter-gatherers campsites, including the sharing of food between pair-bonded males and females.
Critique of the food-sharing hypothesis resulted from more careful study of animal bones from the early archaeological sites. Microscopic analysis of these bones revealed the marks of human tools and carnivore teeth, indicating that both humans and potential predators, - such as, hyenas, cats, and jackals - were active at these sites. This evidence suggested that what scientists had thought were home bases where early humans shared food were in fact food-processing sites that humans abandoned to predators. Thus, evidence did not clearly support the idea of food-sharing among early humans.
The new research also suggested a different view of early human subsistence - that early humans scavenged meat and bone marrow from dead animals and did little hunting. According to this scavenging hypothesis, early humans opportunistically took parts of animal carcasses left by predators, and then used stone tools to remove marrow from the bones.
Observations that many animals, such as antelope, often die off in the dry season make the scavenging hypothesis quite plausible. Early toolmakers would have had plenty of opportunity to scavenge animal fat and meat during dry times of the year. However, other archaeological studies, - and a better appreciation of the importance of hunting among chimpanzees suggests that the scavenging hypothesis be too narrow. Many scientists now believe that early humans both scavenged and hunted. Evidence of carnivore tooth marks on bones cut by early human toolmakers suggests that the humans scavenged at least the larger of the animals they ate. They also ate a variety of plant foods. Some disagreement remains, however, about how much early humans relied on hunting, especially the hunting of smaller animals.
Scientists debate when humans first began hunting on a regular basis. For instance, elephant fossils were made-known to be found existent with tools made by middle Homo once led researchers to the idea that members of this species were hunters of big game. However, the simple association of animal bones and tools at the same site does not necessarily mean that early humans had killed the animals or eaten their meat. Animals may die in many ways, and natural forces can accidentally place fossils next to tools. Recent excavations at Olorgesailie, Kenya, show that H. erectus cut meat from elephant carcasses but do not reveal whether these humans were regular or specialized hunters
Humans who lived outside Africa, - especially in colder temperate climates almost needed to eat more meat than their African counterparts. Humans in temperate Eurasia would have had to learn about which plants they could safely eat, and the number of available plant foods would drop significantly during the winter. Still, although scientists have found very few fossils of edible or eaten plants at early human sites, early inhabitants of Europe and Asia probably did eat plant foods besides meat.
Sites that provide the clearest evidence of early hunting include Boxgrove, England, where about 500,000 years ago people trapped several large game animals between a watering hole and the side of a cliff and then slaughtered them. At Schningen, Germany, a site about 400,000 years old, scientists have found wooden spears with sharp ends that were well designed for throwing and probably used in hunting large animals.
Neanderthals and other archaic humans seem to have eaten whatever animals were available at a particular time and place. So, for example, in European Neanderthal sites, the number of bones of reindeer (a cold-weather animal) and red deer (a warm-weather animal) changed depending on what the climate had been like. Neanderthals probably also combined hunting and scavenging to obtain animal protein and fat.
For at least the past 100,000 years, various human groups have eaten foods from the ocean or coast, such as shellfish and some sea mammals and birds. Others began fishing in interior rivers and lakes. Between probably 90,000 and 80,000 years ago people in Katanda, in what is now the Democratic Republic of the Congo, caught large catfish using a set of barbed bone points, the oldest known specialized fishing implements. The oldest stone tips for arrows or spears date from about 50,000 to 40,000 years ago. These technological advances, probably first developed by early modern humans, indicate an expansion in the kinds of foods humans could obtain. Beginning 40,000 years ago humans began making even more significant advances in hunting dangerous animals and large herds, and in exploiting ocean resources. People cooperated in large hunting expeditions in which they killed many reindeer, bison, horses, and other animals of the expansive grasslands that existed at that time. In some regions, people became specialists in hunting certain kinds of animals. The familiarity these people had with the animals they hunted appears in sketches and paintings on cave walls, dating from as much as 32,000 years ago. Hunters also used the bones, ivory, and antlers of their prey to create art and beautiful tools. In some areas, such as the central plains of North America that once teemed with a now-extinct type of large bison (Bison occidentalis), hunting may have contributed to the extinction of entire species.
The making and use of tools alone probably did not distinguish early humans from their ape predecessors. Instead, humans made the important breakthrough of using one tool to make another. Specifically, they developed the technique of precisely hitting one stone against another, known as knapping. Stone toolmaking characterized the period that on give occasion to have to do with the Stone Age, which began at least 2.5 million years ago in Africa and lasted until the development of metal tools within the last 7,000 years (at different times in different parts of the world). Although early humans may have made stone tools before 2.5 million years ago, toolmakers may not have remained long enough in one spot to leave clusters of tools that an archaeologist would notice today.
The earliest simple form of stone toolmaking involved breaking and shaping an angular rock by hitting it with a palm-sized round rock known as a hammerstone. Scientists refer to tools made in this way as Oldowan, after Olduvai Gorge in Tanzania, a site from which many such tools have come. The Oldowan tradition lasted for about one million years. Oldowan tools include large stones with a chopping edge, and small, sharp flakes that could be used to scrape and slice. Sometimes Oldowan toolmakers used anvil stones (flat rocks found or placed on the ground) on which hard fruits or nuts could be broken open. Chimpanzees are known to do this today.
Humans have always adapted to their environments by adjusting their behaviour. For instance, early Australopiths moved both in the trees and on the ground, which probably helped them survive environmental fluctuations between wooded and more open habitats. Early Homo adapted by making stone tools and transporting their food over long distances, thereby increasing the variety and quantities of different foods they could eat. An expanded and flexible diet would have helped these toolmakers survive unexpected changes in their environment and food supply
When populations of H. erectus moved into the temperate regions of Eurasia, they faced new challenges to survival. During the colder seasons they had to either move away or seek shelter, such as in caves. Some of the earliest definitive evidence of cave dwellers dates from around 800,000 years ago at the site of Atapuerca in northern Spain. This site may have been home too early
H. heidelbergensis populations. H. erectus also used caves for shelter.
Eventually, early humans learned to control fire and to use it to create warmth, cook food, and protect themselves from other animals. The oldest known fire hearths date from between 450,000 and 300,000 years ago, at sites such as Bilzingsleben, Germany; Verteszöllös, Hungary; and Zhoukoudian (Chou - k’ou - tien), China. African sites as old as 1.6 million to 1.2 million years contain burned bones and reddened sediments, but many scientists find such evidence too ambiguous to prove that humans controlled fire. Early populations in Europe and Asia may also have worn animal hides for warmth during glacial periods. The oldest known bone needles, which indicate the development of sewing and tailored clothing, date from about 30,000 to 26,000 years ago.
Behaviour relates directly to the development of the human brain, and particularly the cerebral cortex, the part of the brain that allows abstract thought, beliefs, and expression through language. Humans communicate through the use of symbols - ways of referring to things, ideas, and feelings that communicate meaning from one individual to another but that need not have any direct connection to what they identify. For instance, a word, - one type of symbol - does not usually relate directly to the thing or idea it represents; it is abstract. English - speaking people use the word lion to describe a lion, not because a dangerous feline looks like the letter’s l-i-o-n, but because these letters together have a meaning created and understood by people.
People can also paint abstract pictures or play pieces of music that evoke emotions or ideas, even though emotions and ideas have no form or sound. In addition, people can conceive of and believe in supernatural beings and powers - abstract concepts that symbolize real-world events such as the creation of Earth and the universe, the weather, and the healing of the sick. Thus, symbolic thought lies at the heart of three hallmarks of modern human culture: language, art, and religion.
In language, people creatively join words together in an endless variety of sentences - each with a distinct meaning - according to a set of mental rules, or grammar. Language provides the ability to communicate complex concepts. It also allows people to exchange information about both past and future events, about objects that are not present, and about complex philosophical or technical concepts
Language gives people many adaptive advantages, including the ability to plan, to communicate the location of food or dangers to other members of a social group, and to tell stories that unify a group, such as mythologies and histories. However, words, sentences, and languages cannot be preserved like bones or tools, so the evolution of language is one of the most difficult topics to investigate through scientific study.
It appears that modern humans have an inborn instinct for language. Under normal conditions not developing language is almost impossible for a person, and people everywhere go through the same stages of increasing language skill at about the same ages. While people appear to have inborn genetic information for developing language, they learn specific languages based on the cultures from which they come and the experiences they have in life.
The ability of humans to have language depends on the complex structure of the modern brain, which has many interconnected, specific areas dedicated to the development and control of language. The complexity of the brain structures necessary for language suggests that it probably took a long time to evolve. While paleoanthropologists would like to know when these important parts of the brain evolved, endocasts (inside impressions) of early human skulls do not provide enough detail to show this.
Some scientists think that even the early Australopiths had some ability to understand and use symbols. Support for this view comes from studies with chimpanzees. A few chimps and other apes have been taught to use picture symbols or American Sign Language for simple communication. Nevertheless, it appears that language - as well as art and religious ritual - became vital aspects of human life only during the past 100,000 years, primarily within our own species.
Humans also express symbolic thought through many forms of art, including painting, sculpture, and music. The oldest known object of possible symbolic and artistic value dates from about 250,000 years ago and comes from the site of Berekhat Ram, Israel. Scientists have interpreted this object, a figure carved into a small piece of volcanic rock, as a representation of the outline of a female body. Only a few other possible art objects are known from between 200,000 and 50,000 years ago. These items, from western Europe and usually attributed to Neanderthals, include two simple pendants - a tooth and a bone with bored holes and several grooved or polished fragments of tooth and bone.
Sites dating from at least 400,000 years ago contain fragments of red and black pigment. Humans might have used these pigments to decorate bodies or perishable items, such as wooden tools or clothing of animal hides, but this evidence would not have survived to today. Solid evidence of the sophisticated use of pigments for symbolic purposes - such as in religious rituals, - comes only from after 40,000 years ago. From early in this period, researchers have found carefully made types of crayons used in painting and evidence that humans burned pigments to create a range of colours.
People began to create and use advanced types of symbolic objects between about 50,000 and 30,000 years ago. Much of this art appears to have been used in rituals - possibly ceremonies to ask spirit beings for a successful hunt. The archaeological record shows a tremendous blossoming of art between 30,000 and 15,000 years ago. During this period people adorned themselves with intricate jewellery of ivory, bone, and stone. They carved beautiful figurines representing animals and human forms. Many carvings, sculptures, and paintings depict stylized images of the female body. Some scientists think such female figurines represent fertility.
Early wall paintings made sophisticated use of texture and colour. The area of what is now. Southern France contains many famous sites of such paintings. These include the caves of Chauvet, which contain art more than 30,000 years old, and Lascaux, in which paintings date from as much as 18,000 years ago. In some cases, artists painted on walls that can be reached only with special effort, such as by crawling. The act of getting to these paintings gives them a sense of mystery and ritual, as it must have to the people who originally viewed them, and archaeologists refer to some of the most extraordinary painted chambers as sanctuaries. Yet no one knows for sure what meanings these early paintings and engravings had for the people who made them.
Graves from Europe and western Asia indicate that the Neanderthals were the first humans to bury their dead. Some sites contain very shallow graves, which group or family members may have dug simply to remove corpses from sight. In other cases it appears that groups may have observed rituals of grieving for the dead or communicating with spirits. Some researchers have claimed that grave goods, such as meaty animal bones or flowers, had been placed with buried bodies, suggesting that some Neanderthal groups might have believed in an afterlife. In a large proportion of Neanderthal burials, the corpse had its legs and arms drawn in close to its chest, which could indicate a ritual burial position.
Other researchers have challenged these interpretations, however. They suggest that perhaps the Neanderthals had practically rather than religious reasons for positioning dead bodies. For instance, a body manipulated into a fetal position would need only a small hole for burial, making the job of digging a grave easier. In addition, the animal bones and flower pollen near corpses could have been deposited by accident or without religious intention.
Many scientists once thought that fossilized bones of cave bears (a now-extinct species of large bear) found in Neanderthal caves indicated that these people had what has been referred to as a cave bear cult, in which they worshipped the bears as powerful spirits. However, after careful study researchers concluded that the cave bears probably died while hibernating and that Neanderthals did not collect their bones or worship them. Considering current evidence, the case for religion among Neanderthal remains controversial.
One of the most important developments in human cultural behaviours occurred when people began to domesticate (control the breeding of) plants and animals. Domestication and the advent of agriculture led to the development of dozens of staple crops (foods that forms the basis of an entire diet) in temperate and tropical regions around the world. Almost the entire population of the world today depends on just four of these major crops: wheat, rice, corn, and potatoes.
The growth of farming and animal herding initiated one of the most remarkable changes ever in the relationship between humans and the natural environment. The change first began just 10,000 years ago in the Near East and has accelerated very rapidly since then. It also occurred independently in other places, including areas of Mexico, China, and South America. Since the first domestication of plants and animals, many species over large areas of the planet have come under human control. The overall number of plant and animal species has decreased, while the populations of a few species needed to support large human populations have grown immensely. In areas dominated by people, interactions between plants and animals usually fall under the control of a single species - Homo sapiens.
By the time of the initial transition to plant and animal domestication, the cold, glacial landscapes of 18,000 years ago had long since given way to warmer and wetter environments. At first, people adapted to these changes by using a wider range of natural resources. Later they began to focus on a few of the most abundant and hardy types of plants and animals. The plant’s people began to use in large quantities included cereal grains, such as wheat in western Asia; wild varieties of rice in eastern Asia; and maize, of which corn is one variety, in what is now Mexico. Some of the animals people first began to herd included wild goats in western Asia, wild ancestors of chickens in eastern Asia, and llamas in South America.
By carefully collecting plants and controlling wild herd animals, people encouraged the development of species with characteristics favourable for growing, herding, and eating. This process of selecting certain species and controlling their breeding eventually created new species of plants, such as oats, barley, and potatoes; and animals, including cattle, sheep, and pigs. From these domesticated plant and animal species, people obtained important products, such as flour, milk, and wool.
By harvesting and herding domesticated species, people could store large quantities of plant foods, such as seeds and tubers, and have a ready supply of meat and milk. These readily available supplies gave people an abounding overindulgence - designate with a term food security. In contrast, the foraging lifestyle of earlier human populations never provided them with a significant store of food. With increased food supplies, agricultural peoples could settle into villages and have more children. The new reliance on agriculture and change to settled village life also had some negative effects. As the average diet became more dependent on large quantities of one or a few staple crops, people became more susceptible to diseases brought on by a lack of certain nutrients. A settled lifestyle also increased contact between people and between people and their refuse and waste matter, both of which acted to increase the incidence and transmission of disease.
People responded to the increasing population density - and a resulting overuse of farming and grazing lands - in several ways. Some people moved to settle entirely new regions. Others devised ways of producing food in larger quantities and more quickly. The simplest way was to expand onto new fields for planting and new pastures to support growing herds of livestock. Many populations also developed systems of irrigation and fertilization that allowed them to reuse crop-land and to produce greater amounts of food on existing fields.
The rise of civilizations - the large and complex types of societies in which most people still live today - developed along with surplus food production. People of high status eventually used food surpluses as a way to pay for labour and to create alliances among groups, often against other groups. In this way, large villages could grow into city-states (urban centres that governed them) and eventually empires covering vast territories. With surplus food production, many people could work exclusively in political, religious, or military positions, or in artistic and various skilled vocations. Command of food surpluses also enabled rulers to control labourers, such as in slavery. All civilizations developed based on such hierarchical divisions of status and vocation.
The earliest civilization arose more than 7,000 years ago in Sumer in what is now Iraq. Sumer grew powerful and prosperous by 5,000 years ago, when it centred on the city-state of Ur. The region containing Sumer, known as Mesopotamia, was the same area in which people had first domesticated animals and plants. Other centres of early civilizations include the Nile Valley of Northeast Africa, the Indus. Valley of South Asia, the Yellow River Valley of East Asia, the Oaxaca and Mexico valleys and the Yucatán region of Central America, and the Andean region of South America, China and Inca Empire
All early civilizations had some common features. Some of these included a bureaucratic political body, a military, a body of religious leadership, large urban centres, monumental buildings and other works of architecture, networks of trade, and food surpluses created through extensive systems of farming. Many early civilizations also had systems of writing, numbers and mathematics, and astronomy (with calendars); road systems; a formalized body of law; and facilities for education and the punishment of crimes. With the rise of civilizations, human evolution entered a phase vastly different from all before which came. Before this time, humans had lived in small, family-centred groups essentially exposed to and controlled by forces of nature. Several thousand years after the rise of the first civilizations, most people now live in societies of millions of unrelated people, all separated from the natural environment by houses, buildings, automobiles, and numerous other inventions and technologies. Culture will continue to evolve quickly and in unforeseen directions, and these changes will, in turn, influence the physical evolution of Homo sapiens and any other human species to come.
During the fist two billion years of evolution, bacteria were the sole inhabitants of the earth, and the emergence of a more complex form is associated with networking and symbiosis. During these two billion years, prokaryote, or organisms composed of cells with no nucleus (namely bacteria), transformed he earth’s surface and atmosphere. It was the interaction of these simple organisms that resulted in te complex processes of fermentation, photosynthesis, oxygen breathing, and the removal of nitrogen gas from the air. Such processes would not have evolved, however, if these organisms were atomized in the Darwinian sense or if the force of interaction between parts existed only outside the parts.
In the life of bacteria, bits of genetic material within organisms are routinely and rapidly transferred to other organisms. At any given time, an individual bacteria have the use of accessory gene, often from very different strains, which perform unprepared functions are not performed by its own DNA. Some of this genetic material can be incorporated into the DNA of the bacterium and some may be passed on to other bacteria. What this picture indicates, as Margulis and Sagan put it, is that ‘all the worlds’ bacteria have access to a single gene pool and hence to the adaptive mechanisms of the entire bacterial kingdom.’
Since the whole of this gene pool operates in some sense within the parts, the speed of recombination is much greater than that allowed by mutation alone, or by random changes inside parts that alter interaction between parts. The existence of the whole within parts explains why bacteria can accommodate change on a worldwide cale in a few years. If the only mechanism at work were mutation inside organisms, millions of years would require for bacteria to adapt to a global change in the conditions for survival. ‘By constantly and rapidly adapting to environmental conditions,’ wrote Margukis and Sagan, ‘the organisms of the microcosm support the entire biota, their global exchange network ultimately affecting every living plant and animal.’
The discovery of symbiotic alliance between organisms that become permanent is other aspect of the modern understanding of evolution that appears to challenge Darwin’s view of universal struggle between atomized individual organisms. For example, the mitochondria fond outside the nucleus of modern cells allows the cell to utilize oxygen and to exist in an oxygen-rich environment. Although mitochondria performs integral and essential functions in the life of the cell, they have their own genes composed of DNA, reproduced by simple division, and did so at time different from the rest of the cells.
The most reasonable explanation for this extraordinary alliance between mitochondria and the rest of the cell that oxygen-breathing bacteria in primeval seas combined with the organisms. These ancestors of modern mitochondria provided waste disposal and oxygen-derived energy in exchange for food and shelter and evolved via symbiosis more complex forms of oxygen-breathing life, since t whole of these organisms was lager than the sum of their symbiotic pats, this allowed for life functions that could not be performed by the mere collection of pasts. The existence of the whole within the parts coordinates metabolic functions and overall organization
Awaiting upon the unformidable arriving future, in which the future has framed its proposed new understanding of the relationship between mind and world within the larger content of the history of mathematical physics, the origin and extensions of the classical view of the functional preliminaries in association with scientific knowledge, and the various ways that physics has attempted to prevent previous challenges to the efficacy of classical epistemology. There is no basis in contemporary physics or biology for believing in the stark Cartesian division between mind and world that some have moderately described as ‘the disease of the Western mind.’ The dialectic orchestrations will serve as background for understanding a new relationship between parts and wholes in physics, with a similar view of that relationship that has emerged in the so-called ‘new-biology’ and in recent studies of the evolution of a scientific understanding to a more conceptualized representation of ideas, and includes its ally ‘content’.
Recent studies on the manner in which the brains of our ancestors evolved the capacity to acquire and use complex language systems also present us with a new view of the relationship between parts and wholes in the evolution of human consciousness. These studies suggest that cognitive narrations cannot fully explain the experience of consciousness about the physical substrates of consciousness, or that the whole that corresponds with any moment of conscious awareness is an emergent phenomenon that a stable and cohering cognizance cannot fully explain as to the sum of its constituent parts. This also suggests that the preadaptive change in the hominid brain that enhanced the capacity to use symbolic communication over a period of 2.5 million years cannot be fully explained as to the usual dynamics of Darwinian evolution
Recent studies on the manner in which the brains of our ancestors evolved the capacity to acquire and use complex language systems also present us with a new view of the relationship between parts and wholes in the evolution of human consciousness. These studies suggest that the experience of consciousness cannot be fully explained through the physical substrates of consciousness, or that the whole that corresponds with any moment of conscious awareness is an emergent phenomenon that cannot be fully explained as to the sum of its constituent parts. This also suggests that the preadaptive change in the hominid brain that enhanced the capacity to use symbolic communication over a period of 2.5 million years cannot be fully explained as for the usual dynamics of Darwinian evolution
Part and wholes in Darwinian theory cannot reveal the actual character of living organisms because that organism exists only in relation to the whole of biological life. What Darwin did not anticipate, however, is that the whole that is a living organism appears to exist in some sense within the parts, and that more complex life forms evolved in precesses in which synergy and cooperation between parts (organisms) result in new wholes (more complex of parts) withe emergent properties that do not exist in the collection of parts. More remarkable, this new understanding of the relationship between part and whole in biology seems very analogous to the disclosed by the discovery of non - locality in physics. We should stress, however, that this view of the relationship between parts and wholes in biologic reality is most orthodox and may occasion some controversy in the community of biological scientists.
Since Darwin’s understanding of the relations between part and whole was essentially classical and mechanistic, the new understanding of this relationship is occasioning some revising of his theory of evolution. Darwin made his theory public for the first time in a paper derived to the Linnean Society in 1858. The paper begins, ‘All nature is at war, one organism with another, or with anther external nature. In the Origins of Species, Darwin is more specific about the charter of this war. ‘There must be in every case a struggle for existence one individual either with another of the same species, or with the individual with another of the same species, or with the individuals of distinct species, or with physical condition of life.’ All these assumptions are apparent in Darwin’s definition of natural selection: If under chancing conditions of life organic brings present individual differences in almost every part of their structure, and that all construing metabolisms cannot dispute this: If there be, owing to their geometrical rate of an increase, a severe struggle for life to some age, season, or year, and this certainty can then, be considered the infinite complexity of the relating of all organic being to each other and to their conditions of life causing an infinite diversity in structure, constitution, habits, to be advantageous as those that it would be most extraordinary fact if no variations had ever occurred usefully to each being’ own welfare. Nevertheless, in the variations useful any organic being ever d occurred, absurdly individuals thus characterized will have the best chance of being preserved in the struggle for life, and from the strong principle of inheritances, that often have a tendency to produce offsprings similarly characterized. Thus the principle of preservation, of resembling the survival of the fittest - is called Natural Selection.
Based on the assumption that the study of variation in domestic animals and plants, ‘afforded the best and safest clue’ to understanding evolution, Darwin concluded that nature could by crossbreeding and selection of traits, provide new species. His explanation of the mechanism in nature that results in a new specie took the form of a syllogism: (1) the principle of geometric increases indicated that more individuals in each species will have produced than can survive, (2) the struggle for existence occurs as one organism competes with another, (3) in this struggle for existence, slight variations, if they prove advantageous will accumulate to produce new species, in analogy with the animal breeder’s artificial selection of traits Darwin termed the elimination of the disadvantaged and the promotion of the advantaged natural selection.
In Darwin’s view, the struggle for existence occurs ‘between’ an atomized individual organism and of the atomized individual organisms in the same species, ‘between’ and atomized individual organisms of ne species with that of a different species, or ‘between’ an atomized individual organism ad the physical conditions of life the whole as Darwin conceived it is the collection of all atomized individual organisms, or parts. The struggle for survival occurs ‘between’ or ‘outside’ the parts. Since Darwin’s viewing this struggle as the only limiting condition in which the accountable rate of an increase in organises, he assumed that rate will be geometrical when the force of a struggle between parts is weak and that the rate will decline with the force becomes stronger.
Natural selection occurred, said Darwin, when variations ‘applicatively form; as each being accountable for through his own welfare,’ or useful to the welfare of an atomized individual organism, provides a survival advantage and the organism produces ‘offspring similarly characterized.’ Since the force that makes this selection operates ‘outside’ the totality of parts. For example, the ‘infinite complexities of relations of all organic beings to each other and to their condition of liveliness’ refers to dealing relations between parts, and the ‘infinite diversity in structure, constitute habit’ refers to remaining traits within the atomized part. It seems clear in our view that the atomized individual organism in Darwin’s biological machine reassembles classical atoms and that the force that drives the interactions of the atomized parts, the ‘struggle for life’ resembles Newton’s force of universal gravity. Although Darwin parted company with classical determinism in the claim that changes, of mutations, within organisms occurred randomly, his view of the relationship between parts and wholes essentially mechanistic.
Darwinism belief in the theory of ‘evolution’ by natural selection took form in its original formality from the observation of Malthus, although belonging principally to the history of science, as these encountering beliefs are met straight on into a philosophically influenced Malthus’s Essay on Population (1798) in undermining the Enlightenment belief in unlimited possibilities of human progress and perfection. The Origin of Species was principally successful in marshalling the evidence for evolution, than providing a convincing mechanism for genetic change; Darwin himself remained open to the search for additional in its mechanisms, while also remaining convinced that naturae section was at the heart of it. It was only with the later discovery of him ‘gene’ as the unit of inheritance hast the synthesis known as ‘neo - Darwinism’ became the orthodox theory of evolution in life sciences.
Human Evolution, is pressively the process through which a lengthy period of change is admissively given by people who have originated from apelike ancestors. Scientific evidence shows that the physical and behavioural traits shared by all people evolved over a period of at least six million years.
One of the earliest defining human traits, Bipedalism - walking on two legs as the primary form of locomotion - undergoes an evolution of more than four million years ago. Other important human characteristics - such as a large and complex brain, the ability to make and use tools, and the capacity for language - developed more recently. Many advanced traits, - including complex symbolic expression, such as art, and elaborate cultural diversity emerged mainly during the past 100,000 years.
Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Humans and the so-called great apes (large apes) of Africa - chimpanzees (including bonobos, or so-called pygmy chimpanzees) and gorillas, - share a common ancestor that lived sometime between eight million and six million years ago. The earliest humans evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between six million and two million years ago come entirely from Africa.
Early humans first migrated out of Africa into Asia probably between two million and 1.7 million years ago. They entered Europe somewhat later, generally within the past one million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years, and to the Americas within the past 35,000 years. The beginnings of agriculture and the rise of the first civilizations occurred within the past 10,000 years.
The scientific study of human evolution is called Paleoanthropology. Paleoanthropology is a sub-field of anthropology, the study of human culture, society, and biology. Paleoanthropologists search for the roots of human physical traits and behaviour. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, Paleoanthropology is an exciting scientific field because it illuminates the origins of the defining traits of the human species, as well as the fundamental connections between humans and other living organisms on Earth. Scientists have abundant evidence of human evolution from fossils, artifacts, and genetic studies. However, some people find the concept of human evolution troubling because it can seem to conflict with religious and other traditional beliefs about how people, other living things, and the world came to be. Yet many people have come to reconcile such beliefs with the scientific evidence.
All species of organisms originate through the process of biological evolution. In this process, new species arise from a series of natural changes. In animals that reproduce sexually, including humans, the term species refers to a group whose adult members regularly interbreed, resulting in fertile offspring, - that is, offspring themselves capable of reproducing. Scientists classify each species with a unique, and two-part scientific name. In this system, modern humans are classified as Homo sapiens.
The mechanism for evolutionary change resides in genes - the basic units of heredity. Genes affect how the body and behaviour of an organism develop during its life. The information contained in genes can change - a process known as mutation. The way particular genes are expressed - how they affect the body or behaviour of an organism - can also change. Over time, genetic change can alter a species’s overall way of life, such as what it eats, how it grows, and where it can live.
Genetic changes can improve the ability of organisms to survive, reproduce, and, in animals, raise offspring. This process is called adaptation. Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population - a group of organisms of the same species that share a particular local habitat. Many factors can favour new adaptations, but changes in the environment often play a role. Ancestral human species adapted to new environments as their genes changed, altering their anatomy (physical body structure), physiology (bodily functions, such as digestion), and behaviour. Over long periods, evolution dramatically transformed humans and their ways of life.
Geneticists estimate that the human line began to diverge from that of the African apes between eight million and five million years ago (paleontologists have dated the earliest human fossils, too, at least, six million years ago). This figure comes from comparing differences in the genetic makeup of humans and apes, and then calculating how long it probably took for those differences to develop. Using similar techniques and comparing the genetic variations among human populations around the world, scientists have calculated that all people may share common genetic ancestors that lived sometime between 290,000 and 130,000 years ago.
Humans belong to the scientific order named Primates, a group of more than 230 species of mammals that also includes lemurs, lorises, tarsiers, monkeys, and apes. Modern humans, early humans, and other species of primates all have many similarities as well as some important differences. Knowledge of these similarities and differences helps scientists to understand the roots of many human traits, as well as the significance of each step in human evolution.
All primates, including humans, share at least part of a set of common characteristics that distinguish them from other mammals. Many of these characteristics evolved as adaptations for life in the trees, the environment in which earlier primates evolved. These include more reliance on sight than smell; overlapping fields of vision, allowing stereoscopic (three-dimensional) sight; limbs and hands adapted for clinging on, leaping from, and swinging on tree trunks and branches; the ability to grasp and manipulate small objects (using fingers with nails instead of claws); large brains in relation to body size; and complex social lives.
The scientific classification of primates reflects evolutionary relationships between individual species and groups of species. Strepsirhine (meaning ‘turned-nosed’) primates - of which the living representatives include lemurs, lorises, and other groups of species all commonly known as prosimians - evolved earliest and are the most primitive forms of primates. The earliest monkeys and apes evolved from ancestral haplorhine (meaning ‘simple-nosed’) primates, of which the most primitive living representative is the tarsier. Humans evolved from ape ancestors.
Tarsiers have traditionally been grouped with prosimians, but many scientists now recognize that tarsiers, monkeys, and apes share some distinct traits, and group the three together. Monkeys, apes, and humans - who share many traits not found in other primates - together make up the suborder Anthropoidea. Apes and humans together make up the superfamily Hominoidea, a grouping that emphasizes the close relationship among the species of these two groups.
Strepsirhines are the most primitive types of living primates. The last common ancestors of Strepsirhines and other mammals - creatures similar to tree shrews and classified as Plesiadapiformes - evolved at least 65 million years ago. The earliest primates evolved by about 55 million years ago, and fossil species similar to lemurs evolved during the Eocene Epoch (about 55 million to 38 million years ago). Strepsirhines share all of the basic characteristics of primates, although their brains are not particularly large or complex and they have a more elaborate and sensitive olfactory system (sense of smell) than do other primates are the only living representatives of a primitive group of primates that ultimately led to monkeys, apes, and humans. Fossil species called omomyids, with some traits similar to those of tarsiers, evolved near the beginning of the Eocene, followed by early tarsier-like primates. While the omomyids and tarsiers are separate evolutionary branches (and there are no living omomyids), they both share features having to do with a reduction in the olfactory system, a trait shared by all haplorhine primates, including humans.
The anthropoid primates are divided into New World (South America, Central America, and the Caribbean Islands) and Old World (Africa and Asia) groups. New World monkeys - such as marmosets, capuchins, and spider monkeys - belong to the infra-order of platyrrhine (broad-nosed) anthropoids. Old World monkeys and apes belong to the infra-order of catarrhine (downward-nosed) anthropoids. Since humans and apes together make up the hominoids, humans are also catarrhine anthropoids.
The first catarrhine primates evolved between 50 million and 33 million years ago. Most primate fossils from this period have been found in a region of northern Egypt known as Al fay y~? m (or the Fayum). A primate group known as Propliopithecus, one lineage of which is sometimes called Aegyptopithecus, had primitive catarrhine features -that is, it had many of the basic features that Old World monkeys, apes, and humans share today. Scientists believe, therefore, that Propliopithecus resembles the common ancestor of all later Old World monkeys and apes. Thus, Propliopithecus may also be considered an ancestor or a close relative of an ancestor of humans evolved during the Miocene Epoch (24 million to 5 million years ago). Among the oldest known hominoids is a group of primates known by its genus name, Proconsul. Species of Proconsul had features that suggest a close link to the common ancestor of apes and humans - for example, the lack of a tail. The species Proconsul heseloni lived in the trees of dense forests in eastern Africa about 20 million years ago. An agile climber, it had the flexible backbone and narrow chest characteristic of monkeys, but also a wide range of movement in the hip and thumb, traits characteristic of apes and humans.
Large ape species had originated in Africa by 23 million or 22 million years ago. By 15 million years ago, some of these species had migrated to Asia and Europe over a land bridge formed between the Africa-Arabian and Eurasian continents, which had previously been separated.
Early in their evolution, the large apes underwent several radiations - periods when new and diverse species branched off from common ancestors. Following Proconsul, the ape genus Afropithecus evolved about 18 million years ago in Arabia and Africa and diversified into several species. Soon afterward, three other ape genera evolved - Griphopithecus of western Asia about 16.5 million years ago, the earliest ape to have spread from Africa; Kenyapithecus of Africa about 15 million years ago; and Dryopithecus of Europe about 12 million years ago. Scientists have not yet determined which of these groups of apes may have given rise to the common ancestor of modern African apes and humans.
Scientists do not all agree about the appropriate classification of hominoids. They group the living hominoids into either two or three families: Hylobatidae, Hominidae, and sometimes Pongidae. Hylobatidae consists of the small or so-called lesser apes of Southeast Asia, commonly known as gibbons and siamangs. The Hominidae (hominids) includes humans and, according to some scientists, the great apes. For those who include only humans among the Hominidae, all of the great apes, including the orangutans of Southeast Asia, belong to the family Pongidae.
In the past only humans were considered to belong to the family Hominidae, and the term hominid referred only to species of humans. Today, however, genetic studies support placing all of the great apes and humans together in this family and the placing of African apes - chimpanzees and gorillas - together with humans at an even lower level, or subfamily.
According to this reasoning, the evolutionary branch of Asian apes leading to orangutans, which separated from the other hominid branches by about 13 million years ago, belongs to the subfamily Ponginae. The ancestral and living representatives of the African ape and human branches together belong to the subfamily Homininae (sometimes called hominines). Lastly, the line of early and modern humans belongs to the tribe (classificatory level above genus) Hominini, or hominins.
This order of classification corresponds with the genetic relationships between ape and human species. It groups humans and the African apes together at the same level in which scientists group together, for example, all types of foxes, all buffalo, or all flying squirrels. Within each of these groups, the species are very closely related. However, in the classification of apes and humans the similarities among the name’s hominoid, hominid, hominine, and hominin can be confusing. In this article the term early human refers to all species of the human family tree since the divergence from a common ancestor with the African apes. Popular writing often still uses the term hominid to mean the same thing.
About 98.5 percent of the genes in people and chimpanzees are identical, making chimps the closest living biological relatives of humans. This does not mean that humans evolved from chimpanzees, but it does indicate that both species evolved from a common ape ancestor. Orangutans, the great apes of Southeast Asia, differ much more from humans genetically, indicating a more distant evolutionary relationship.
Modern humans have a number of physical characteristics reflective of an ape ancestry. For instance, people have shoulders with a wide range of movement and fingers capable of strong grasping. In apes, these characteristics are highly developed as adaptations for brachiation - swinging from branch to branch in trees. Although humans do not brachiate, the general anatomy from that earlier adaptation remains. Both people and apes also have larger brains and greater cognitive abilities than do most other mammals.
Human social life, too, shares similarities with that of African apes and other primates - such as baboons and rhesus monkeys - that live in large and complex social groups. Group behaviour among chimpanzees, in particular, strongly resembles that of humans. For instance, chimps form long-lasting attachments with each other; participate in social bonding activities, such as grooming, feeding, and hunting; and form strategic coalitions with each other in order to increase their status and power. Early humans also probably had this kind of elaborate social life.
However, modern humans fundamentally differ from apes in many significant ways. For example, as intelligent as apes are, people’s brains are much larger and more complex, and people have a unique intellectual capacity and elaborate forms of culture and communication. In addition, only people habitually walk upright, can precisely manipulate very small objects, and have a throat structure that makes speech possible.
By around six million years ago in Africa, an apelike species had evolved with two important traits that distinguished it from apes: (1) small canine, or eye, teeth (teeth next to the four incisors, or front teeth) and (2) Bipedalism, that is walking on two legs as the primary form of locomotion. Scientists refer to these earliest human species as australopithecines, or Australopiths for short. The earliest australopith species known today belong to three genera: Sahelanthropus, Orrorin, and Ardipithecus. Other species belong to the genus Australopithecus and, by some classifications, Paranthropus. The name australopithecine translates literally as ‘southern ape,’ in reference to South Africa, where the first known australopith fossils were found.
The Great Rift Valley, a region in eastern Africa in which past movements in Earth’s crust have exposed ancient deposits of fossils, has become famous for its australopith finds. Countries in which scientists have found australopith fossils include Ethiopia, Tanzania, Kenya, South Africa, and Chad. Thus, Australopiths ranged widely over the African continent.
Fossils from several different early australopith species that lived between four million and two million years ago clearly show a variety of adaptations that marks the transition from ape too human. The very early period of this transition, before four million years ago, remains poorly documented in the fossil record, but those fossils that do exist show the most primitive combinations of ape and human features.
Fossils reveal much about the physical build and activities of early Australopiths, but not everything about outward physical features such as the colour and texture of skin and hair, or about certain behaviours, such as methods of obtaining food or patterns of social interaction. For these reasons, scientists study the living great apes - particularly the African apes - better to understand how early Australopiths might have looked and behaved, and how the transition from ape too human might have occurred. For example, Australopiths probably resembled the great apes in characteristics such as the shape of the face and the amount of hair on the body. Australopiths also had brains roughly equal in size to those of the great apes, so they probably had apelike mental abilities. Their social life probably resembled that of chimpanzees.
Most of the distinctly human physical qualities in Australopiths related to their bipedal stance. Before Australopiths, no mammal had ever evolved an anatomy for habitual upright walking. Australopiths also had small canine teeth, as compared with long canines found in almost all other catarrhine primates.
Other characteristics of Australopiths reflected their ape ancestry. They had a low cranium behind a projecting face, and a brain size of 390 to 550 cu. cm. (24 to 34 cu. in.)—in the range of an ape’s brain. The body weight of Australopiths, as estimated from their bones, ranged from 27 to 49 kg. (60 to 108 lb.), and they stood 1.1 to 1.5 m. (3.5 to 5 ft.) tall. Their weight and height compare closely to those of chimpanzees (chimp height measured standing). Some australopith species had a large degree of sexual dimorphism - males were much larger than females - a trait also found in gorillas, orangutans, and another primates.
Australopiths also had curved fingers and long thumbs with a wide range of movement. In comparison, the fingers of apes are longer, more powerful, and more curved, making them extremely well adapted for hanging and swinging from branches. Apes also have very short thumbs, which limits their ability to manipulate small objects. Paleoanthropologists speculate as to whether the long and dexterous thumbs of Australopiths allowed them to use tools more efficiently than do apes.
The anatomy of Australopiths shows a number of adaptations for Bipedalism, in both the upper and lower body. Adaptations in the lower body included the following: The australopith ilium, or pelvic bone, which rises above the hip joint, was much shorter and broader than it is in apes. This shape enabled the hip muscles to steady the body during each step. The australopith pelvis also had a bowl-like shape, which supported the internal organs in an upright stance. The upper legs angled inward from the hip joints, which positioned the knees better to support the body during upright walking. The legs of apes, on the other hand, are positioned almost straight down from the hip, so that when an ape walks upright for a short distance, its body sways from side to side. Australopiths also had short and fewer flexible toes than do apes. The toes worked as rigid levers for pushing off the ground during each bipedal step.
Other adaptations occurred above the pelvis. The australopith spine had a S-shaped curve, which shortened the overall length of the torso and gave it rigidity and balance when standing. By contrast, apes have a relatively straight spine. The australopith skull also had an important adaptation related to Bipedalism. The opening at the bottom of the skull through which the spinal cord attaches to the brain, called the foramen magnum, was positioned more forward than it is in apes. This position set the head in balance over the upright spine.
Australopiths clearly walked upright on the ground, but paleoanthropologists debate whether the earliest humans also spent a significant amount of time in the trees. Certain physical features indicate that they spent at least some of their time climbing in trees. Such features included their curved and elongated fingers and elongated arms. However, their fingers, unlike those of apes, may not have been long enough to allow them to brachiate through the treetops. Study of fossil wrist bones suggests that early Australopiths had the ability to lock their wrists, preventing backward bending at the wrist when the body weight was placed on the knuckles of the hand. This could mean that the earliest bipeds had an ancestor that walked on its knuckles, as African apes do
Compared with apes, humans have very small canine teeth. Apes - particularly males - have thick, projecting, sharp canines that they use for displays of aggression and as weapons to defend themselves. The oldest known bipeds, who lived at least six million years ago, still had large canines by human standards, though not as large as in apes. By four million years ago Australopiths had developed the human characteristic of having smaller, flatter canines. Canine reduction might have related to an increase in social cooperation between humans and an accompanying decrease in the need for males to make aggressive displays.
The Australopiths can be divided into an early group of species, known as gracile Australopiths, which arose before three million years ago; and a later group, known as robust Australopiths, which evolved after three million years ago. The gracile Australopiths - of which several species evolved between 4.5 million and three million years ago - generally had smaller teeth and jaws. The later-evolving robusts had larger faces with large jaws and molars (cheek teeth). These traits indicate powerful and prolonged chewing of food, and analyses of wear on the chewing surface of robust australopith molar teeth support this idea. Some fossils of early Australopiths have features resembling those of the later species, suggesting that the robusts evolved from one or more gracile ancestors.
Paleoanthropologists recognize at least eight species of early Australopiths. These include the three earliest established species, which belong to the genera Sahelanthropus, Orrorin, and Ardipithecus, a species of the genus Kenyanthropus, and four species of the genus Australopithecus.
The oldest known australopith species is Sahelanthropus tchadensis. Fossils of this species were first discovered in 2001 in northern Chad, Central Africa, by a research team led by French paleontologist Michel Brunet. The researchers estimated the fossils to be between seven million and six million years old. One of the fossils is a cracked yet nearly complete cranium that shows a combination of apelike and humanlike features. Apelike features include small brain size, an elongated brain case, and areas of bone where strong neck muscles would have attached. Humanlike features made up of small, flat canine teeth, a short middle part of the face, and a massive brow ridge (a bony, protruding ridge above the eyes) similar to that of later human fossils. The opening where the spinal cord attaches to the brain is tucked under the brain case, which suggests that the head was balanced on an upright body. It is not certain that Sahelanthropus walked bipedally, however, because bones from the rest of its skeleton have yet to be discovered. Nonetheless, its age and humanlike characteristics suggest that the human and African ape lineages had divided from one another by at least six million years ago.
In addition to reigniting debate about human origins, the discovery of Sahelanthropus in Chad significantly expanded the known geographic range of the earliest humans. The Great Rift Valley and South Africa, from which almost all other discoveries of early human fossils came, are apparently not the only regions of the continent that preserve the oldest clues of human evolution.
Orrorin tugenensis lived about six million years ago. This species was discovered in 2000 by a research team led by French paleontologist Brigitte Senut and French geologist Martin Pickford in the Tugen Hills region of central Kenya. The researchers found more than a dozen early human fossils dating between 6.2 million and six million years old. Among the finds were two thighbones that possess a groove indicative of an upright stance and bipedal walking. Although the finds are still being studied, the researchers consider these thighbones to be the oldest evidence of habitual two-legged walking. Fossilized bones from other parts of the skeleton show apelike features, including long, curved finger bones useful for strong grasping and movement through trees, and apelike canine and premolar teeth. Because of this distinctive combination of ape and human traits, the researchers gave a new genus and species name to these fossils, Orrorin tugenensis, which in the local language means ‘original man in the Tugen region.’ The age of these fossils suggests that the divergence of humans from our common ancestor with chimpanzees occurred before six million years ago.
In 1994 an Ethiopian member of a research team led by American paleoanthropologist Tim White discovered human fossils estimated to be about 4.4 million year’s old. White and his colleagues gave their discovery the name Ardipithecus ramidus. Ramid means ‘root’ in the Afar language of Ethiopia and refers to the closeness of this new species to the roots of humanity. At the time of this discovery, the genus Australopithecus was scientifically well established. White devised the genus name Ardipithecus to distinguish this new species from other Australopiths because its fossils had a very ancient combination of apelike and humanlike traits. More recent finds indicate that this species may have lived as early as 5.8 million to 5.2 million years ago.
The teeth of Ardipithecus ramidus had a thin outer layer of enamel - a trait also seen in the African apes but not in other australopith species or older fossil apes. This trait suggests a close relationship with an ancestor of the African apes. In addition, the skeleton shows strong similarities to that of a chimpanzee but has slightly reduced canine teeth and adaptations for Bipedalism.
In 1965 a research team from Harvard University discovered a single arm bone of an early human at the site of Kanapoi in northern Kenya. The researchers estimated this bone to be four million years old, but could not identify the species to which it belonged or return at the time to look for related fossils. It was not until 1994 that a research team, led by British-born Kenyan paleoanthropologist Meave Leakey, found numerous teeth and fragments of bone at the site that could be linked to the previously discovered fossil. Leakey and her colleagues determined that the fossils were those of a species very primitives from those of the australopith, which was given the name Australopithecus anamensis. Researchers have since found other A. anamensis fossils at nearby sites, dating between about 4.2 million and 3.9 million years old. The skull of this species appears apelike, while its enlarged tibia (lower leg bone) indicates that it supported its full body weight on one leg at a time, as in regular bipedal walking
Australopithecus anamensis was quite similar to another, much better - known species, A. afarensis, a gracile australopith that thrived in eastern Africa between about 3.9 million and three million years ago. The most celebrated fossil of this species, known as Lucy, is a partial skeleton of a female discovered by American paleoanthropologist Donald Johanson in 1974 at Hadar, Ethiopia. Lucy lived 3.2 million years ago. Scientists have identified several hundred fossils of A. afarensis from Hadar, including a collection representing at least 13 individuals of both sexes and various ages, all from a single site.
Researchers working in northern Tanzania have also found fossilized bones of A. afarensis at Laetoli. This site, dated at 3.6 million years old, is best known for its spectacular trails of bipedal human footprints. Preserved in hardened volcanic ash, these footprints were discovered in 1978 by a research team led by British paleoanthropologist Mary Leakey. They provide irrefutable evidence that Australopiths regularly walked bipedally.
Paleoanthropologists have debated interpretations of the characteristics of A. afarensis and its place in the human family tree. One controversy centres on the Laetoli footprints, which some scientists believe show that the foot anatomy and gait of A. afarensis did not exactly match those of modern humans. This observation may suggest that early Australopiths did not live primarily on the ground or at least spent a significant amount of time in the trees. The skeleton of Lucy also suggests that A. afarensis had longer, more powerful arms than most later human species, suggesting that this species was adept at climbing trees.
Another controversy relates to the scientific classification of the A. afarensis fossils. Compared with Lucy, who stood only
1.1 m. (3.5 ft.) tall, other fossils identified as A. afarensis from Hadar and Laetoli came from individuals who stood up to 1.5 m.
(5 ft.) tall. This great difference in size leads some scientists to suggest that the entire set of fossils now classified as A. afarensis represents two species. Most scientists, however, believe the fossils represent one highly dimorphic species - that is, a species that has two distinct forms (in this case, two sizes). Supporters of this view note that both large (presumably male) and small (presumably female) adults occur together in one site at Hadar.
A third controversy arises from the claim that A. afarensis was the common ancestor of both later Australopiths and the modern human genus, Homo. While this idea remains a strong possibility, the similarity between this and another australopith species - one from southern Africa, named Australopithecus africanus - makes it difficult to decide which of the two species gave rise to the genus Homo.
Australopithecus africanus thrived in the Transvaal region of what is now South Africa between about 3.3 million and 2.5 million years ago. Australian-born anatomist Raymond Dart discovered this species - the first known australopith, - in 1924 at Taung, South Africa. The specimen that of a young child, came to be known as the Taung Child. For decades after this discovery, almost no one in the scientific community believed Dart’s claim that the skull came from an ancestral human. In the late 1930's teams led by Scottish-born South African paleontologist Robert Broom unearthed many more
A. africanus skulls and other bones from the Transvaal site of Sterkfontein.
A. africanus generally had a more globular braincase and less primitive-looking face and teeth than did A. afarensis. Thus, some scientists consider the southern species of early australopith to be a likely ancestor of the genus Homo. According to other scientists, however, certain heavily built facial and cranial features of
A. africanus from Sterkfontein identify it as an ancestor of the robust Australopiths that lived later in the same region. In 1998 a research team led by South African paleoanthropologist Ronald Clarke discovered an almost complete early australopith skeleton at Sterkfontein. This important find may resolve some of the questions about where A. africanus fits in the story of human evolution
Working in the Lake Turkana’s region of northern Kenya, a research team led by paleontologist Meave Leakey uncovered in 1999 a cranium and other bone remains of an early human that showed a mixture of features unseen in previous discoveries of early human fossils. The remains were estimated to be 3.5 million years old, and the cranium’s small brain and earhole was similar to those of the earliest humans. Its cheekbone, however, joined the rest of the face in a forward position, and the region beneath the nose opening was flat. These are traits found in later human fossils from around two million years ago, typically those classified in the genus Homo. Noting this unusual combination of traits, researchers named a new genus and species, Kenyanthropus platyops, or ‘flat-faced humans from Kenya.’ Before this discovery, it seemed that only a single early human species, Australopithecus afarensis, lived in East Africa between four million and three million years ago. Yet Kenyanthropus suggests that a diversity of species, including a more humanlike lineage then A. afarensis, lived in this time, just as in most other eras in human prehistory.
The human fossil record is poorly known between three million and two million years ago, which make recent finds from the site of Bouri, Ethiopia, particularly important. From 1996 to 1998, a research team led by Ethiopian paleontologist Berhane Asfaw and American paleontologist Tim White found the skull and other skeletal remains of an early human specimen about 2.5 million years old. The researchers named it Australopithecus garhi; the word garhi means ‘surprise’ in the Afar language. The specimen is unique in having large incisors and molars in combination with an elongated forearm and thighbone. Its powerful arm bones suggest a tree - living ancestry, but its longer legs show the ability to walk upright on the ground. Fossils of A. garhi are associated with some of the oldest known stone tools, along with animal bones that were cut and cracked with tools. It is possible, then, that this species was among the first to make the transition to stone toolmaking and to eating meat and bone marrow from large animals
By 2.7 million years ago the later, robust Australopiths had evolved. These species had what scientists refer to as megadont cheek teeth-wide molars and premolars coated with thick enamel. Their incisors, by contrast, were small. The robusts also had an expanded, flattened, and more vertical face than did gracile Australopiths. This face shape helped to absorb the stresses of strong chewing. On the top of the head, robust Australopiths had a sagittal crest (ridge of bone along the top of the skull from front to back) to which thick jaw muscles attached. The zygomatic arches (which extend back from the cheek bones to the ears), curved out wide from the side of the face and cranium, forming very large openings for the massive chewing muscles to pass through near their attachment to the lower jaw. Together, these traits say that the robust Australopiths chewed their food powerfully and for long periods.
Other ancient animal species that specialized in eating plants, such as some types of wild pigs, had similar adaptations in their facial, dental, and cranial anatomy. Thus, scientists think that the robust Australopiths had a diet consisting partly of tough, fibrous plant foods, such as seed pods and underground tubers. Analyses of microscopic wear on the teeth of some robust australopith specimens appear to support the idea of a vegetarian diet, although chemical studies of fossils suggest that the southern robust species may also have eaten meat.
Scientists originally used the word robust to refer to the late Australopiths out of the belief that they had much larger bodies than did the early, gracile Australopiths. However, further research has revealed that the robust Australopiths stood about the same height and weighed roughly the same amount as Australopithecus afarensis and A. africanus.
The earliest known robust species, Australopithecus aethiopicus, lived in eastern Africa by 2.7 million years ago. In 1985 at West Turkana, Kenya, American paleoanthropologist Alan Walker discovered a 2.5-million-year-old fossil skull that helped to define this species. It became known as the ‘black skull’ because of the colour it had absorbed from minerals in the ground. The skull had a tall sagittal crest toward the back of its cranium and a face that projected far outward from the forehead. A. aethiopicus shared some primitive features with A. afarensis - that is, features that originated in the earlier East African australopith. This may suggest that
A. aethiopicus evolved from A. afarensis.
Australopithecus boisei, the other well - known East African robust australopith, lived over a long period of time, between about 2.3 million and 1.2 million years ago. In 1959 Mary Leakey discovered the original fossil of this species - a nearly complete skull - at the site of Olduvai Gorge in Tanzania. Kenyan-born paleoanthropologist Louis Leakey, husband of Mary, originally named the new species Zinjanthropus boisei (Zinjanthropus translates as ‘East African man’). This skull - dating from 1.8 million years ago - has the most specialized features of all the robust species. It has a massive, wide and dished-in face capable of withstanding extreme chewing forces, and molars four times the size of those in modern humans. Since the discovery of Zinjanthropus, now recognized as an australopith, scientists have found great numbers of A. boisei fossils in Tanzania, Kenya, and Ethiopia.
The southern robust species, called Australopithecus robustus, lived between about 1.8 million and 1.3 million years ago in the Transvaal, the same region that was home to A. africanus. In 1938 Robert Broom, who had found many A. africanus fossils, bought a fossil jaw and molar that looked distinctly different from those in A. africanus. After finding the site of Kromdraai, from which the fossil had come, Broom collected many more bones and teeth that together convinced him to name a new species, which he called Paranthropus robustus (Paranthropus meaning ‘beside man’). Later scientists dated this skull at about 1.5 million years old. In the late 1940's and 1950 Broom discovered many more fossils of this species at the Transvaal site of Swartkrans.
Paleoanthropologists believe that the eastern robust species, A. aethiopicus and A. boisei, may have evolved from an early australopith of the same region, perhaps A. afarensis. According to this view, A. africanus gave rise only to the southern species A. robustus. Scientists refer to such a case - in which two or more independent species evolve similar characteristics in different places or at different times - as parallel evolution. If parallel evolution occurred in Australopiths, the robust species would make up two separate branches of the human family tree.
The last robust Australopiths died out about 1.2 million years ago. At about this time, climate patterns around the world entered a period of fluctuation, and these changes may have reduced the food supply on which robusts depended. Interaction with larger-brained members of the genus Homo, such as Homo erectus, may also have contributed to the decline of late Australopiths, although no compelling evidence exists of such direct contact. Competition with several other species of plant-eating monkeys and pigs, which thrived in Africa at the time, may have been an even more important factor. Nevertheless, the reason that the robust Australopiths became extinct after flourishing for such a long time is not yet known for sure.
Scientists have several ideas about why Australopiths first split off from the apes, initiating the course of human evolution. Virtually all hypotheses suggest that environmental change was an important factor, specifically in influencing the evolution of Bipedalism. Some well - established ideas about why humans first evolved include (1) the savanna hypothesis, (2) the woodland-mosaic hypothesis, and (3) the variability hypothesis.
The global climate cooled and became drier between eight million and five million years ago, near the end of the Miocene Epoch. According to the savanna hypothesis, this climate change broke up and reduced the area of African forests. As the forests shrunk, an ape population in eastern Africa became separated from other populations of apes in the more heavily forested areas of western Africa. The eastern population had to adapt to its drier environment, which contained larger areas of grassy savanna.
The expansion of dry terrain favoured the evolution of terrestrial living, and made it more difficult to survive by living in trees. Terrestrial apes might have formed large social groups in order to improve their ability to find and collect food and to fend off predators - activities that also may have required the ability to communicate well. The challenges of savanna life might also have promoted the rise of tool use, for purposes such as scavenging meat from the kills of predators. These important evolutionary changes would have depended on increased mental abilities and, therefore, may have correlated with the development of larger brains in early humans.
Critics of the savanna hypothesis argue against it on several grounds, but particularly for two reasons. First, discoveries by a French scientific team of australopith fossils in Chad, in Central Africa, suggest that the environments of East Africa may not have been fully separated from those farther west. Second, recent research suggests that open savannas were not prominent in Africa until sometime after two million years ago.
Criticism of the savanna hypothesis has spawned alternative ideas about early human evolution. The woodland-mosaic hypothesis proposes that the early Australopiths evolved in patchily wooded areas - a mosaic of woodland and grassland - that offered opportunities for feeding both on the ground and in the trees, and that ground feeding favoured Bipedalism.
The variability hypothesis suggests that early Australopiths experienced many changes in environment and ended up living in a range of habitats, including forests, open-canopy woodlands, and savannas. In response, their populations became adapted to a variety of surroundings. Scientists have found that this range of habitats existed at the time when the early Australopiths evolved. So the development of new anatomical characteristics, - particularly Bipedalism -combined with an ability to climb trees, may have given early humans the versatility to live in a variety of habitats.
Bipedalism in early humans would have enabled them to travel efficiently over long distances, giving them an advantage over quadrupedal apes in moving across barren open terrain between groves of trees. In addition, the earliest humans continued to have the advantage from their ape ancestry of being able to escape into the trees to avoid predators. The benefits of both Bipedalism and agility in the trees may explain the unique anatomy of Australopiths. Their long, powerful arms and curved fingers probably made them good climbers, while their pelvis and lower limb structure were reshaped for upright walking people belong to the genus Homo, which first evolved at least 2.3 million to 2.5 million years ago. The earliest members of this genus differed from the Australopiths in at least one important respect - they had larger brains than did their predecessors.
The evolution of the modern human genus can be divided roughly into three periods: early, middle, and late. Species of early Homo resembled gracile Australopiths in many ways. Some early Homo species lived until possibly 1.6 million years ago. The period of middle Homo began perhaps between two million and 1.8 million years ago, overlapping with the end of early Homo. Species of middle Homo evolved an anatomy much more similar to that of modern humans but had comparatively small brains. The transition from middle to late Homo probably occurred sometime around 200,000 years ago. Species of late Homo evolved large and complex brains and eventually language. Culture also became an increasingly important part of human life during the most recent period of evolution.
The origin of the genus Homo has long intrigued paleoanthropologists and prompted much debate. One of several known species of Australopiths, or one not yet discovered, could have given rise to the first species of Homo. Scientists also do not know exactly what factors favoured the evolution of a larger and more complex brain - the defining physical trait of modern humans.
Louis Leakey originally argued that the origin of Homo related directly to the development of toolmaking - specifically, the making of stone tools. Toolmaking requires certain mental skills and fine hand manipulation that may exist only in members of our own genus. Indeed, the name Homo habilis (meaning ‘handy man’) refer directly to the making and use of tools
However, several species of Australopiths lived at the same time as early Homo, making it unclear which species produced the earliest stone tools. Recent studies of australopith hand bones have suggested that at least one of the robust species, Australopithecus robustus, could have made tools. In addition, during the 1960's and 1970's researchers first observed that some nonhuman primates, such as chimpanzees, make and use tools, suggesting that Australopiths and the apes that preceded them probably also made some kinds of tools.
According to some scientists, however, early Homo probably did make the first stone tools. The ability to cut and pound foods would have been most useful to these smaller-toothed humans, whereas the robust Australopiths could chew even very tough foods. Furthermore, early humans continued to make stone tools similar to the oldest known kinds for a time long after the gracile Australopiths died out. Some scientists think that a period of environmental cooling and drying in Africa set the stage for the evolution of Homo. According to this idea, many types of animals suited to the challenges of a drier environment originated during the period between about 2.8 million and 2.4 million years ago, including the first species of Homo.
A toolmaking human might have had an advantage in obtaining alternative food sources as vegetation became sparse in increasingly dry environments. The new foods might have included underground roots and tubers, as well as meat obtained through scavenging or hunting. However, some scientists disagree with this idea, arguing that the period during which Homo evolved fluctuated between drier and wetter conditions, rather than just becoming dry. In this case, the making and use of stone tools and an expansion of the diet in early Homo - as well as an increase in brain size - may all have been adaptations to unpredictable and fluctuating environments. In either case, more scientific documentation is necessary to support strongly or refute the idea that early Homo arose as part of a larger trend of rapid species extinction and the evolution of many new species during a period of environmental change.
Paleoanthropologists generally recognize two species of early Homo-Homo habilis and H. rudolfensis (although other species may also have existed). The record is unclear because most of the early fossils that scientists have identified as species of Homo, - rather than robust Australopiths who lived at the same time occur as isolated fragments. In many places, only teeth, jawbones, and pieces of skull - without any other skeletal remains - suggest that new species of smaller-toothed humans had evolved as early as 2.5 million years ago. Scientists cannot always tell whether these fossils belong to late-surviving gracile Australopiths or early representatives of Homo. The two groups resemble each other because Homo likely descended directly from a species of gracile australopith.
In the early 1960's, at Olduvai Gorge, Tanzania, Louis Leakey, British primate researcher John Napier, and South African paleoanthropologist Philip Tobias discovered a group of early human fossils that showed a cranial capacity from 590 to 690 cu. cm. (36 to 42 cu. in.). Based on this brain size, which was completely above the range of that in known Australopiths, the scientists argued that a new genus, Homo, and a new species, Homo habilis, should be recognized. Other scientists questioned whether this amount of brain enlargement was sufficient for defining a new genus, and even whether H. habilis were different from Australopithecus africanus, as the teeth of the two species look similar. However, scientists now widely accept both the genus and species names designated by the Olduvai team.
H. habilis lived in eastern and possibly southern Africa between about 1.9 million and 1.6 million years ago, and maybe as early as 2.4 million years ago. Although the fossils of this species somewhat resemble those of Australopiths, H. habilis had smaller and narrower molar teeth, premolar teeth, and jaws than did its predecessors and contemporary robust Australopiths.
A fragmented skeleton of a female from Olduvai shows that she stood only about one m. (3.3 ft.) tall, and the ratio of the length of her arms to her legs was greater than that in the australopith Lucy. At least in the case of this individual, therefore, H. habilis had very apelike body proportions. However, H. habilis had more modern-looking feet and hands capable of producing tools. Some of the earliest stone tools from Olduvai have been found with H. habilis fossils, suggesting that this species made and used the tools at this site.
Scientists began to notice a high degree of variability in body size as they discovered more early Homo fossils. This could have suggested that H. habilis had a large amount of sexual dimorphism. For instance, the Olduvai female skeleton was dwarfed in comparison with other fossils - exemplified by a sizable early Homo cranium from East Turkana in northern Kenya. However, the differences in size actually exceeded those expected between males and females of the same species, and this finding later helped convince scientists that another species of early Homo had lived in eastern Africa.
This second species of early Homo was given the name Homo rudolfensis, after Lake Rudolf (now Lake Turkana). The best - known fossils of H. rudolfensis come from the area surrounding this lake and date from about 1.9 million years ago. Paleoanthropologists have not determined the entire time range during which H. rudolfensis may have lived.
This species had a larger face and body than did H. habilis. The cranial capacity of H. rudolfensis averaged about 750 cu. cm. (46 cu. in.). Scientists need more evidence to know whether the brain of H. rudolfensis in relation to its body size was larger than that proportion in H. habilis. A larger brain-to-body-size ratio can suggest increased mental abilities. H. rudolfensis also had large teeth, approaching the size of those in robust Australopiths. The discovery of even a partial fossil skeleton would reveal whether this larger form of early Homo had apelike or more modern body proportions. Scientists have found several modern-looking thighbones that date from between two million and 1.8 million years ago and may belong to H. rudolfensis. These bones suggest a body size of 1.5 m. (5 ft.) and 52 kg. (114 lb.).
By about 1.9 million years ago, the period of middle Homo had begun in Africa. Until recently, paleoanthropologists recognized one species in this period, Homo erectus. Many now recognize three species of middle Homo: H. ergaster, H. erectus, and H. heidelbergensis. However, some still think H. ergaster is an early African form of H. erectus, or that H. heidelbergensis is a late form of H. erectus.
The skulls and teeth of early African populations of middle Homo differed subtly from those of later H. erectus populations from China and the island of Java in Indonesia. H. ergaster makes a better candidate for an ancestor of the modern human line because Asian H. erectus has some specialized features not seen in some later humans, including our own species. H. heidelbergensis has similarities to both H. erectus and the later species H. neanderthalensis, although it may have been a transitional species between middle Homo and the line to which modern humans belong.
Homo ergaster probably first evolved in Africa around two million years ago. This species had a rounded cranium with a brain size of between 700 and 850 cu. cm. (49 to 52 cu. in.), a prominent brow ridge, small teeth, and many other features that it shared with the later H. erectus. Many paleoanthropologists consider H. ergaster a good candidate for an ancestor of modern humans because it had several modern skull features, including relatively thin cranial bones. Most H. ergaster fossils come from the time range of 1.8 million to 1.5 million years ago.
The most important fossil of this species yet found is a nearly complete skeleton of a young male from West Turkana, Kenya, which dates from about 1.55 million years ago. Scientists determined the sex of the skeleton from the shape of its pelvis. They also found out from patterns of tooth eruption and bone growth that the boy had died when he was between nine and 12 years old.
The Turkana boy, as the skeleton is known, had elongated leg bones and arm, leg, and trunk proportions of which essentially match those of a modern human, in sharp contrast with the apelike proportions H. habilis and Australopithecus afarensis. He appears to have been quite tall and slender. Scientists estimate that, had he grown into adulthood, the boy would have reached a height of 1.8 m. (6 ft.) and a weight of 68 kg (150 lb.). The anatomy of the Turkana boy shows that H. ergaster was particularly well adapted for walking and perhaps for running long distances in a hot environment
(a tall and slender body dissipates heat well) but not for any significant amount of tree climbing.
The oldest humanlike fossils outside of Africa have also been classified as H. ergaster, dated around 1.75 million year’s old. These finds, from the Dmanisi site in the southern Caucasus Mountains of Georgia, consist of several crania, jaws, and other fossilized bones. Some of these are strikingly like East African H. ergaster, but others are smaller or larger than H. ergaster, suggesting a high degree of variation within a single population.
H. ergaster, H. rudolfensis, and H. habilis, in addition to possibly two robust Australopiths, all might have coexisted in Africa around 1.9 million years ago. This finding goes against a traditional paleoanthropological view that human evolution consisted of a single line that evolved progressively over time, - an australopith species followed by early Homo, then middle Homo, and finally H. sapiens. It appears that periods of species diversity and extinction have been common during human evolution, and that modern H. sapiens has the rare distinction of being the only living human species today.
Although H. ergaster appears to have coexisted with several other human species, they probably did not interbreed. Mating rarely succeeds between two species with significant skeletal differences, such as H. ergaster and H. habilis. Many paleoanthropologists now believe that H. ergaster descended from an earlier population of Homo - perhaps one of the two known species of early Homo - and that the modern human line descended from H. ergaster.
Paleoanthropologists now know that humans first evolved in Africa and lived only on that continent for a few million years. The earliest human species known to have spread in large numbers beyond the African continent was first discovered in Southeast Asia. In 1891 Dutch physician Eugne Dubois found the cranium of an early human on the Indonesian island of Java. He named this early human Pithecanthropus erectus, or ‘erect ape-man.’Today paleoanthropologists refer to this species as Homo erectus.
H. erectus appears to have evolved in Africa from earlier populations of H. ergaster, and then spread to Asia sometime between 1.8 million and 1.5 million years ago. The youngest known fossils of this species, from the Solo River in Java, may date from about 50,000 years ago (although that dating is controversial). So
H. erectus was a very successful species - both widespread, having lived in Africa and much of Asia, and long - lived, having survived for possibly more than 1.5 million years.
Homo erectus had a low and rounded braincase that was elongated from front to back, a prominent brow ridge, and adult cranial capacity of 800 to 1,250 cu. cm. (50 to 80 cu. in.), an average twice that of the Australopiths. Its bones, including the cranium, were thicker than those of earlier species. Prominent muscle markings and thick, reinforced areas on the bones of H. erectus indicate that its body could withstand powerful movements and stresses. Although it had much smaller teeth than did the Australopiths, it had a heavy and strong jaw.
In the 1920's and 1930's German anatomist and physical anthropologist Franz Weidenreich excavated the most famous collections of H. erectus fossils from a cave at the site of Zhoukoudian (Chou - k’ou - tien), China, near Beijing (Peking). Scientists dubbed these fossil humans Sinanthropus pekinensis, or Peking Man, but others later reclassified them as H. erectus. The Zhoukoudian cave yielded the fragmentary remains of more than 30 individuals, ranging from about 500,000 to 250,000 years old. These fossils were lost near the outbreak of World War II, but Weidenreich had made excellent casts of his finds. Further studies at the cave site have yielded more H. erectus remains.
Other important fossil sites for this species in China include Lantian, Yuanmou, Yunxian, and Hexian. Researchers have also recovered many tools made by H. erectus in China at sites such as Nihewan and Bose, and other sites of similar age (at least one million to 250,000 years old).
Ever since the discovery of Homo erectus, scientists have debated whether this species was a direct ancestor of later humans, including H. sapiens. The last populations of H. erectus - such as those from the Solo River in Java, - may have lived as recently as 50,000 years ago, at the same time as did populations of H. sapiens. Modern humans could not have evolved from these late populations of H. erectus, a much more primitive type of human. However, earlier East Asian populations could have given rise to H. sapiens.
Many paleoanthropologists believe that early humans migrated into Europe by 800,000 years ago, and that these populations were not Homo erectus. A growing number of scientists refer to these early migrants into Europe - who predated both Neanderthals and H. sapiens in the region, - as H. heidelbergensis. The species name comes from a 500,000-year-old jaw found near Heidelberg, Germany.
Scientists have found few human fossils in Africa for the period between 1.2 million and 600,000 years ago, during which
H. heidelbergensis or its ancestors first migrated into Europe. Populations of H. ergaster (or possibly H. erectus) appear to have lived until at least 800,000 years ago in Africa, and possibly until 500,000 years ago in northern Africa. When these populations disappeared, other massive-boned and larger-brained humans.
-possibly H. heidelbergensis- appears to have replaced them. Scientists have found fossils of these stockier humans at sites in Bodo, Ethiopia; Saldanha (also known as Elandsfontein), South Africa; Ndutu, Tanzania; and Kabwe, Zimbabwe
Scientists have come up with at least three different interpretations of these African fossils. Some scientists place the fossils in the species H. heidelbergensis and think that this species gave rise to both the Neanderthals (in Europe) and H. sapiens (in Africa). Others think that the European and African fossils belong to two distinct species, and that the African populations that, in this view, was not H. heidelbergensis but a separate species gave rise to H. sapiens. Yet other scientists advocate a long-head view that
H. erectus and H. sapiens belong to a single evolving lineage, and that the African fossils belong in the category of archaic H. sapiens (archaic meaning not fully anatomically modern)
The fossil evidence does not clearly favour any of these three interpretations over another. A growing number of fossils from Asia, Africa, and Europe have features that are intermediate between early
H. ergaster and H. sapiens. This kind of variation makes it hard to decide how to identify distinct species and to find out which group of fossils represents the most likely ancestor of later humans.
Humans evolved in Africa and lived only there for as long as four million years or more, so scientists wonder what finally triggered the first human migration out of Africa (a movement that coincided with the spread of early human populations throughout the African continent). The answer to this question depends, in part, on knowing exactly when that first migration occurred. Some studies claim that site in Asia and Europe contain crude stone tools and fossilized fragments of humanlike teeth that date from more than 1.8 million years ago. Although these claims remain unconfirmed, small populations of humans may have entered Asia before 1.8 million years ago, followed by a more substantial spread between 1.6 million and one million years ago. Early humans reached northeastern Asia by around 1.4 million years ago, inhabiting a region close to the perpetually dry deserts of northern China. The first major habitation of central and western Europe, on the other hand, does not appear to have occurred until between one million and 500,000 years ago.
Scientists once thought that advances in stone tools could have enabled early humans such as Homo erectus to move into Asia and Europe, perhaps by helping them to obtain new kinds of food, such as the meat of large mammals. If African human populations had developed tools that allowed them to hunt large game effectively, they would have had a good source of food wherever they went. In this view, humans first migrated into Eurasia based on a unique cultural adaptation.
By 1.5 million years ago, early humans had begun to make new kinds of tools, which scientists call Acheulean. Common Acheulean tools included large hand axes and cleavers. While these new tools might have helped early humans to hunt, the first known Acheulean tools in Africa date from later than the earliest known human presence in Asia. Also, most East Asian sites more than 200,000 years old contains only simply shaped cobble and flake tools. In contrast, Acheulean tools were more finely crafted, larger, and more symmetrical. Thus, the earliest settlers of Eurasia did not have a true Acheulean technology, and advances in toolmaking alone cannot explain the spread out of Africa.
Another possibility is that the early spread of humans to Eurasia was not unique, but parts of a wider migration of meat -eating animals, such as lions and hyenas. The human migration out of Africa occurred during the early part of the Pleistocene Epoch, between 1.8 million and 780,000 years ago. Many African carnivores spread to Eurasia during the early Pleistocene, and humans could have moved along with them. In this view, H. erectus seem one of many meat-eating species to expand into Eurasia from Africa, rather than a uniquely adapted species. Relying on meat as a primary food source might have allowed many meat - eating species, including humans, to move through many different environments without having to learn about unfamiliar and potentially poisonous plants quickly.
However, the migration of humans to eastern Asia may have occurred gradually and through lower latitudes and environments similar to those of Africa. If East African populations of H. erectus moved at only 1.6 km. (1 mi.) every 20 years, they could have reached Southeast Asia in 150,000 years. Over this amount of time, humans could have learned about and begun relying on edible plant foods. Thus, eating meat may not have played a crucial role in the first human migrations to new continents. Careful comparison of animal fossils, stone tools, and early human fossils from Africa, Asia, and Europe will help scientists better to find what factors motivated and allowed humans to venture out of Africa for the first time.
The origin of our own species, Homo sapiens, is one of the most hotly debated topics in Paleoanthropology. This debate centres on whether or not modern humans have a direct relationship to
H. erectus or to the Neanderthals, and to a great extent is acknowledged of the more modern group of humans who evolved within the past 250,000 years. Paleoanthropologists commonly use the term anatomically modern Homo sapiens to distinguish people of today from these similar predecessors.
Traditionally, paleoanthropologists classified as Homo sapiens any fossil human younger than 500,000 years old with a braincase larger than that of H. erectus. Thus, many scientists who believe that modern humans descend from a single line dating back to H. erectus use the name archaic Homo sapiens to refer to a wide variety of fossil humans that predate anatomically modern H. sapiens. The archaic term denotes a set of physical features typical of Neanderthals and other species of late Homo before modern Homo sapiens. These features include a combination of a robust skeleton, a large but low braincase (positioned somewhat behind, rather than over, the face), and a lower jaw lacking a prominent chin. In this sense, Neanderthals are sometimes classified as a subspecies of archaic H. sapiens-H. neanderthalensis. Other scientists think that the variation in archaic fossils actually falls into clearly identifiable sets of traits, and that any type of human fossil exhibiting a unique set of traits should have a new species name. According to this view, the Neanderthals belong to their own species, H. neanderthalensis.
In the past, scientists claimed that Neanderthals differed greatly from modern humans. However, the basis for this claim came from a faulty reconstruction of a Neanderthal skeleton that showed it with bent knees and a slouching gait. This reconstruction gave the common but mistaken impression that Neanderthals were dim - witted brutes who lived a crude lifestyle. On the contrary, Neanderthals, like the species that preceded them, walked fully upright without a slouch or bent knees. In addition, their cranial capacity was quite large at about 1,500 cu. cm. (about 90 cu. in.), larger on average than that of modern humans. (The difference probably relates to the greater muscle mass of Neanderthals as compared with modern humans, which usually correlates with a larger brain size.).
Compared with earlier humans, Neanderthals had a high degree of cultural sophistication. They appear to have performed symbolic rituals, such as the burial of their dead. Neanderthal fossils - including a number of fairly complete skeletons, - are quite common compared with those of earlier forms of Homo, in part because of the Neanderthal practice of intentional burial. Neanderthals also produced sophisticated types of stone tools known as Mousterian, which involved creating blanks (rough forms) from which several types of tools could be made.
Along with many physical similarities, Neanderthals differed from modern humans in several ways. The typical Neanderthal skull had a low forehead, a large nasal area (suggesting a large nose), a forward-projecting nasal and cheek region, a prominent brow ridge with a bony arch over each eye, a nonprojecting chin, and obvious space behind the third molar (in front of the upward turn of the lower jaw).
Neanderthals were heavily built and had prominently-boned skeleton body structures than do modern humans. Other Neanderthal skeletal features included a bowing of the limb bones in some individuals, broad scapulae (shoulder blades), hip joints turned outward, a long and thin pubic bone, short lower leg and arm bones on the upper bones, and large surfaces on the joints of the toes and limb bones. Together, these traits made a powerful, compact body of short stature of males averaged 1.7 m. (5 ft. 5 in.) tall and 84 kg. (185 lb.), and females averaged 1.5 m. (5 ft.) tall and 80 kg. (176 lb.). The short, stocky build of Neanderthals conserved heat and helped them withstand extremely cold conditions that prevailed in temperate regions beginning about 70,000 years ago. The last known Neanderthal fossils come from western Europe and date from approximately 36,000 years ago.
At the same time as Neanderthal populations grew in number in Europe and parts of Asia, other populations of nearly modern humans arose in Africa and Asia. Scientists also commonly refer to these fossils, which are distinct from but similar to those of Neanderthals, as archaic. Fossils from the Chinese sites of Dali, Maba, and Xujiayao display the long, low cranium and large face typical of archaic humans, yet they also have features similar to those of modern people in the region. At the cave site of Jebel Irhoud, Morocco, scientists have found fossils with the long skull typical of archaic humans but also the modern traits of a somewhat higher forehead and flatter midface. Fossils of humans from East African sites older than 100,000 years, such as Ngaloba in Tanzania and Eliye Springs in Kenya, - also seem to show a mixture of archaic and modern traits.
The oldest known fossils that possess skeletal features typical of modern humans date from between 130,000 and 90,000 years ago. Several key features distinguish the skulls of modern humans from those of archaic species. These features include a much smaller brow ridge, if any; a globe-shaped braincase; and a flat or only projecting face of reduced size, located under the front of the braincase. Among all mammals, only humans have a face positioned directly beneath the frontal lobe (forward-most area) of the brain. As a result, modern humans tend to have a higher forehead than did Neanderthals and other archaic humans. The cranial capacity of modern humans ranges from about 1,000 to 2,000 cu. cm. (60 to 120 cu. in.), with the average being about 1,350 cu. cm. (80 cu. in.).
Scientists have found both fragmentary and nearly complete cranial fossils of early anatomically modern Homo sapiens from the sites of Singha, Sudan; Omo, Ethiopia; Klasies River Mouth, South Africa; and Skhū-Cave, Israel. Based on these fossils, many scientists conclude that modern H. sapiens had evolved in Africa by 130,000 years ago and started spreading to diverse parts of the world beginning on a route through the Near East sometime before 90,000 years ago.
Paleoanthropologists are engaged in an ongoing debate about where modern humans evolved and how they spread around the world. Differences in opinion rest on the question of whether the evolution of modern humans took place in a small region of Africa or over a broad area of Africa and Eurasia. By extension, opinions differ as to whether modern human populations from Africa displaced all existing populations of earlier humans, eventually resulting in their extinction.
Those, who think modern humans originated exclusively in Africa, and then spread around the world support what is known as the out of Africa hypothesis. Those who think modern humans evolved over a large region of Eurasia and Africa support the so-called multiregional hypothesis.
Researchers have conducted many genetic studies and carefully assessed fossils to figure out which of these hypotheses agrees more with scientific evidence. The results of this research do not entirely confirm or reject either one. Therefore, some scientists think a compromise between the two hypotheses is the best explanation. The debate between these views has implications for how scientists understand the concept of race in humans. The dubious question that raises an augmented curiously of itself is to whether the physical differences among modern humans evolved deep in the past or relatively recent, in which is accorded to the out of Africa hypothesis. It is also known as the replacement hypothesis, by which early populations of modern humans out from Africa migrated to other regions and entirely replaced existing populations of archaic humans. The replaced populations would have included the Neanderthals and any surviving groups of Homo erectus. Supporters of this view note that many modern human skeletal traits evolved relatively recently - within the past 200,000 years or so, - suggesting a single, common origin. Additionally, the anatomical similarities shared by all modern human populations far outweigh those shared by premodern and modern humans within particular geographic regions. Furthermore, biological research suggested that most new species of organisms, including mammals, arose from small, geographically isolated populations.
According to the multiregional hypothesis, also known as the continuity hypothesis, the evolution of modern humans began when Homo erectus spread throughout much of Eurasia around one million years ago. Regional populations retained some unique anatomical features for hundreds of thousands of years, but they also mated with populations from neighbouring regions, exchanging heritable traits with each other. This exchange of heritable traits is known as gene flow.
Through gene flow, populations of H. erectus passed on a variety of increasingly modern characteristics, such as increases in brain size, across their geographic range. Gradually this would have resulted in the evolution of more modern looking humans throughout Africa and Eurasia. The physical differences among people today, then, would result from hundreds of thousands of years of regional evolution. This is the concept of continuity. For instance, modern East Asian populations have some skull features that scientists also see in H. erectus fossils from that region.
Noticeably critics of the multi-regional hypothesis claim that it wrongly advocates a scientific belief in race and could be used to encourage racism. Supporters of the theory point out, however, that their position does not imply that modern races evolved in isolation from each other, or that racial differences justify racism. Instead, the theory holds that gene flow linked different populations together. These links allowed progressively more modern features, no matter where they arose, to spread from region to region and eventually become universal among humans.
Scientists have weighed the out of Africa and multi-regional hypotheses against both genetic and fossil evidence. The results do not unanimously support either one, but weigh more heavily in favour of the out of Africa hypothesis.
Geneticists have studied the amount of difference in the DNA (deoxyribonucleic acid) of different populations of humans. DNA is the molecule that contains our heritable genetic code. Differences in human DNA result from mutations in DNA structure. Mutations may result from exposure to external elements such as solar radiation or certain chemical compounds, while others occur naturally at random.
Geneticists have calculated rates at which mutations can be expected to occur over time. Dividing the total number of genetic differences between two populations by an expected rate of mutation provides an estimate of the time when the two gave cause to be joined of a common ancestor. Many estimates of evolutionary ancestry rely on studies of the DNA in cell structures called mitochondria. This DNA is referred to as mtDNA (mitochondrial DNA). Unlike DNA from the nucleus of a cell, which codes for most of the traits an organism inherits from both parents, mtDNA inheritance passes only from a mother to her offspring. MtDNA also accumulates mutations about ten times faster than does DNA in the cell nucleus (the location of most DNA). The structure of mtDNA changes so quickly that scientists can easily measure the differences between one human population and another. Two closely related populations should have only minor differences in their mtDNA. Conversely, two very distantly related populations should have large differences in their mtDNA.
MtDNA research into modern human origins has produced two major findings. First, the entire amount of variation in mtDNA across human populations is small in comparison with that of other animal species. This significance, in that all human mtDNA originated from a single ancestral lineage - specifically, a single female - recently and has been mutating ever since. Most estimates of the mutation rate of mtDNA suggest that this female ancestor lived about 200,000 years ago. In addition, the mtDNA of African populations varies more than that of peoples in other continents. This suggests that the mtDNA of African populations have proven in identifying their place of a value on a longer time than it has in populations over any other region. In that all living people inherited their mtDNA from one woman in Africa, who is sometimes called the Mitochondrial Eve, in addition geneticists and anthropologists have concluded from this evidence that modern humans originated in a small population in Africa and spread out from there.
MtDNA studies have weaknesses, however, including the following four. First, the estimated rate of mtDNA mutation varies from study to study, and some estimates put the date of origin closer to 850,000 years ago, the time of Homo erectus. Second, mtDNA makes up a small part of the total genetic material that humans inherit. The rest of our genetic material - about 400,000 times more than the amount of mtDNA, - came from many individuals living at the time of the African Eve, conceivably from many different regions. This intermittent interval of which time modern mtDNA began to diversify does not necessarily coincide with the origin of modern human biological traits and cultural abilities. Fourth, the smaller amount of modern mtDNA diversity outside of Africa could result from times when European and Asian populations declined in numbers, perhaps due to climate changes.
Regardless of these criticisms, many geneticists continue to favour the out of Africa hypothesis of modern human origins. Studies of nuclear DNA also suggest an African origin for a variety of genes. Furthermore, in a remarkable series of studies in the late 1990s, scientists recovered mtDNA from the first Neanderthal fossil found in Germany and two other Neanderthal fossils. In each case, the mtDNA does not closely match that of modern humans. This finding suggests that at least some Neanderthal populations had diverged from the line to modern humans by 500,000 to 600,000 years ago, and the depriving of an augmented potential of possible occurrence is apprehensibly actualized, and which can be known as having an existence as categorized in virtue been no attributed thing but some substantiation by a form of something exacted to have happened. Also to suggest that Neanderthals represent a separate species from modern H. sapiens. In another study, however, mtDNA extracted from a 62,000-year-old Australian H. sapiens fossil was found to differ significantly from modern human mtDNA, suggesting a much wider range of mtDNA variation within H. sapiens than was previously believed. According to the Australian researchers, this finding lends support to the multiregional hypothesis because it shows that different populations of H. sapiens, possibly including Neanderthals, could have evolved independently in different parts of the world.
As with genetic research, fossil evidence also does not entirely support or refute either of the competing hypotheses of modern human origins. However, many scientists see the balance of evidence favouring an African origin of modern H. sapiens within the past 200,000 years. The oldest known modern-looking skulls come from Africa and date from perhaps 130,000 years ago. The next oldest comes from the Near East, where they date from about 90,000 years ago. Fossils of modern humans in Europe do not exist from before about 40,000 years ago. In addition, the first modern humans in Europe - often referred to as Cro-Magnon people had elongated lower leg bones, as did African populations that were adapted too warm, tropical climates. This suggests that populations from warmer regions replaced those in colder European regions, such as the Neanderthals.
Fossils also show that populations of modern humans lived at the same time and in the same regions as did populations of Neanderthals and Homo erectus, but that each retained its distinctive physical features. The different groups overlapped in the Near East and Southeast Asia for between about 30,000 and 50,000 years. The maintenance of physical differences for this amount of time implies that archaically and modern humans could either not or generally did not interbreed. To some scientists, this also means that the Neanderthals belong to a separate species, H. neanderthalensis, and that migratory populations of modern humans entirely replaced archaic humans in both Europe and eastern Asia.
On the other hand, fossils of archaic and modern humans in some regions show continuity in certain physical characteristics. These similarities may indicate multi-regional evolution. For example, both archaic and modern skulls of eastern Asia have flatter cheek and nasal areas than do skulls from other regions. By contrast, the same parts of the face project forward in the skulls of both archaic and modern humans of Europe. Assuming that these traits were influenced primarily by genetic inheritance rather than environmental factors, archaic humans may have given rise to modern humans in some regions or at least interbred with migrant modern-looking humans.
Each of the competing major hypotheses of modern human origins has its strengths and weaknesses. Genetic evidence appears to support the out of Africa hypothesis. In the western half of Eurasia and in Africa, this hypothesis also seems the better explanation, particularly in regard to the apparent replacement of Neanderthals by modern populations. At the same time, the multi-regional hypothesis appears to explain some of the regional continuity found in East Asian populations.
Therefore, many paleoanthropologists advocate a theory of modern human origins that combines elements of the out of Africa and the changing regional hypotheses. Humans with modern features may have first come forth in Africa or come together there as a result of gene flow with populations from other regions. These African populations may then have replaced archaic humans in certain regions, such as western Europe and the Near East. Nevertheless, elsewhere, - especially in East Asia- gene flow may have occurred among local populations of archaic and modern humans, resulting in distinct and enduring regional characteristics.
All three of these views - the two competing positions and the compromise; acknowledge the strong biological unity of all people. In the multi-regional hypothesis, this unity results from hundreds of thousands of years of continued gene flow among all human populations. According to the out of Africa hypothesis, on the other hand, similarities among all living human populations result from a recent common origin. The compromise position accepts both of these as reasonable and compatible explanations of modern human origins.
The story of human evolution is as much about the development of cultural behaviour as it is about changes in physical appearance. The term culture, in anthropology, traditionally refers to all human creations and activities governed by social customs and rules. It includes elements such as technology, language, and art. Human cultural behaviour depends on the social transfer of information from one generation to the next, which it depends on a sophisticated system of communication, such as language.
The term culture has often been used to distinguish the behaviour of humans from that of other animals. However, some nonhuman animals also appear to have forms of learned cultural behaviours. For instance, different groups of chimpanzees use different techniques to capture termites for food using sticks. Also, in some regions chimps use stones or pieces of wood for cracking open nuts. Chimps in other regions do not practice this behaviour, although their forests have similar nut trees and materials for making tools. These regional differences resemble traditions that people pass from generation to generation. Traditions are a fundamental aspect of culture, and paleoanthropologists assume that the earliest humans also had some types of traditions.
However, modern humans differ from other animals, and probably many early human species, in that they actively teach each other and can pass on and accumulate unusually large amounts of knowledge. People also have a uniquely long period of learning before adulthood, and the physical and mental capacity for language. Language of all forms, spoken, signed, and written in provides a medium for communicating vast amounts of information, much more than any other animal appears to be able to transmit through gestures and vocalizations.
Scientists have traced the evolution of human cultural behaviour through the study of archaeological artifacts, such as tools, and related evidence, such as the charred remains of cooked food. Artifacts show that throughout much of human evolution, culture has developed slowly. During the Palaeolithic, or early Stone Age, basic techniques for making stone tools changed very little for periods of well more than a million years.
Human fossils also provide information about how culture has evolved and what effects it has had on human life. For example, over the past 30,000 years, the basic anatomy of humans has undergone only one prominent change: The bones of the average human skeleton have become much smaller and thinner. Innovations in the making and use of tools and in obtaining food.- results of cultural evolution may have led to more efficient and less physically taxing lifestyles, and thus caused changes in the skeleton.
Paleoanthropologists and archaeologists have studied many topics in the evolution of human cultural behaviour. These have included the evolution of (1) social life; (2) subsistence (the acquisition and production of food); (3) the making and using of tools; (4) environmental adaptation; (5) symbolic thought and its expression through language, art, and religion; and (6) the development of agriculture and the rise of civilizations.
One of the first physical changes in the evolution of humans from apes - a decrease in the size of male canine teeth - also indicates a change in social relations. Male apes sometimes use their large canines to threaten (or sometimes fight with) other males of their species, usually over access to females, territory, or food. The evolution of small canines in Australopiths implies that males had either developed other methods of threatening each other or become more cooperative. In addition, both male and female Australopiths had small canines, indicating a reduction of sexual dimorphism from that in apes. Yet, although sexual dimorphism in canine size decreased in Australopiths, males were still much larger than females. Thus, male Australopiths might have competed aggressively with each other based on sheer size and strength, and the social life of humans may not have differed much from that of apes until later times.
Scientists believe that several of the most important changes from apelike to characteristically human social life occurred in species of the genus Homo, whose members show even less sexual dimorphism. These changes, which may have occurred at different times, included (1) prolonged maturation of infants, including an extended period during which they required intensive care from their parents; (2) special bonds of sharing and exclusive mating between particular males and females, called pair-bonding; and (3) the focus of social activity at a home base, a safe refuge in a special location known to family or group members.
Humans, who have a large brain, have a prolonged period of infant development and childhood because the brain takes a long time too mature. Since the australopith brain was not much larger than that of a chimp, some scientists think that the earliest humans had a more apelike rate of growth, which is far more rapid than that of modern humans. This view is supported by studies of australopith fossils looking at tooth development - a good indicator of overall body development.
In addition, the human brain becomes very large as it develops, so a woman must give birth to a baby at an early stage of development in order for the infant’s head to fit through her birth canal. Thus, human babies require a long period of care to reach a stage of development at which they depend less on their parents. In contrast with a modern female, a female australopith could give birth to a baby at an advanced stage of development because its brain would not be too large to pass through the birth canal. The need to give birth early, - and therefore to provide more infant care - may have evolved around the time of the middle Homo species Homo ergaster. This species had a brain significantly larger than that of the Australopiths, but a narrow birth canal.
Pair-bonding, usually of a short duration, occurs in a variety of primate species. Some scientists speculate that prolonged bonds developed in humans along with increased sharing of food. Among primates, humans have a distinct type of food-sharing behaviour. People will delay eating food until they have returned with it to the location of other members of their social group. This type of food sharing may have arisen at the same time as the need for intensive infant care, probably by the time of H. ergaster. By devoting himself to a particular female and sharing food with her, a male could increase the chances of survival for his own offspring.
Humans have lived as foragers for millions of years. Foragers obtain food when and where it is available over a broad territory. Modern-day foragers (also known as hunter-gatherers) such as, the San people in the Kalahari Desert of southern Africa who also set up central campsites, or home bases, and divide work duties between men and women. Women gather readily available plant and animal foods, while men take on the often less successful task of hunting. For most of the time since the ancestors of modern humans diverged from the ancestors of the living great apes, around seven million years ago, all humans on Earth f ed themselves exclusively by hunting wild animals and gathered wild planets, as the Blackfeet still did in thee 19th century. It was only within the last 11,000 years that some peoples turned to what is termed food production: that is, domesticating wild animals and planets and eating the resulting livestock and crops. Toda y, most people on Earth consume food that they produced themselves or that someone else produced for them. Some current rates of change, within the next decade the few remaining bands of hunter-gatherers will abandon their ways, disintegrate, or die out, thereby ending our million of the years of commitment to the hunter-gatherers lifestyle. Those few peoples who remained hunter-gatherers into the 20th century escaped replacement by food producers because they ere confined to areas not fit for food production, especially deserts and Arctic regions. Within the present decade, even they will have been seduced by the attractions of civilization, settled down under pressure from bureaucrats or missionaries, or succumbed to germs.
Nevertheless, female and male family members and relatives bring together their food to share at their home base. The modern form of the home base, - that also serves as a haven for raising children and caring for the sick and elderly - may have first developed with middle Homo after about 1.7 million years ago. However, the first evidence of hearths and shelters, - common to all modern home bases - comes from only after 500,000 years ago. Thus, a modern form of social life may not have developed until late in human evolution.
Human subsistence refers to the types of food humans eat, the technology used in and methods of obtaining or producing food, and the ways in which social groups or societies organize themselves for getting, making, and distributing food. For millions of years, humans probably fed on-the-go, much as other primates do. The lifestyle associated with this feeding strategy is generally organized around small, family-based social groups that take advantage of different food sources at different times of year.
The early human diet probably resembled that of closely related primate species. The great apes eat mostly plant foods. Many primates also eat easily obtained animal foods such as insects and bird eggs. Among the few primates that hunt, chimpanzees will prey on monkeys and even small gazelles. The first humans probably also had a diet based mostly on plant foods. In addition, they undoubtedly ate some animal foods and might have done some hunting. Human subsistence began to diverge from that of other primates with the production and use of the first stone tools. With this development, the meat and marrow (the inner, fat-rich tissue of bones) of large mammals became a part of the human diet. Thus, with the advent of stone tools, the diet of early humans became distinguished in an important way from that of apes.
Scientists have found broken and butchered fossil bones of antelopes, zebras, and other comparably sized animals at the oldest archaeological sites, which go on a date from about 2.5 million years ago. With the evolution of late Homo, humans began to hunt even the largest animals on Earth, including mastodons and mammoths, members of the elephant family. Agriculture and the domestication of animals arose only in the recent past, with H. sapiens.
Paleoanthropologists have debated whether early members of the modern human genus were aggressive hunters, peaceful plant gatherers, or opportunistic scavengers. Many scientists once thought that predation and the eating of meat had strong effects on early human evolution. This hunting hypothesis suggested that early humans in Africa survived particularly arid periods by aggressively hunting animals with primitive stone or bone tools. Supporters of this hypothesis thought that hunting and competition with carnivores powerfully influenced the evolution of human social organization and behaviour; toolmaking; anatomy, such as the unique structure of the human hand; and intelligence.
Beginning in the 1960s, studies of apes cast doubt on the hunting hypothesis. Researchers discovered that chimpanzees cooperate in hunts of at least small animals, such as monkeys. Hunting did not, therefore, entirely distinguish early humans from apes, and therefore hunting alone may not have determined the path of early human evolution. Some scientists instead argued in favour of the importance of food-sharing in early human life. According to a food-sharing hypothesis, cooperation and sharing within family groups
- instead of aggressive hunting - strongly influenced the path of human evolution.
Scientists once thought that archaeological sites as much as two million years old provided evidence to support the food-sharing hypothesis. Some of the oldest archaeological sites were places where humans brought food and stone tools together. Scientists thought that these sites represented home bases, with many of the social features of modern hunter-gatherers campsites, including the sharing of food between pair-bonded males and females.
Critique of the food-sharing hypothesis resulted from more careful study of animal bones from the early archaeological sites. Microscopic analysis of these bones revealed the marks of human tools and carnivore teeth, indicating that both humans and potential predators, such as hyenas, cats, and jackals were active at these sites. This evidence suggested that what scientists had thought were home bases where early humans shared food were in fact food-processing sites that humans abandoned to predators. Thus, evidence did not clearly support the idea of food-sharing among early humans.
The new research also suggested a different view of early human subsistence that early humans scavenged meat and bone marrow from dead animals and did little hunting. According to this scavenging hypothesis, early humans opportunistically took parts of animal carcasses left by predators, and then used stone tools to remove marrow from the bones.
Observations that many animals, such as antelope, often die off in the dry season make the scavenging hypothesis quite plausible. Early toolmakers would have had plenty of opportunity to scavenge animal fat and meat during dry times of the year. However, other archaeological studies - and a better appreciation of the importance of hunting among chimpanzees - suggest that the scavenging hypothesis be too narrow. Many scientists now believe that early humans both scavenged and hunted. Evidence of carnivore tooth marks on bones cut by early human toolmakers suggests that the humans scavenged at least the larger of the animals they ate. They also ate a variety of plant foods. Some disagreement remains, however, as to how much early humans relied on hunting, especially the hunting of smaller animals.
Scientists debate when humans first began hunting on a regular basis. For instance, elephant fossils found with tools made by middle Homo once led researchers to the idea that members of this species were hunters of big game. However, the simple association of animal bones and tools at the same site does not necessarily mean that early humans had killed the animals or eaten their meat. Animals may die in many ways, and natural forces can accidentally place fossils next to tools. Recent excavations at Olorgesailie, Kenya, show that H. erectus cut meat from elephant carcasses but give rise of not revealing to whether these humans were regular or specialized hunters.
Humans who lived outside of Africa, - especially in colder temperate climates, - almost necessitated eating more meat than their African counterparts. Humans in temperate Eurasia would have had to learn about which plants they could safely eat, and the number of available plant foods would drop significantly during the winter. Still, although scientists have found very few fossils of edible or eaten plants at early human sites, early inhabitants of Europe and Asia probably did eat plant foods in addition to meat.
Sites that provide the clearest evidence of early hunting include Boxgrove, England, where about 500,000 years ago people trapped a great number of large game animals between a watering hole and the side of a cliff and then slaughtered them. At Schningen, Germany, a site about 400,000 years old, scientists have found wooden spears with sharp ends that were well designed for throwing and probably used in hunting large animals.
Neanderthals and other archaic humans seem to have eaten whatever animals were available at a particular time and place. So, for example, in European Neanderthal sites, the number of bones of reindeer (a cold-weather animal) and red deer (a warm-weather animal) changed depending on what the climate had been like. Neanderthals probably also combined hunting and scavenging to obtain animal protein and fat.
For at least the past 100,000 years, various human groups have eaten foods from the ocean or coast, such as shellfish and some sea mammals and birds. Others began fishing in interior rivers and lakes. Between probably 90,000 and 80,000 years ago people in Katanda, in what is now the Democratic Republic of the Congo, caught large catfish using a set of barbed bone points, the oldest known specialized fishing implements. The oldest stone tips for arrows or spears date from about 50,000 to 40,000 years ago. These technological advances, probably first developed by early modern humans, indicate an expansion in the kinds of foods humans could obtain.
Beginning 40,000 years ago humans began making even more significant advances in hunting dangerous animals and large herds, and in exploiting ocean resources. People cooperated in large hunting expeditions in which they killed great numbers of reindeer, bison, horses, and other animals of the expansive grasslands that existed at that time. In some regions, people became specialists in hunting certain kinds of animals. The familiarity these people had with the animals they hunted appears in sketches and paintings on cave walls, dating from as much as 32,000 years ago. Hunters also used the bones, ivory, and antlers of their prey to create art and beautiful tools. In some areas, such as the central plains of North America that once teemed with a now-extinct type of large bison (Bison occidentalis), hunting may have contributed to the extinction of entire species.
The making and use of tools alone probably did not distinguish early humans from their ape predecessors. Instead, humans made the important breakthrough of using one tool to make another. Specifically, they developed the technique of precisely hitting one stone against another, known as knapping. Stone toolmaking characterized the period sometimes referred to as the Stone Age, which began at least 2.5 million years ago in Africa and lasted until the development of metal tools within the last 7,000 years (at different times in different parts of the world). Although early humans may have made stone tools before 2.5 million years ago, toolmakers may not have remained long enough in one spot to leave clusters of tools that an archaeologist would notice today.
The earliest simple form of stone toolmaking involved breaking and shaping an angular rock by hitting it with a palm-sized round rock known as a hammerstone. Scientists refer to tools made in this way as Oldowan, after Olduvai Gorge in Tanzania, a site from which many such tools have come. The Oldowan tradition lasted for about one million years. Oldowan tools include large stones with a chopping edge, and small, sharp flakes that could be used to scrape and slice. Sometimes Oldowan toolmakers used anvil stones (flat rocks found or placed on the ground) on which hard fruits or nuts could be broken open. Chimpanzees are known to do this today.
Scientists once thought that Oldowan toolmakers intentionally produced several different types of tools. It now appears that differences in the shapes of larger tools were some byproducts of detaching flakes from a variety of natural rock shapes. Learning the skill of Oldowan toolmaking assiduously required observation, but not necessarily instruction or language. Thus, Oldowan tools were simple, and their makers used them for such purposes as cutting up animal carcasses, breaking bones to obtain marrow, cleaning hides, and sharpening sticks for digging up edible roots and tubers.
Oldowan toolmakers sought out the best stones for making tools and carried them to food-processing sites. At these sites, the toolmakers would butcher carcasses and eat the meat and marrow, thus avoiding any predators that might return to a kill. This behaviour of bringing food and tools together contrasts with an eat-as-you-go strategy of feeding commonly seen in other primates.
The Acheulean toolmaking traditions, which began sometime between 1.7 million and 1.5 million years ago, consisted of increasingly symmetrical tools, most of which scientists refer to as hand-axes and cleavers. Acheulean toolmakers, such as Homo erectus, also worked with much larger pieces of stone than did Oldowan toolmakers. The symmetry and size of later Acheulean tools show increased planning and design - and thus probably increased intelligence - on the part of the toolmakers. The Acheulean tradition continued for more than 1.35 million years.
The next significant advances in stone toolmaking were made by at least 200,000 years ago. One of these methods of toolmaking, known as the prepared core technique (and Levallois in Europe), involved carefully and exactingly knocking off small flakes around one surface of a stone and then striking it from the side to produce a preformed tool blank, which could then be worked further. Within the past 40,000 years, modern humans developed the most advanced stone toolmaking techniques. The so-called prismatic-blade core toolmaking technique involved removing the top from a stone, leaving a flat platform, and then breaking off multiple blades down the sides of the stone. Each blade had a triangular cross-section, giving it excellent strength. Using these blades as blanks, people made exquisitely shaped spearheads, knives, and numerous other kinds of tools. The most advanced stone tools also exhibit distinct and consistent regional differences in style, indicating a high degree of cultural diversity.
Early humans experienced dramatic shifts in their environments over time. Fossilized plant pollen and animal bones, along with the chemistry of soils and sediments, reveal much about the environmental conditions to which humans had to adapt.
By eight million years ago, the continents of the world, which move over very long periods, had come to the positions they now occupy. However, the crust of the Earth has continued to move since that time. These movements have dramatically altered landscapes around the world. Important geological changes that affected the course of human evolution include those in southern Asia that formed the Himalayan mountain chain and the Tibetan Plateau, and those in eastern Africa that formed the Great Rift Valley. The formation of major mountain ranges and valleys led to changes in wind and rainfall patterns. In many areas dry seasons became more pronounced, and in Africa conditions became generally cooler and drier.
By five million years ago, the amount of fluctuation in global climate had increased. Temperature fluctuations became quite pronounced during the Pliocene Epoch (five million to 1.6 million years ago). During this time the world entered a period of intense cooling called an ice age, which began from place to place of 2.8 million years ago. Ice ages cycle through colder phases known as glacial (times when glaciers form) and warmer phases known as interglacial (during which glaciers melt). During the Pliocene, glacial and interglacial each lasted about 40,000 years each. The Pleistocene Epoch (1.6 million to 10,000 years ago), in contrast, had much larger and longer ice age fluctuations. For instance, beginning about 700,000 years ago, these fluctuations repeated roughly every 100,000 years.
Between five million and two million years ago, a mixture of forests, woodlands, and grassy habitats covered most of Africa. Eastern Africa entered a significant drying period around 1.7 million years ago, and after one million years ago large parts of the African landscape turned to grassland. So the early Australopiths and early Homo lived in relatively wooded places, whereas Homo ergaster and H. erectus lived in areas of Africa that were more open. Early human populations encountered many new and different environments when they spread beyond Africa, including colder temperatures in the Near East and bamboo forests in Southeast Asia. By about 1.4 million years ago, populations had moved into the temperate zone of northeast Asia, and by 800,000 years ago they had dispersed into the temperate latitudes of Europe. Although these first excursions to latitudes of 400 north and higher may have occurred during warm climate phases, these populations also must have encountered long seasons of cold weather.
All of these changes, - dramatic shifts in the landscape, changing rainfall and drying patterns, and temperature fluctuations posed challenges to the immediate and long-term survival of early human populations. Populations in different environments evolved different adaptations, which in part explains why more than one species existed at the same time during much of human evolution.
Some early human adaptations to new climates involved changes in physical (anatomical) form. For example, the physical adaptation of having a tall, lean body such as that of H. ergaster, - with lots of skin exposed to cooling winds - would have dissipated heat very well. This adaptation probably helped the species to survive in the hotter, more open environments of Africa around 1.7 million years ago. Conversely, the short, wide bodies of the Neanderthals would have conserved heat, helping them to survive in the ice age climates of Europe and western Asia
Increases in the size and complexity of the brain, however, made early humans progressively better at adapting through changes in cultural behaviour. The largest of these brain-size increases occurred over the past 700,000 years, a period during which global climates and environments fluctuated dramatically. Human cultural behaviour also evolved more quickly during this period, most likely in response to the challenges of coping with unpredictable and changeable surroundings
Humans have always adapted to their environments by adjusting their behaviour. For instance, early Australopiths moved both in the trees and on the ground, which probably helped them survive environmental fluctuations between wooded and more open habitats. Early Homo adapted by making stone tools and transporting their food over long distances, thereby increasing the variety and quantities of different foods they could eat. An expanded and flexible diet would have helped these toolmakers survive unexpected changes in their environment and food supply
When populations of H. erectus moved into the temperate regions of Eurasia, but they faced new challenges to survival. During the colder seasons they had to either move away or seek shelter, such as in caves. Some of the earliest definitive evidence of cave dwellers dates from around 800,000 years ago at the site of Atapuerca in northern Spain. This site may have been home too early
H. heidelbergensis populations. H. erectus also used caves for shelter.
Eventually, early humans learned to control fire and to use it to create warmth, cook food, and protect themselves from other animals. The oldest known fire hearths date from between 450,000 and 300,000 years ago, at sites such as Bilzingsleben, Germany; Verteszöllös, Hungary; and Zhoukoudian (Chou - k’ou - tien), China. African sites as old as 1.6 million to 1.2 million years contain burned bones and reddened sediments, but many scientists find such evidence too ambiguous to prove that humans controlled fire. Early populations in Europe and Asia may also have worn animal hides for warmth during glacial periods. The oldest known bone needles, which indicate the development of sewing and tailored clothing, date from about 30,000 to 26,000 years ago.
Behaviour relates directly to the development of the human brain, and particularly the cerebral cortex, the part of the brain that allows abstract thought, beliefs, and expression through language. Humans communicate through the use of symbols - ways of referring to things, ideas, and feelings that communicate meaning from one individual to another but that need not have any direct connection to what they identify. For instance, a word - one type of symbol - does not usually relate directly or actualized among the things or indexical to its held idea, but by its representation, it has only of itself for being abstractive.
People can also paint abstract pictures or play pieces of music that evoke emotions or ideas, even though emotions and ideas have no form or sound. In addition, people can conceive of and believe in supernatural beings and powers - abstract concepts that symbolize real-world events such as the creation of Earth and the universe, the weather, and the healing of the sick. Thus, symbolic thought lies at the heart of three hallmarks of modern human culture: language, art, and religion.
In language, people creatively join words together in an endless variety of sentences, - each with a distinct meaning - according to a set of mental rules, or grammar. Language provides the ability to communicate complex concepts. It also allows people to exchange information about both past and future events, about objects that are not present, and about complex philosophical or technical concepts
Language gives people many adaptive advantages, including the ability to plan, to communicate the location of food or dangers to other members of a social group, and to tell stories that unify a group, such as mythologies and histories. However, words, sentences, and languages cannot be preserved like bones or tools, so the evolution of language is one of the most difficult topics to investigate through scientific study.
It appears that modern humans have an inborn instinct for language. Under normal conditions not developing language is almost impossible for a person, and people everywhere go through the same stages of increasing language skill at about the same ages. While people appear to have inborn genetic information for developing language, they learn specific languages based on the cultures from which they come and the experiences they have in life.
The ability of humans to have language depends on the complex structure of the modern brain, which has many interconnected, specific areas dedicated to the development and control of language. The complexity of the brain structures necessary for language suggests that it probably took a long time to evolve. While paleoanthropologists would like to know when these important parts of the brain evolved, endocasts (inside impressions) of early human skulls do not provide enough detail to show this.
Some scientists think that even the early Australopiths had some ability to understand and use symbols. Support for this view comes from studies with chimpanzees. A few chimps and other apes have been taught to use picture symbols or American Sign Language for simple communication. Nevertheless, it appears that language, - as well as art and religious rituals became vital aspects of human life only during the past 100,000 years, primarily within our own species.
Humans also express symbolic thought through many forms of art, including painting, sculpture, and music. The oldest known object of possible symbolic and artistic value dates from about 250,000 years ago and comes from the site of Berekhat Ram, Israel. Scientists have interpreted this object, a figure carved into a small piece of volcanic rock, as a representation of the outline of a female body. Only a few other possible art objects are known from between 200,000 and 50,000 years ago. These items, from western Europe and usually attributed to Neanderthals, include two simple pendants - a tooth and a bone with bored holes, - and several grooved or polished fragments of tooth and bone.
Sites dating from at least 400,000 years ago contain fragments of red and black pigment. Humans might have used these pigments to decorate bodies or perishable items, such as wooden tools or clothing of animal hides, but this evidence would not have survived to today. Solid evidence of the sophisticated use of pigments for symbolic purposes, - such as in religious rituals comes only from after 40,000 years ago. From early in this period, researchers have found carefully made types of crayons used in painting and evidence that humans burned pigments to create a range of colours.
People began to create and use advanced types of symbolic objects between about 50,000 and 30,000 years ago. Much of this art appears to have been used in rituals - possibly ceremonies to ask spirit beings for a successful hunt. The archaeological record shows a tremendous blossoming of art between 30,000 and 15,000 years ago. During this period people adorned themselves with intricate jewellery of ivory, bone, and stone. They carved beautiful figurines representing animals and human forms. Many carvings, sculptures, and paintings depict stylized images of the female body. Some scientists think such female figurines represent fertility.
Early wall paintings made sophisticated use of texture and colour. The area of what is now Southern France contains many famous sites of such paintings. These include the caves of Chauvet, which contain art more than 30,000 years old, and Lascaux, in which paintings date from as much as 18,000 years ago. In some cases, artists painted on walls that can be reached only with special effort, such as by crawling. The act of getting to these paintings gives them a sense of mystery and ritual, as it must have to the people who originally viewed them, and archaeologists refer to some of the most extraordinary painted chambers as sanctuaries. Yet no one knows for sure what meanings these early paintings and engravings had for the people who made them.
Graves from Europe and western Asia indicate that the Neanderthals were the first humans to bury their dead. Some sites contain very shallow graves, which group or family members may have dug simply to remove corpses from sight. In other cases it appears that groups may have observed rituals of grieving for the dead or communicating with spirits. Some researchers have claimed that grave goods, such as meaty animal bones or flowers, had been placed with buried bodies, suggesting that some Neanderthal groups might have believed in an afterlife. In a large proportion of Neanderthal burials, the corpse had its legs and arms drawn in close to its chest, which could indicate a ritual burial position.
Other researchers have challenged these interpretations, however. They suggest that perhaps the Neanderthals had practically rather than religious reasons for positioning dead bodies. For instance, a body manipulated into a fetal position would need only a small hole for burial, making the job of digging a grave easier. In addition, the animal bones and flower pollen near corpses could have been deposited by accident or without religious intention.
Many scientists once thought that fossilized bones of cave bears (a now-extinct species of large bear) found in Neanderthal caves indicated that these people had what has been referred to as a cave bear cult, in which they worshipped the bears as powerful spirits. However, after careful study researchers concluded that the cave bears probably died while hibernating and that Neanderthals did not collect their bones or worship them. Considering current evidence, the case for religion among Neanderthals remains controversial.
One of the most important developments in human cultural behaviour occurred when people began to domesticate (control the breeding of) plants and animals. Domestication and the advent of agriculture led to the development of dozens of staple crops (foods that forms the basis of an entire diet) in temperate and tropical regions around the world. Almost the entire population of the world today depends on just four of these major crops: wheat, rice, corn, and potatoes.
The growth of farming and animal herding initiated one of the most remarkable changes ever in the relationship between humans and the natural environment. The change first began just 10,000 years ago in the Near East and has accelerated very rapidly since then. It also occurred independently in other places, including areas of Mexico, China, and South America. Since the first domestication of plants and animals, many species over large areas of the planet have come under human control. The overall number of plant and animal species has decreased, while the populations of a few species needed to support large human populations have grown immensely. In areas dominated by people, interactions between plants and animals usually fall under the control of a single species, - Homo sapiens.
The rise of civilizations - the large and complex types of societies in which most people still live today - developed along with surplus food production. People of high status eventually used food surpluses as a way to pay for labour and to create alliances among groups, often against other groups. In this way, large villages could grow into city-states (urban centres that governed themselves) and eventually empires covering vast territories. With surplus food production, many people could work exclusively in political, religious, or military positions, or in artistic and various skilled vocations. Command of food surpluses also enabled rulers to control labourers, such as in slavery. All civilizations developed based on such hierarchical divisions of status and vocation.
The earliest civilization arose more than 7,000 years ago in Sumer in what is now Iraq. Sumer grew powerful and prosperous by 5,000 years ago, when it entered on the city-state of Ur. The region containing Sumer, known as Mesopotamia, was the same area in which people had first domesticated animals and plants. Other centres of early civilizations include the Nile Valley of Northeast Africa, the Indus. Valley of South Asia, the Yellow River Valley of East Asia, the Oaxaca and Mexico valleys and the Yucatán region of Central America, and the Andean region of South America, China and Inca Empire.
All early civilizations had some common features. Some of these included a bureaucratic political body, a military, a body of religious leadership, large urban centres, monumental buildings and other works of architecture, networks of trade, and food surpluses created through extensive systems of farming. Many early civilizations also had systems of writing, numbers and mathematics, and astronomy (with calendars); road systems; a formalized body of law; and facilities for education and the punishment of crimes. With the rise of civilizations, human evolution entered a phase vastly different from all before which came. Before this time, humans had lived in small, family-entered groups essentially exposed to and controlled by forces of nature. Several thousand years after the rise of the first civilizations, most people now live in societies of millions of unrelated people, all separated from the natural environment by houses, buildings, automobiles, and numerous other inventions and technologies. Culture will continue to evolve quickly and in unforeseen directions, and these changes will, in turn, influence the physical evolution of Homo sapiens and any other human species to come, - attempt to base ethical reasoning on the presumed fact about evolution. The movement is particularly associated with Spencer, the premise that later elements in an evolutionary path are better than earlier ones, the application of the principle then requires seeing western society, laissez faire capitalism, or another object of approval as more evolved than more ‘primitive’ social forms. Neither the principle nor the application commands much respect. The version of evolutionary ethics called ‘social Darwinism, emphasised the struggle for natural selection, and drew the conclusion that we should glorify and help such struggles, usually by enchaining competitive and aggressive relations between people in society, or between societies themselves. More recently subjective matters and opposing physical theories have rethought the relations between evolution and ethics in the light of biological discoveries concerning altruism and kin-selection.
It is, nevertheless, and, least of mention, that Sociobiology (the academic discipline best known through the work of Edward O. Alison who coined the tern in his Sociobiology: the New Synthesise, 1975). The approach to human behaviour is based on the premise that all social behaviour has a biological basis, and seeks to understand that logical basis as to genetic encoding for features that are themselves selected for through evolutionary history. The philosophical problem is essentially of methodology of finding criteria for identifying features that are objectively manifest in that they can usefully identify features, which classical epistemology can usefully explain in this way, and for finding criteria for assessing various genetic stories that might provide useful explanations among the features proposed for this kind of explanation are such things as male dominance, male promiscuity versus female fidelity, propensities to sympathy and other emotions, and the limited altruism characteristics accused of ignoring the influence of environmental and social factors in moulding people’s characteristics, e.g., at the limit of silliness, by postulating a ‘gene for poverty, however there is no need for the approach to commit such errors, since the feature explained sociobiologically may be indexical to environmental considerations: For instance, it may be a propensity to develop some feature in some social or order environment (or even a propensity to develop propensities . . . ). That man’s problem was to separate genuine explanation from speculatively methodological morally stories, which may or may not identify really selective mechanisms
Scientists are unbiased observers who use the scientific method to confirm conclusively and falsify various theories. These experts have no preconceptions in gathering the data and logically derive theories from these objective observations. One great strength of science is that its self-correcting, because scientists readily abandon theories when their use has been forfeited, and then again they have shown them to be irrational, although many people have accepted such eminent views of science, they are almost completely untrue. Data can neither conclusively confirm nor conclusively falsify theories, there really is no such thing as the scientific method, data become subjective in practice, and scientists have displayed a surprising fierce loyalty to their theories. There have been many misconceptions of what science is and what science is not.
Science, is, and should be the systematic study of anything that breathes, walk in its own motion of a bipedal erection, and have some regarding its own Beingness, and, of course, have its to some form of living fashion. In that others of science can examine, test, and verify. Not-knowing or knowing has derived the word science from the Latin word scribe meaning ‘to know.’ From its beginnings, science has developed into one of the greatest and most influential fields of human endeavour. Today different branches of science investigate almost everything that thumps in the night in that can observe or detect, and science as the whole shape in the way we understand the universe, our planet, ourselves, and other living things.
Science develops through objective analysis, instead of through personal belief. Knowledge gained in science accumulates as time goes by, building on work performed earlier. Some of this knowledge, such as our understanding of numbers, stretches back to the time of ancient civilizations, when scientific thought first began. Other scientific knowledge, - such as our understanding of genes that cause cancer or of quarks (the smallest known building block of matter), dates back to less than 50 years. However, in all fields of science, old or new, researchers use the same systematic approach, known as the scientific method, to add to what governing evolutionary principles have known.
During scientific investigations, scientists put together and compare new discoveries and existing knowledge. Commonly, new discoveries extend what continuing phenomenons have currently accepted, providing further evidence that existing idea are correct. For example, in 1676 the English physicist Robert Hooke discovered those elastic objects, such as metal springs, stretches in proportion to the force that acts on them. Despite all the advances made in physics since 1676, this simple law still holds true.
Scientists use existing knowledge in new scientific investigations to predict how things will behave. For example, a scientist who knows the exact dimensions of a lens can predict how the lens will focus a beam of light. In the same way, by knowing the exact makeup and properties of two chemicals, a researcher can predict what will happen when they combine. Sometimes scientific predictions go much further by describing objects or events those existing object relations have not yet known. An outstanding instance occurred in 1869, when the Russian chemist Dmitry Mendeleyev drew up a periodic table of the elements arranged to illustrate patterns of recurring chemical and physical properties. Mendeleyev used this table to predict the existence and describe the properties of several elements unknown in his day, and when the mysteriousness of science began the possibilities of experimental simplicities in the discovering enactments whose elements, under which for the several years past, the later, predictions were correct.
In science, and only through experimentation can we find the sublime simplicities of our inherent world, however, by this similarity to theoretical implications can we manifest of what can also be made important as when current ideas are shown to be wrong. A classic case of this occurred early in the 20th century, when the German geologist Alfred Wegener suggested that the continents were at once connected, a theory known as continental drift. At the time, most geologists discounted Wegener's ideas, because the Earth's crust may be fixed. However, following the discovery of plate tectonics in the 1960's, in which scientists found that the Earth’s crust is made of moving plates, continental drift became an important part of geology.
Through advances like these, scientific knowledge is constantly added to and refined. As a result, science gives us an ever more detailed insight into the way the world around us works.
For a large part of recorded history, science had little bearing on people's everyday lives. Scientific knowledge was gathered for its own sake, and it had few practical applications. However, with the dawn of the Industrial Revolution in the 18th century, this rapidly changed. Today, science affects the way we live, largely through technology - the use of scientific knowledge for practical purposes.
Some forms of technology have become so well established that forgetting the great scientific achievements that they represent is easy. The refrigerator, for example, owes its existence to a discovery that liquids take in energy when they evaporate, a phenomenon known as latent heat. The principle of latent heat was first exploited in a practical way in 1876, and the refrigerator has played a major role in maintaining public health ever since. The first automobile, dating from the 1880's, used many advances in physics and engineering, including reliable ways of generating high-voltage sparks, while the first computers emerged in the 1940's from simultaneous advances in electronics and mathematics.
Other fields of science also play an important role in the things we use or consume every day. Research in food technology has created new ways of preserving and flavouring what we eat. Research in industrial chemistry has created a vast range of plastics and other synthetic materials, which have thousands of uses in the home and in industry. Synthetic materials are easily formed into complex shapes and can be used to make machine, electrical, and automotive parts, scientific and industrial instruments, decorative objects, containers, and many other items. Alongside these achievements, science has also caused technology that helps save human life. The kidney dialysis machine enables many people to survive kidney diseases that would once have proved fatal, and artificial valves allow sufferers of coronary heart disease to return to active living. Biochemical research is responsible for the antibiotics and vaccinations that protect us from infectious diseases, and for a wide range of other drugs used to combat specific health problems. As a result, the majority of people on the planet now live longer and healthier lives than ever before.
However, scientific discoveries can also have a negative impact in human affairs. Over the last hundred years, some technological advances that make life easier or more enjoyable have proved to have unwanted and often unexpected long-term effects. Industrial and agricultural chemicals pollute the global environment, even in places as remote as Antarctica, and city air is contaminated by toxic gases from vehicle exhausts. The increasing pace of innovation means that products become rapidly obsolete, adding to a rising tide of waste. Most significantly of all, the burning of fossil fuels such as coal, oil, and natural gas releases into the atmosphere carbon dioxide and other substances knew as greenhouse gases. These gases have altered the composition of the entire atmosphere, producing global warming and the prospect of major climate change in years to come.
Science has also been used to develop technology that raises complex ethical questions. This is particularly true in the fields of biology and medicine. Research involving genetic engineering, cloning, and in vitro fertilization gives scientists the unprecedented power to cause new life, or to devise new forms of living things. At the other extreme, science can also generate technology that is deliberately designed to harm or to kill. The fruits of this research include chemical and biological warfare, and nuclear weapons, by far the most destructive weapons that the world has ever known.
Scientific research can be divided into basic science, also known as pure science, and applied science. In basic science, scientists working primarily at academic institutions pursue research simply to satisfy the thirst for knowledge. In applied science, scientists at industrial corporations conduct research to achieve some kind of practical or profitable gain.
In practice, the division between basic and applied science is not always clear-cut. This is because discoveries that initially seem to have no practical use often develop one as time goes away. For example, superconductivity, the ability to conduct electricity with no resistance, was little more than a laboratory curiosity when Dutch physicist Heike Kamerlingh Onnes discovered it in 1911. Today superconducting electromagnets are used in several of important applications, from diagnostic medical equipment to powerful particle accelerators.
Scientists study the origin of the solar system by analysing meteorites and collecting data from satellites and space probes. They search for the secrets of life processes by observing the activity of individual molecules in living cells. They observe the patterns of human relationships in the customs of aboriginal tribes. In each of these varied investigations the questions asked and the means employed to find answers are different. All the inquiries, however, share a common approach to problem solving known as the scientific method. Scientists may work alone or they may collaborate with other scientists. Always, a scientist’s work must measure up to the standards of the scientific community. Scientists submit their findings to science forums, such as science journals and conferences, to subject the findings to the scrutiny of their peers.
Whatever the aim of their work, scientists use the same underlying steps to organize their research: (1) they make detailed observations about objects or processes, either as they occur in nature or as they take place during experiments; (2) they collect and analyse the information observed; and (3) they formulate a hypothesis that explains the behaviour of the phenomena observed.
A scientist begins an investigation by observing an object or an activity. Observations typically involve one or more of the human senses, like hearing, sight, smells, tastes, and touch. Scientists typically use tools to aid in their observations. For example, a microscope helps view objects too small to be seen with the unaided human eye, while a telescope views objects too far away to be seen by the unaided eye.
Scientists typically implement their observation skills to an experiment. An experiment is any kind of trial that enables scientists to control and change at will the conditions under which events occur. It can be something extremely simple, such as heating a solid to see when it melts, or the periodical perception to differences of complexity, such as bouncing a radio signal off the surface of a distant planet. Scientists typically repeat experiments, sometimes many times, in order to be sure that the results were not affected by unforeseen factors.
Most experiments involve real objects in the physical world, such as electric circuits, chemical compounds, or living organisms. However, with the rapid progress in electronics, computer simulations can now carry out some experiments instead. If they are carefully constructed, these simulations or models can accurately predict how real objects will behave.
One advantage of a simulation is that it allows experiments to be conducted without any risks. Another is that it can alter the apparent passage of time, speeding up or slowing natural processes. This enables scientists to investigate things that happen very gradually, such as evolution in simple organisms, or ones that happen almost instantaneously, such as collisions or explosions.
During an experiment, scientists typically make measurements and collect results as they work. This information, known as data, can take many forms. Data may be a set of numbers, such as daily measurements of the temperature in a particular location or a description of side effects in an animal that has been given an experimental drug. Scientists typically use computers to arrange data in ways that make the information easier to understand and analysed data may be arranged into a diagram such as a graph that shows how one quantity (body temperature, for instance) varies in relation to another quantity (days since starting a drug treatment). A scientist flying in a helicopter may collect information about the location of a migrating herd of elephants in Africa during different seasons of a year. The data collected maybe in the form of geographic coordinates that can be plotted on a map to provide the position of the elephant herd at any given time during a year.
Scientists use mathematics to analyse the data and help them interpret their results. The types of mathematical use that include statistics, which is the analysis of numerical data, and probability, which calculates the likelihood that any particular event will occur.
Once an experiment has been carried out, data collected and analysed, scientists look for whatever pattern their results produce and try to formulate a hypothesis that explains all the facts observed in an experiment. In developing a hypothesis, scientists employ methods of induction to generalize from the experiment’s results to predict future outcomes, and deduction to infer new facts from experimental results.
Formulating a hypothesis may be difficult for scientists because there may not be enough information provided by a single experiment, or the experiment’s conclusion may not fit old theories. Sometimes scientists do not have any prior idea of a hypothesis before they start their investigations, but often scientists start out with a working hypothesis that will be proved or disproved by the results of the experiment. Scientific hypotheses can be useful, just as hunches and intuition can be useful in everyday life. Still, they can also be problematic because they tempt scientists, either deliberately or unconsciously, to favour data that support their ideas. Scientists generally take great care to avoid bias, but it remains an ever-present threat. Throughout the history of science, numerous researchers have fallen into this trap, either in the promise of self-advancement that perceive to be the same or that they firmly believe their ideas to be true.
If a hypothesis is borne out by repeated experiments, it becomes a theory - an explanation that seems to fit with the facts consistently. The ability to predict new facts or events is a key test of a scientific theory. In the 17th century German astronomer Johannes Kepler proposed three theories concerning the motions of planets. Kepler’s theories of planetary orbits were confirmed when they were used to predict the future paths of the planets. On the other hand, when theories fail to provide suitable predictions, these failures may suggest new experiments and new explanations that may lead to new discoveries. For instance, in 1928 British microbiologist Frederick Griffith discovered that the genes of dead virulent bacteria could transform harmless bacteria into virulent ones. The prevailing theory at the time was that genes were made of proteins. Nevertheless, studies performed by Canadian-born American bacteriologist Oswald Avery and colleagues in the 1930's repeatedly showed that the transforming gene was active even in bacteria from which protein was removed. The failure to prove that genes were composed of proteins spurred Avery to construct different experiments and by 1944 Avery and his colleagues had found that genes were composed of deoxyribonucleic acid (DNA), not proteins.
If other scientists do not have access to scientific results, the research may as well not have been performed at all. Scientists need to share the results and conclusions of their work so that other scientists can debate the implications of the work and use it to spur new research. Scientists communicate their results with other scientists by publishing them in science journals and by networking with other scientists to discuss findings and debate issues.
In science, publication follows a formal procedure that has set rules of its own. Scientists describe research in a scientific paper, which explains the methods used, the data collected, and the conclusions that can be drawn. In theory, the paper should be detailed enough to enable any other scientist to repeat the research so that the findings can be independently checked.
Scientific papers usually begin with a brief summary, or abstract, that describes the findings that follow. Abstracts enable scientists to consult papers quickly, without having to read them in full. At the end of most papers is a list of citations - bibliographic references that acknowledge earlier work that has been drawn on in the course of the research. Citations enable readers to work backwards through a chain of research advancements to verify that each step is
soundly based.
Scientists typically submit their papers to the editorial board of a journal specializing in a particular field of research. Before the paper is accepted for publication, the editorial board sends it out for peer review. During this procedure a panel of experts, or referees, assesses the paper, judging whether or not the research has been carried out in a fully scientific manner. If the referees are satisfied, publication goes ahead. If they have reservations, some of the research may have to be repeated, but if they identify serious flaws, the entire paper may be rejected from publication.
The peer-review process plays a critical role because it ensures high standards of scientific method. However, it can be a contentious area, as it allows subjective views to become involved. Because scientists are human, they cannot avoid developing personal opinions about the value of each other’s work. Furthermore, because referees tend to be senior figures, they may be less than welcoming to new or unorthodox ideas.
Once a paper has been accepted and published, it becomes part of the vast and ever-expanding body of scientific knowledge. In the early days of science, new research was always published in printed form, but today scientific information spreads by many different means. Most major journals are now available via the Internet (a network of linked computers), which makes them quickly accessible to scientists all over the world.
When new research is published, it often acts as a springboard for further work. Its impact can then be gauged by seeing how often the published research appears as a cited work. Major scientific breakthroughs are cited thousands of times a year, but at the other extreme, obscure pieces of research may be cited rarely or not at all. However, citation is not always a reliable guide to the value of scientific work. Sometimes a piece of research will go largely unnoticed, only to be rediscovered in subsequent years. Such was the case for the work on genes done by American geneticist Barbara McClintock during the 1940s. McClintock discovered a new phenomenon in corn cells known as ‘transposable genes’, sometimes referred to as jumping genes. McClintock observed that a gene could move from one chromosome to another, where it would break the second chromosome at a particular site, insert itself there, and influence the function of an adjacent gene. Her work was largely ignored until the 1960s when scientists found that transposable genes were a primary means for transferring genetic material in bacteria and more complex organisms. McClintock was awarded the 1983 Nobel Prize in physiology or medicine for her work in transposable genes, more than 35 years after doing the research.
In addition to publications, scientists form associations with other scientists from particular fields. Many scientific organizations arrange conferences that bring together scientists to share new ideas. At these conferences, scientists present research papers and discuss their implications. In addition, science organizations promote the work of their members by publishing newsletters and Web sites; networking with journalists at newspapers, magazines, and television stations to help them understand new findings; and lobbying lawmakers to promote government funding for research.
The oldest surviving science organization is the Academia dei Lincei, in Italy, which was established in 1603. The same century also saw the inauguration of the Royal Society of London, founded in 1662, and the Académie des Sciences de Paris, founded in 1666. American scientific societies date back to the 18th century, when American scientist and diplomat Benjamin Franklin founded a philosophical club in 1727. In 1743 this organization became the American Philosophical Society, which still exists today.
In the United States, the American Association for the Advancement of Science (AAAS) plays a key role in fostering the public understanding of science and in promoting scientific research. Founded in 1848, it has nearly 300 affiliated organizations, many of which originally developed from AAAS special-interest groups.
Since the late 19th century, communication among scientists has also been improved by international organizations, such as the International Bureau of Weights and Measures, founded in 1873, the International Council of Research, founded in 1919, and the World Health Organization, founded in 1948. Other organizations act as international forums for research in particular fields. For example, the Intergovernmental Panel on Climate Change (IPCC), established in 1988, assesses research on how climate change occurs, and what affects change is likely to have on humans and their environment.
Classifying sciences involves arbitrary decisions because the universe is not easily split into separate compartments. This article divides science into five major branches: mathematics, physical sciences, earth sciences, life sciences, and social sciences. A sixth branch, technology, draws on discoveries from all areas of science and puts them to practical use. Each of these branches itself consists of numerous subdivisions. Many of these subdivisions, such as astrophysics or biotechnology, combine overlapping disciplines, creating yet more areas of research.
The mathematical sciences investigate the relationships between things that can be measured or quantified in either a real or abstract form. Pure mathematics differs from other sciences because it deals solely with logic, rather than with nature's underlying laws. However, because it can be used to solve so many scientific problems, mathematics is usually considered to be a science itself.
Central to mathematics is arithmetic, the use of numbers for calculation. In arithmetic, mathematicians combine specific numbers to produce a result. A separate branch of mathematics, called algebra, works in a similar way, but uses general expressions that apply to numbers as a whole. For example, if there are three separate items on a restaurant bill, simple arithmetic produces the total amount to be paid. Nevertheless, the total can also be calculated by using an algebraic formula. A powerful and flexible tool, algebra enables mathematicians to solve highly complex problems in every branch, and, least of mention, geometry too investigates objects and the spaces around them. In its simplest form, it deals with objects in two or three dimensions, such as lines, circles, cubes, and spheres. Geometry can be extended to cover abstractions, including objects in many dimensions.
Analytic geometry arose from the recognition that certain numerical Analytic geometry and algebraic equations correspond to points, lines, and geometric figures. Graphing the equations using a set of axes and co-ordinates drawn to the points, lines, or figures. For example, any point in a plane can be located with respect to a pair of perpendicular axes by specifying the distance of the point from each of these axes. Positive x numbers are located at the right side of the y-axis and negative numbers to the left; positive y numbers are located above the x-axis and negative y numbers below.
Point E is one unit from the vertical y-axis and four units from the horizontal x-axis. The coordinates of point e are therefore one and four, and the point is located by the equations x = 1, y = 4. Similarly, a straight line always corresponds to an equation of the form x + by + c = 0. For example, the collection of points that lie on the straight line passing through points E and F satisfies the equation x + y = 5 (in this simple equation, a and b are both equal to one and c is equal to zero). Every combination of x and y values that satisfy the equation locates a point on the line. Other more complex equations correspond to circles, ellipses, conic sections, and other figures.
The problems dealt within analytic geometry are of two classic kinds. The first kind of problem: Given a geometric description of a set of points, determine the algebraic equation that is satisfied by these points. The second kind of problem: Given an algebraic statement, describe the locations of the points that satisfy the statement in geometric terms. For example, a circle of radius three with its centre at the point of intersection of the x-axis and the y-axis (the origin) is the collection of points that satisfy the equation x2 + y2 = 9. From such equations as these solving geometrical construction problems are possible such as bisecting (dividing exactly in half) a given line segment or angle, constructing a perpendicular to a given line at a given point, or drawing a circle that will pass through three given points that are not on the same straight line.
Points, lines, and figures in three-dimensional space can be similarly located with respect to three axes, of which the third, usually called the z-axis, is perpendicular to the other two at their point of intersection, which is also called the origin.
Analytic geometry was of great value in the development of mathematics because it unified the concepts of analysis (number relationships) and geometry (space relationships). The techniques of analytic geometry, which made possible the representation of numbers and of algebraic expressions in geometric terms, have cast new light on calculus, the theory of functions, and other problems in higher mathematics. The study of non-Euclidean geometry and the geometries of spaces that have more than three dimensions would not have been possible without the analytic approach.
It is often thought that the discovery of non-Euclidean geometries has discredited Kant (1936) and some Kantians have maintained with equal fervour
that nothing of the sort has occurred because what Kant really said, properly interpreted, is quite consistent with there being non-Euclidean geometries (Martin (1951), Nelson (1906), Meinecke (1906), Natorp (I92I), Becker (1927)) . . . indeed Kant himself envisaged this possibility.
The issue is obscured by the fact that the word `space' can be used in four different ways. It can be used, first, as a term of pure mathematics, as when mathematicians talk of a `n-dimensional phase-space', a `n-dimensional vector-space', a `three-dimensional projective space' or a `two-dimensional Riemannian space'. In this sense the word `space' means the totality of the abstract entities-the `points'-implicitly defined by the axioms. There is no doubt that there exist, iii this sense, non-Euclidean spaces, because all that is claimed by such an assertion is that sets of non-Euclidean axioms constitute possible implicit definitions of abstract entities, that is to say that some sets of non-Euclidean axioms are consistent. If Kant or any other philosopher had denied this, he would have been wrong; although Kant himself took care not to deny it, 2 and there is little reason to suppose that any philosopher concerned about space has been using the word in this, the pure mathematician's, sense.
The second use of the word is that of the physicist. The word `line', for example, may be taken to be exemplified by the path of a light-ray, or the path of a freely moving particle, or a geodesic (the shortest distance between two points). Under such interpretation, the axioms or some of the theorems will state synthetic propositions that can be put to an empirical test. It then becomes an empirical question whether a particular set of geometrical axioms under a particular interpretation is true or not; and, as is fairly well known, if we interpret straight lines for being the paths of light rays, space turns out to be not Euclidean but Riemannian.
The concept of geometry. It is only under a given interpretation that a set of axioms becomes physically determinate, and capable of being tested and found to be true or false. A physicist can always avoid having to reject a set of axioms as false by refusing the interpretation under which they turn out to be false. There may be another interpretation, equally acceptable, under which the axioms turn out to be true. Whether an interpretation is acceptable or not is more a matter for the physicists' judgement than a question to be decided definitely by empirical test. Overall, it is possible to secure an interpretation under which a certain set of axioms-say the Euclidean axioms-will come out true, but this interpretation may be purchased at the price of having to have a more complicated physical theory than otherwise. If I interpret straight line as `path of freely moving particle' and then posit various gravitational and other forces to bring it about that a great many apparently free moving particles are not really moving freely, then I will not be able to maintain that space is really Euclidean, but that physics is a good deal more complicated than Einstein made out. Poincaré (I902, 1905) was prepared to pay such a price. He thought that non-Euclidean Geometries were so inconvenient, and that it was so important to have the geometry on which physics is based Euclidean, that he was prepared to forgo all the simplicity and elegance of the General Theory of Relativity in order too secure for physics a fundamental Euclidean basis.
Poincaré's belief in the fundamental preeminence of Euclidean Geometry is a view that is often, and with some show of justice, taken to be the natural modern analogue of Kant's. This is a third sense of the word `space', in which it is claimed that it is a necessary condition, perhaps a subjective condition depending on the nature of the human mind, that the space we actually think of should be a Euclidean space. Space in this sense is neither the pure mathematician's construct nor the remote object of the sophisticated physicist's discovery, but the space of our ordinary experience, given to us, and given to us under a standard interpretation, in all our visual and tactile experience. Some connection is claimed between some central aspects of experience and the Euclidean nature of the space in which this experience is given us that makes it unthinkable that space in this third sense should not be Euclidean.
It seems to me that Kant did maintain that space in this third sense was necessarily Euclidean. However, the issue is clouded by the fact that often when he talks of space, he is using the word not in this but in a fourth sense, a sense in which it makes no sense to ask whether space is Euclidean or not. `In the beginning', Newton rewrote Genesis 1:1, `God created atoms and the void.' The void is that in which atoms may or may not occupy a place, and moving through which may occupy different places at different times. Newton's concept of atoms and the void was an idealisation of our ordinary concept of things, each one occupying at a given time a certain place. The concept of space in this fourth sense provides room for things to exist in. Every point in space is a possibility of existence, in the sense that a thing may, or may not, exist at that point at a given moment; may, or may not, occupy that position. More fundamentally we may argue that some concept of space is a necessary condition, first of our being able to say that two things are qualitatively identical but numerically distinct, and secondly of our being able to say that a thing has changed while remaining the same thing. It is not our task here to unravel the various arguments that Kant and other philosophers have used in order to demonstrate that Space is a necessary concomitant of the other fundamental categories of Time, Substance, Change or Motion. All we need to point out is that the Space that these arguments are concerned with is more primitive than the space about which it can be asked whether it is Euclidean or not. Space in this fourth sense needs to have certain topological properties-continuity, connectedness etc.-but not any metrical properties, and therefore cannot be inconsistent with there being spaces, in another sense, that are non-Euclidean. It is because Kant was chiefly concerned with space in this fourth sense that commentators have claimed that the discovery of non-Euclidean geometries has not in the least discredited his views.
Nevertheless, some unease remains; Kant did sometimes use space in the third sense, and the discovery of non-Euclidean geometries does therefore seem to discredit the view that space in this sense must necessarily be Euclidean. It is this view that to rehabilitate whereas not in Kant's terms will undoubtingly attempt to vindicate the special status of Euclidean geometry and show why it holds a pre-eminent place in our affections.
Euclid was perhaps unfortunate in that his genius led him to hit upon the parallel postulate as his fundamental axiom and not some equivalent proposition. It was natural enough when geometry was concerned with laying out the boundaries of fields along the Nile to regard parallel boundaries as particularly important. But other concepts are equally adequate and even more important. John Wallis, one of the first mathematicians in modern times to consider Euclid's fifth postulate, showed that it could be replaced by an axiom saying that, given a figure, another figure is possible which is similar to the given one and of any size whatsoever; and Gerolamo Saccheri (I733) pointed out that it is enough simply to postulate that there exist two unequal triangles with equal angles.
We thus see that it is a necessary condition of our being able to apply the concept `same shape though different size' that our geometry should be Euclidean. We might almost say that it was a condition of our having the concept of shape at all-for in a Projective Geometry, which contains no concept of size, similarity of geometrical configuration would be of too general application to be a reasonable analogue of our concept of shape; while in Elliptic and Hyperbolic Geometry, although there is a concept of size as well as one analogous to our concept of shape, since the two cannot vary independently, it would be unlikely, or at least difficult, for the two to be distinguished in the way we distinguish them. Euclidean Geometry, if not an absolutely necessary condition for the existence of the concept of shape, is the only ecological environment in which that concept can flourish and prosper. Thus the price of abandoning Euclidean Geometry would be the loss of an important respect in which things can be similar to or dissimilar from one another. We should still have course be able to classify things by colour, by chemical composition, by weight or by specific heat: but we should no longer be able to classify by shape, and this would be awkward; not only would our concepts of area and volume become cumbersome if squares and cubes could not be fitted together to form larger squares or cubes or subdivided into smaller constituent squares or cubes, but it would be conceptually impossible to have scale models, diagrams, maps or blueprints; which would be a pity?
Euclid, verifies' the congruence of two triangles having two sides and the included angle equal by the method of superimposition; supposing triangle ABC be superimposed on to (epharmozenou epi ton) triangle DEF. He has been much criticised for this: superimposition, it is said, is not a proper geometrical method; we cannot properly derive proposition I.4 from the axioms by this method-indeed, we cannot properly derive it at all, and proposition 1.4 should not be stated as a theorem but as an axiom. In modern systems it is given as one of the axioms of congruence. The method Of 1.4 although outside the canon of geometrical methods, has some intuitive appeal, and does in truth reveal an alternative approach to geometry, an approach in which we consider what things we can do to geometrical figures without destroying their geometrical properties superimpose, move, turn, turn over, add more lines to, construct circles round. This "operational" method was extruded from the canon of geometrical propriety by Plato, who thought it ridiculous to talk of doing things (pattern)in geometry not so much because of his discovery of the axiomatic method as a consequence of his allegiance to the theory of forms. Knowledge could only be of what was unchanging (tou aei ontos). Aristotle, rejecting the metaphysics that made it plausible, retained the view that geometry must be entirely static; `mathematics is a theoretical science concerned with things that are stationary (Manunda) but not separable, and mathematicians have had a bad conscience ever since about the operational metaphors they have continually found themselves using. It is only in the last century that a theory of operators has been developed. Felix Klein suggested in his Erlanger Program that it would be fruitful to consider for each geometry what groups of operators would leave the geometrical properties of figures unchanged. Helmholtz was on the track of the same idea, which was tidied up mathematically by Lie (1890) and now offers an alternative approach to geometry, quite as rigorous as the traditional axiomatic approach and entirely respectable, in which we consider various groups of operators operating upon the members of a given set.
Euclidean Geometry then emerges as the geometry in which the three operators of displacement, rotation, and reflection are possible without alteration of geometrical properties. These operations can be defined algebraically as transformations of the general form: xi = Sigma yijxj+ai: Where the matrix (Yi) is an `orthogonal' matrix, that is, has its inverse equal to its transpose (and therefore its determinant equal to ± 1). In effect, this transformation rotates, or turns, a figure through an angle (the effect of the orthogonal matrix), possibly reflects it into its mirror image (if the determinant is equal to -1), and translates, or displaces, it is distanced by direction i.
This algebraic transformation appeals to the algebraist for being the simplest and most fundamental transformation with which he can deal. We can also see, independently of algebra, that the three operations involved are pre-eminently important. Reflection (given any axis of reflection) is essentially a discrete operation: rotation and displacement are continuous operations. The group whose operator is speculative is the simplest of all inconsequential discretional groups: for if we reflect and then reflect again we are back where we started: that is, the essential structure of the group is given by R2 = I: Where `R ' stands for the operation of reflection and `I ' stands for identity. It is evident that this group has the fewest possible basic elements and the simplest possible structure, except for the group whose sole member is the identity operator, which is trivial. The operations of rotation and displacement are both continuous: they differ in that if we rotate far enough we come back to where we started, whereas we can displace further and further without ever coming back. Rotation is a cyclic continuous group, displacement a serial continuous group, and these again are the simplest and most fundamental kinds of continuous group. We can define Projective, Affine and Elliptic Geometry (but not Hyperbolic Geometry at all easily) in terms of other groups, but these other groups are less simple and fundamental than the one based on reflection, rotation and displacement. And therefore Euclidean Geometry, which is invariant under the group based on these three operators, is, from a purely formal point of view, pre-eminent.
The appeal of the theory of groups is not, however, purely formal. We see things reflected in mirrors: we see things from different sides and turn them round; and we both ourselves move, and move other things. If we did not pick out properties that were invariant under reflection, rotation and displacement, we should be unable to recognise as the same what we see in a mirror and what we see when we look direct, what we see from one side and what we see from the other, and what we see from afar off and what we see from nearby. And if we did not pick out properties that were invariant under rotation and displacement, we could not form the concept of a material object, something we can push around without affecting its properties.
The first argument is somewhat Kantian, although interestingly opposed to recent interpretations of what Kant actually said. Ewing (1938) and Strawson (1966) have attempted to save Kant's account of geometry by maintaining that it is a priori true at least of phenomenal geometry - the geometry of our visual experience - that it is Euclidean. But this is just what the geometry of appearances is not. Let the reader look up at the four corners of the ceiling of his room, and judge what the apparent angle at each corner is; that is, at what angle the two lines where the walls meet the ceiling appear to him to intersect each other. If the reader imagines himself sketching each corner in turn, he will soon convince himself that all the angles are more than right angles, some considerably so. And yet the ceiling appears to be a quadrilateral. From which it would seem that the geometry of appearances is non-Euclidean, with the angles of a quadrilateral adding up to more than 360'. And so it is; except it does not worry us, because we never think of it, hardly ever notice it. It is quite difficult to elicit from a man the answer that the angle appears to be more than a right angle. Asked simply what the angle seems to be, he will say, immediately and simply, `A right angle, of course'. For the geometry of appearances is, somewhat fundamentally unthinkable. If we are talking to each other, we are necessarily occupying different positions, from which things characteristically appear differently. In particular, apparent angles, except those placed symmetrically between us, will appear different. Therefore we cannot refer to apparent angles and apparent shapes, except by artifice and subsidiarily. We must talk not about the elliptical appearances of the penny, whose eccentricity is different for speaker and for hearer, but about the round reality, which is equally circular for both. We have to talk about the real shape, not the apparent shape, meaning by `the real shape' that which is invariant as among all likely speakers and hearers; invariant, that is, under transformations of the Euclidean group.
Shape must be a primary quality. It is different with colour. The colour of objects - apart from a few such as those made of shot silk - does not vary with the point from which they are viewed. The only external circumstance that affects colour is illumination, and this varies characteristically (for stone-age man, at least) only slowly with time. In the course of any one conversation, the illumination will be the same for both throughout. Therefore both speaker and hearer can talk about apparent colours. It was not necessary (until the invention of artificial lighting) to make much distinction between colours as they appeared to be and colours as they really were. Colours could afford to be secondary qualities, in a way in which shapes could not.
So great is the pressure that the necessities of communication exert on our minds that not only do we have to talk about real shapes rather than apparent shapes, but we see them. Psychologists have discovered `The Phenomenal Regression to the Real Object' (Tholes (I93I), Gibson (1950), Zangwill (1950), Woodworth (1963)); even when we try to concentrate on apparent angles or apparent shapes, our eyes see them more as they really are. Although the penny looks elliptical, if we are asked to choose from a selection of ellipses of varying degrees of eccentricity the one that most closely matches the apparent shape of the penny, we choose an ellipse that is less elliptical and more round than the retinal image of the penny is. Even when we try not to, we reinterpret the visual stimuli as seeming to be something more invariant than they actually are. We cannot be phenomenalists even when we try, but are naive realists at heart, and cannot help attending to those features that are invariable from place to place and person to person rather than those that are variable and subjective. The psychologists bear Kant out: the objectivity of the world is, in part at least, imposed by us, in that we choose to notice just those features that are objective-that is, invariant.
Not only as spectators do we need to be Euclidean, but even more so as agents. We could not be agents if we were floating among amorphous clouds; and in fact if we are to conceive of a stable world in which we can make more or less permanent alterations, we will want to preserve Euclidean invariance. Helmholtz (i876) was attempting to make this point in his axiom of Free Mobility: but his expression of it was open to the objection of Land (1877) and later of Russell that in basing Euclidean Geometry on the notion of rigidity, he was basing Geometry on Mechanics and putting the cart before the horse. `What is meant by the non-rigidity of a body?' asks Russell (1897) and answers `We mean, simply, that it has changed its shape. But this involves the possibility of comparison with its former shape, in other words, of measurement. In order, therefore, that there may be any question of rigidity or non-rigidity, the measurement of spatial magnitudes must be already possible. It follows that measurement cannot, without a vicious circle, be itself derived from experience of rigid bodies.' The objection is a fair one, against any attempt to build up a theory of space in terms of rigid measuring rods. And since Russell wrote The Foundations of Geometry, we have learned to be even more chary of assumptions about rigidity. But Euclidean Geometry need not be seen as the consequence of there actually being perfectly rigid bodies but as the precondition of its being conceptually possible for bodies to be more or less rigid. Measuring rods may or may not be rigid in the event: but there would be no sense in even thinking of using them unless we thought within a geometry in which there could be objects whose geometrical properties were unchanged by rotation and displacement. With rigidity, as with shape, Euclidean Geometry provides the only ecological environment in which it is a viable concept.
In trying to show how Euclidean Geometry is a condition of our experience as passive spectators, as active-or at least mobile-spectators, and as agents. It may be felt that this somewhat Kantian enterprise is still unsatisfactory-perhaps contaminated, in some obscure way, by psychologism. I therefore turn to an entirely different justification of Euclidean Geometry, which requires no Copernican revolution, and which would appeal as much to a Platonic Deity contemplating the Forms as to any sublunary philosophers conscious of the fact that they have eyes and hands.
The culmination of Euclid's first book of Elements is the proof of Pythagoras' Theorem . His proof is not easy. He was not able to use the much simpler proof, depending on similar triangles, because he did not have an adequate theory of proportion, which we, thanks to Cantor and Dedekind, do have. Correspondingly, the reverse chain of argument from Pythagoras' Theorem to the axiom of parallels is somewhat cumbersome, but if the reader will take on trust that the Wallis-Saccheri axiom `There exist two unequal triangles with equal angles' is equivalent to the axiom of parallels, then the following proof should convince him that so also is Pythagoras' proposition. Suppose we are given Pythagoras' proposition as an axiom, and all the axioms of Euclidean Geometry except the axiom of parallels. Let ABC and ABD be two isosceles right-angle triangles, with right angles at B. Then CBD is a straight line, and / ACB = ADB = / CAB. By Pythagoras AC2 = AB2 +BC2; AD2 = AB2 +BD2 AC2+AD2 =BC2+BD2 + 2AB2 =CD2 ; therefore /CAD is a right angle; therefore triangle CAD and triangle ABC are equiangular, but of different sizes; which is Saccheri's postulate, and from which the ordinary axiom of parallels can be proved?
Thus can regard Pythagoras' proposition as the distinctive feature of Euclidean geometry, instead of the axiom of parallels. It seems a much more fundamental one. It connects the concept of distance with that of a right angle - orthogonality - and it does so in the simplest possible way. If we have any metrical space of more than one dimension we are faced with the problem of how to combine measures in different dimensions: if a place is three miles East of us and four miles North, what distance is to be assigned to the direct route? A straight addition rule (i.e. one that would give the answer `seven') would be tantamount to a reduction to only one dimension of measurement. A `squares' rule is the next simplest, and fulfils all the conditions we require of any rule for combining measures. In particular, it has the merit (which it shares with the formulae of the fourth, sixth and eighth degree) of obliterating distinctions of sign-three miles East and four South will be five miles away just the same as three miles East and four North-which suits the essentially nonnegative nature of the concept of distance. Other rules could be adopted, might even be forced on us: but if we have the chance of adopting the Pythagorean rule, no further justification is needed. Mathematicians investigating differential geometries, which are not Euclidean, take care to posit nonetheless that they are `Locally Euclidean', that is to say that:
ds2 = d1x2+d2x2 + . . . + dxn2,
The concession, though indeed on a small scale, could hardly be larger. More fundamentally, we could defend the Pythagorean rule for being the simplest case of Parseval's Theorem. Parseval's Theorem is concerned with the Fourier expansion of functions (satisfying certain conditions of boundedness or measurability) in terms of cosine and sine functions. The Fourier expansion is (x) = 1/2ao + Sigma ancos nx + Sigma bnsin nx n=1 n=1 an and bn are known as the Fourier coefficients, and are given by the equations [omitted] and are thus independent of x, though determined, of course by f. Parseval’s Theorem states: 1 over pi integral from 0 to 2pi (f(x))2dx = 1/2ao2, Sigma (an2 + b, 2 ) n=, provided that in the internal provided that the interval [0,2pi] f(x) is measurable and (f(x))2 is fundamentally integral.
The Fourier expansion shows how a function f(x) may be plotted in a `phase-space' in terms of its Fourier coefficients - its `co-ordinates' and a set of fundamental functions - `the axes' of the space. It will be a `space' with a denumerably infinite number of dimensions, corresponding to the basic functions cos nx and sin nx (n = 0, 1, 2 . . . . ), and every function will be represented by a set of values for a0,a1,b1,a2,b2, . . . And then Parseval's Theorem shows that the integral of the square of the function, which we might regard as the square of the vector representing the function in phase-space, i.e. the square of the distance from the origin to the point (ao, a1, b1, a2, b2, . . . . ) is (barring slight terminological difficulties with the first term) the sum of the squares of the co-ordinates? It is a result entirely uncontaminated by geometrical intuition. The notion of space is an entirely abstract one of independent parameters; the basic trigonometrical functions can be defined exponentially; measure theory is purely analytical. So that a mathematician who was so pure as never to descend into geometry, and who had never heard of Euclid or Pythagoras, would still want to have a Pythagorean rule in Hilbert space, and still pay his respects to Euclidean orthodoxy.
The Euclidean geometry is the basic geometry. All other geometries are obtained as a modification of the proper Euclidean geometry. On one hand, the proper Euclidean geometry is a science on mutual disposition of points and geometric objects in the space. This disposition is described by the metric r (P,P') (distance) between two points P and P' of the space, or by the world function: s (P,P')=r2 (P,P')/2. On the other hand, the proper Euclidean geometry is a construction built on the foundation of some self-evident axiomatic. The proper Euclidean can be modified in two directions (1) One can modify the proper Euclidean geometry, changing world function s and using the fact that the proper Euclidean geometry is described completely by means of the world function. Any such a change of the world function is a deformation of the space. Geometry, appearing as a result of such a deformation, will be referred to as the physical geometry. (2) One can modify the proper Euclidean geometry, changing axiomatically of the Euclidean geometry. Geometry, appearing as a result of this modification, will be referred to as the mathematical geometry.
Maybe, terms 'mathematical geometry' and 'physical geometry' are not completely apposite, but distinguishing between the two kinds of geometries is necessary and not to confuse them.
Examples of mathematical geometries are the geometry of Lobachevsky, the projective geometry, the symplectic geometry, etc. These geometries are not relevant to the space and the space-time, or their relation to the space is indirect. Mathematical geometries are not interesting for physicists, and we will not consider them.
The physical geometries describe mutual disposition of geometrical objects in the space, or in the space-time. They are very interesting for physicists, because all physical phenomena evolve in the space-time, and configuration of the space-time appears to be very important for description of physical phenomena.
The remarkable property of the proper Euclidean geometry is that the proper Euclidean geometry can be completely described in terms of the world function, or in terms of the metric. It is the crucial point for construction of physical geometries. It means that all geometrical objects OE in the proper Euclidean geometry and all relations RE between them can be expressed in terms of the world function sE of the Euclidean space and only in its terms.
OE = OE (sE ), RE = RE (sE )
The world function sE of the Euclidean space have special properties and satisfies a set of conditions, written in terms of the world function. These conditions contains the integer parameter n, which can be interpreted as the dimension of the proper Euclidean space. There is a theorem that states that these conditions are necessary and sufficient conditions of the Euclideaness. According to this theorem all parameters of the Euclidean space (dimension, collinearity condition of two vectors, metric tensor, scalar product, coordinate system, etc.) can be expressed via the world function sE and only via it.
After deformation of the Euclidean space, when the world function sE of the Euclidean geometry GE is replaced by another world function sD , all geometrical objects OE = OE (sE ), and all relations
RE = RE (sE ) between them are transformed and another geometrical objects and another relations between them.
OE = OE (sE )® OD = OE (sD), RE = RE (sE )® RD = RE (sD)Gometrical objects OD = OE (sD ) and relations between them RD = RE (sD)) are geometrical objects and relations between them of another physical geometry GD , which is described completely by the world function sD. Geometrical object OD = OE (sD ) in geometry GD correspond to the geometrical object OE = OE (sE ) in the Euclidean geometry GE. In other words, the physical geometry GD is as pithy, as the Euclidean geometry, because the geometry GD contains all geometrical objects, which are contained in the Euclidean geometry.
Thus, using deformation of the Euclidean geometry and the fact that the world function describes the Euclidean geometry completely, we can construct a physical geometry with any metric structure (with any distances between its points). The obtained deformed geometry GD is as consistent as the proper Euclidean geometry GE, because in the physical geometry GD there are no its own axioms, theorems and statements. All relations between geometrical objects are taken from the Euclidean geometry in the deformed form. The only real problem of constructing a physical geometry is a writing of the Euclidean relations in the s-immanent form, i.e. in terms and only in terms of the world functions.
There are some subtleties in such a writing in the s-immanent form. The fact is that, that the world function sE of Euclidean space has its own specific Euclidean properties, and these properties must not be used at writing in the s-immanent form. These specific Euclidean properties are written for n-dimensional Euclidean space. They contain a reference to the dimension n of the Euclidean space. If we use them for definition of the geometric object O, the definition of the object O will contain parameter n, which has nothing to do with the geometrical object O.
For instance, the straight line TPP' in the proper Euclidean space is defined by two its points P and P'. The relation, defining the straight line TPP', has not to depend on dimension of the Euclidean space. The straight line is defined by the relation:
TPP'={R
PP'
PR},
where R is the running point of the set TPP' and condition PP'
PR means that vectors PP' and PR are collinear, i.e. the scalar product (PP'.PR) of these two vectors satisfies the relation (1) (PP'.PR)2=(PP'.PP') (PR.PR)º
PP'
2
PR
2.
The scalar product is defined via the world function by the relation
(PP'.PR)= 0.5(
PP'
2+
PR
2-
P'R
2) º s (P,P')+s (P,R)-s (P',R)
Thus, the straight line is defined s-immanently, i.e. in terms of the world functions.
In the Euclidean geometry one can use another definition of collinearity. Condition of collinearity is satisfied, if components of vectors PP' and PR in some coordinate system are proportional. For instance, in the 3-dimensional Euclidean space one can introduce rectangular coordinate system, choosing four points P3={P,P1,P2,P3} and forming three basic vectors PPa , a =1,2,3. Then the collinearity condition can be written in the form of three equations, with two of them being independent.(2) (PPa .PP')=a (PPa .PR), a =1,2,3,.
Here a is some constant. Relations (2) are relations for covariant components of vectors PP' and PR in the considered coordinate system with basic vectors PPa , a =1,2,3. Then equations (1), (2), and:
T(P,P',P1,P2,P3)={R
PP'
PR},
determine the geometrical object that depends on five points P,P',P1,P2,P3. This geometrical object describes a complex, consisting of the straight line and the coordinate system, represented by four points P3 ={P,P1,P2,P3}. In the Euclidean space dependence on the choice of the coordinate system and three points P1,P2,P3 determining this system, is fictitious. The geometrical object T(P,P',P1,P2,P3) depends only on two points P,P' and coincides with the straight line TPP'. However, at deformations of the Euclidean space the geometrical objects T(P,P',P1,P2,P3) and TPP' are deformed differently. The points P1,P2,P3 cease to be fictitious in definition of T(P,P',P1,P2,P3), and objects T(P,P',P1,P2,P3) and TPP' become to be different geometric objects, overall.
Which of two geometrical objects should be interpreted as the straight line, passing through the points P,P' in the deformed geometry GD? Of course, the straight line is TPP' , because its definition does not contain a reference to a coordinate system, whereas definition of T(P,P',P1,P2,P3) depends on the choice of the coordinate system. Collectively, the definition of geometric objects and relations between them may not refer to the means of description.
However, in the given case the geometrical object TPP' is, in general, two-dimensional surface, whereas T(P,P',P1,P2,P3) is intersection of two-dimensional surfaces, i.e., T(P,P',P1,P2,P3) is, in general, a one-dimensional curve. The one-dimensional curve T(P,P',P1,P2,P3) corresponds better to our ideas on the straight line, than the two-dimensional surface TPP'. Nonetheless, it is TPP', that is analog of the Euclidean straight line in geometry GD.
Overcoming our conventional idea that the Euclidean straight line cannot be deformed into many-dimensional surface is very difficult, and this idea has been preventing for years from construction of the physical geometries.
Practically one chooses such physical geometries, where deformation of the Euclidean space transform the Euclidean straight lines into one-dimensional lines. It means that one choose such a geometries, where geometrical objects TPP' and T(P,P',P1,P2,P3) coincide. (3) TPP' =T(P,P',P1,P2,P3)
Riemannian geometries satisfy this condition. The Riemannian geometry is a kind of physical geometry that is constructed on the basis of the deformation principle, when the infinitesimal Euclidean interval dS(E)2=g(E)ikdxidxk is deformed into the Riemannian interval dS(R)2=g(R)ikdxidxk. Deformation is chosen in such a way that any Euclidean straight line T(E)PP' , passing through the point P, collinearly to the vector PP' coincide with the geodesic T(R)PP' , passing through the point P, collinear to the vector PP' in the Riemannian space. Condition (3) of coincidence of objects TPP' and T(P,P',P1,P2,P3) restricts class of possible physical geometries, reducing it to the class of Riemannian geometries.
Note that in physical geometries, satisfying the condition (3), the straight line TQ;P''P', passing through the point Q collinear to the vector PP', is not a one-dimensional line, in general. If the Riemannian geometries be strictly physical geometries, then they would contain non-one-dimensional geodesics (straight lines). Nevertheless, the Riemannian geometries are not strictly physical geometries, because at their construction one uses not only the deformation principle, but another methods, containing a reference to the means of description. In particular, in the Riemannian geometries absolute parallelism is absent, and one cannot to define a straight line, passing through the point Q collinear to the vector PP', provided points P and Q do not coincide. On one hand, lack of absolute parallelism allows one to go around the problem of non-one-dimensional straight lines. On the other hand, it makes the Riemannian geometries to be inconsistent, because they cease to be physical geometries. The Metric conception of geometry (MCG) the geometry is determined on any point set M by setting real functions G(P, P) with the properties G(P, P)=G(P’, P’)=0. The function G(P, P) is called the world function, and the geometry determined by the world function is called tubular geometry, or shortly T-geometry. All relations of T-geometry are derived as relations of proper Euclidean geometry written in terms of the world function. Vector PQ of T-geometry is the ordered set of points PQ={P, Q}. Its length is
PQ
=G(P,Q) The scalar product (PQ, RS) of two vectors PQ and RS )
(PQ.RS)=G(P,S)+G(R,Q)-G(P,R)-G(Q,S)
PQ
=G(P,Q)
The scalar product (PQ, RS) of two vectors:
Q and RS ) (PQ.RS)=G(P,S)+G(R,Q)-G(P,R)-G(Q,S).
In this has the form (one special case, when the points P and R coincide, one has: (2)
Q.PS)=G(P,S)+G(P,Q)-G(Q,S)
which means the cosine theorem for the triangle with vortices at the has the form (1)
(PQ.RS)=G(P,S)+G(R,Q)-G(P,R)-G(Q,S)(PQ.RS)=G(P,S)+G(R,Q)-G(P,R)-G(Q,S)
In the special case, when the points P and R coincide, one has: (2)
Q.PS)=G(P,S)+G(P,Q)-G(Q,S)
which means the cosine theorem for the triangle with vortices at the points P,Q,S.? When two vectors P_0P_1and Q_0Q_1 are parallel, provided the angle a between them is equal to zero, i.e. (3) cosa=(P_0P_1.Q_0Q_1)/(
P_0P_1
Q_0Q_1
)=1. Taking into account that
P_0P_1
P_0P_1
=(P_0P_1.P_0P_1), this condition can be written in the form of the second order Gram's determinant:
(4) det
(P_0P_i .Q_0Q_k)
=0, i,k=1,2
In general, the condition (4) is not so strong, as the condition (3), it means that vectors P_0P_1 and Q_0Q_1 are linearly dependent (collinear P_0P_1
Q_0Q_1 , i.e. parallel, or antiparallel). In general,
in the proper Euclidean space n vectors P_0P_i, i=1,2,. . . .n are linearly dependent, if and only if the nth order Gram's determinant vanishes: (5) F_n(P^n)=det
(P_0P_i .P_0P_k)
=0, k=1,2, . . . /n. Thus, in virtue of (2) the necessary and sufficient condition of the linear dependence of n vectors P_0P_i, i=1,2,. . . .n is written in terms of only world function, without referring to linear space. The formulation of the linear dependence condition contains only several points of the space and the world function between them. The proper Euclidean geometry can be described completely in terms of the world function and finite sets of points P^n={P_0,P_1, . . . P_n}. Such a description of geometry will be referred to as sigma-immanent description. At such a description of the Euclidean geometry the world function is to satisfy some sigma-immanent conditions (1)-(3)
One can prove the following theorem as to the sigma-space V={M,G} is the Euclidean space, are fulfilled. This theorem means that information, concluded in the world function is sufficient for construction of the Euclidean geometry. This information is sufficient also for construction of a geometry, if conditions (1)-(3), specific for Euclidean geometry are not satisfied. Any world function associates with some geometry (T-geometry).
In particular, in any geometry n points P^n={P_0,P_1} P_n}, which do not satisfy the condition (5) determines the nth order natural geometric object (NGO). This object, called the nth order tube, is the set T(P^n) of points, defined by the relation: (6) T(P^n)={P_(n+1)
F_(n+1)(P^(n+1))=0}
In the case of the proper Euclidean geometry the nth order tube T(P^n) is the n-dimensional plane. In the case of two points P_0, P_1 the first order tube T(P_0P_1 ) is the straight line, passing through points P_0, P_1. Changing the Euclidean world function G_E, one obtains disported Euclidean space with the world function G_D. In this more general case, when conditions (1)-(3) are not fulfilled, and T-geometry is not the Euclidean one, the tube T(P_0P_1 ) is a hallow (m-1)-dimensional tube (m is the dimension of the space), but not a line. The T-geometry with world function (7) G_D=G_E+D(G_D), where D is some function, is nondegenerate T-geometry. In such a geometry the segment T([P_P 1 ])of the tube T(P_P.) between points P.0, P.1 has the cigar like shape. This ‘cigar’ is a set of ends R of the vector P_R, parallel to the vector P_0P.1 . In the proper Euclidean space there is only one vector P_0R of fixed length
P_0R
, which is parallel to the vector P.0P_1. In the distorted space V_D with the world function G_D there is a set of many such vectors. The ends of the vectors P_0R form the ‘cigar’. The T-geometry, where there are many vectors P_0R of fixed length parallel to the vector P_0P_1 is nondegenerate geometry. Under some world functions the (m-1)-dimensional "cigars" T([P_0P_1 ]) may degenerate into a curves, and one obtains a degenerate T-geometry.
Natural geometrical objects (NGO) are sets of points determined by the geometry and several parameters (basic points of NGO). Points of the space are parameters of NGOs. Any geometry is described by their natural geometric objects (NGO). The order of NGO is determined by the number of basic points. In the proper Euclidean geometry the point P is the zeroth order NGO defined by one parameter (the same point P). The straight L(P,Q) is the first order NGO defined by two different points P,Q. The plane L(P,Q,R) is the second order NGO, defined by three different points P,Q,R that do not lee on one straight. In other geometries NGOs have another form, but they are always defined by corresponding geometry. For instance, in the Riemannian geometry the first order NGO is a geodesic. Description of a geometry in terms of its NGOs is the most adequate way of construction of the geometry. For instance, the proper Euclidean geometry is described conventionally in terms of points, straights, planes, (i.e. in terms of its NGOs). In the proper Euclidean geometry NGOs are defined by their properties by means of axioms. On the other hand, if distances S=S(P,Q) between all pairs of points P,Q are given, the NGOs of Euclidean geometry can be defined via distances. In this case the axioms describing properties of NGOs turn to theorems, and geometry is defined by the form of the distance function S=S(P,Q). Practically it is more convenient to use instead of S=S(P,Q) the so-called world function:
G(P,Q) = S(P,Q) S(P,Q)/2
which is always real, even so the geometry is the Minkowski geometry.
Geometry of any space may be considered as a result of a deformation of the proper Euclidean geometry, when one changes distances S=S(P,Q) between the space points P, Q. Any such deformation changes the shape of NGOs. On the other hand, any geometry is some kind of generalization of the proper Euclidean geometry. The way of generalization of the Euclidean geometry depends essentially on the way of definition of the Euclidean straight (the first order NGO). If the Euclidean straight L(P,Q) is defined as shortest line between the points P,Q , determining L(P,Q), one obtains the Riemannian geometry. If the Euclidean straight L(P,Q) is defined by its collimetric property as a set of points, one obtains the T-geometry (or tubular geometry, or geometry of tubes). The term ‘collimetric’ is constructed of two terms ‘collinear’ and ‘metric’. Collimetric property means the collinearity of two vectors RP and RQ expressed via distances between points P_Q_R. Mathematically collinearity RP
RQ is expressed by means of the relation
(RP.RQ)(RP.RQ) = (RP.RP)(RQ.RQ)
where according to the cosine theorem the scalar product (RP.RQ) of vectors RP and RQ can be expressed via their lengths
RP
and
RQ
, or via world function:
G(P,Q) = S(P,Q) S(P,Q)/2
by the relation:
(RP.RQ) = G(R,P) + G(R,Q) -- G(P,Q)
The Riemannian geometry is such a generalization of the proper Euclidean geometry that uses definition of the first order NGO as the shortest line. This generalization to the Euclidean geometry is based on two structures: the topological structure and the metric one. The fact is that the concept of a line needs a definition, and this definition is carried out via topological properties that are introduced independently of the metric properties. As a result the Riemannian geometry is a geometry based on two structures.
The T-geometry is a generalization of the proper Euclidean geometry that uses the definition of the first order NGO as a set of points having the collimetric property. The set of points does not need an additional definition. As a result the T-geometry is a geometry based on only metric structure. The T-geometry is more general and simpler than the Riemannian geometry. T-geometry contains the Riemannian geometry as a special case. On the other hand the first order NGO defined as a set of points is not a line in general. The first order NGO in T-geometry appears to be a hallow tube. In some cases these tubes can degenerate into one-dimensional lines. Then one obtains degenerate geometries (Riemannian and Euclidean).
Nondegenerate geometry is another name for the T-geometry. In the T-geometry the first order tube T_{P,Q} (the first order NGO) is determined by the points P and Q as the set of running points R:
T_{PQ} = (R
RP
RQ ) = (R
(RP.RQ)(RP.RQ) = (RP.RP)(RQ.RQ))
where all scalar products can be expressed via the world function by means of the relation:
(RP.RQ) = G(R,P) + G(R,Q) -- G(P,Q).
It is clear intuitively that the whole geometry can be constructed, if one can construct NGO. It is clear in the case of the proper Euclidean geometry. It is so in the case of a general geometry defined by an arbitrary world function G(P,Q).
For degenerate geometries (Euclidean, Riemannian, Minkowski) the first order tube T_{P,Q} degenerates into one-dimensional line L_{P,Q} due to extremal properties of the world function. In this case it is possible to construct a manifold, to determine the dimensionality of the space and introduce a coordinate system construction of the manifold on the basis of the metric means that in some cases it is possible to construct the topological structure on the basis of the metric one.
In the general case it is impossible to construct a manifold. A mathematical technique of work with a nondegenerate geometry is not yet developed. But in the case, when the real world function is distinguished slightly from that of the Minkowski space, one can use approximately the relation
G=G_M+D,
where G_M is the world function of the Minkowski space and D is a distortion function describing a degree of nondegeneracy of the space-time.
In this case it is possible to construct a manifold on the base of G_M, to introduce a coordinate system and to consider the distortion function D=D(P,Q) as some two-point field in the Minkowski space-time. If the real space-time is uniform and isotropic, the distortion function is a function of only G_M:
D=D(G_M)
In the space-time with the non-vanishing distortion D a world tube of a real particle of the mass m is defined as a broken tube consisting of segments T_[P,P'] of the same length. The length of the segments is proportional to the mass m of the particle. Thus, the mass of a particle becomes a geometrical quantity. As a result of the non-vanishing distortion the relative position of two adjoining segments is not fixed, (although the hyperbolic cosine of the angle between them for a free particle is equal to one). In this sense the world tube of a real particle is stochastic. The stochasticity is the more intensive the less the mass of the particle.
By definition a statistical description of a stochastic system S_st is a replacement of a description of a single stochastic system S_st by a description of N independent identical systems S_st (with N tending to infinity). As a result of such a replacement a deterministic dynamic system E[S_st] arises. E[S_st] is known as a statistical ensemble of stochastic systems S_st.
Experiments with a single S_st are irreproducible, whereas experiments with E[S_st] are reproducible. In other words, a result of a single experiment is irreproducible, but distributions of results are reproducible.
The principal goal of the statistical description is a construction of E[S_st] as a dynamic system. If such a dynamic system E[S_st] has been constructed, then, investigating this dynamic system, one can calculate and explain all results of reproducible experiments with S_st (in reality with ensembles of S_st ). There is no general way of the construction of the dynamic system E[S_st], corresponding to the stochastic system S_st.
The statistical description in itself does not need any probabilistic constructions. These probabilistic constructions (the statistical ensemble as a tool for calculation of average values) are needed only for interpretation of the E[S_st] dynamics and experiments with E[S_st] in terms of the mean behaviour of the stochastic system S_st. Such an interpretation has also a heuristic meaning.
If the distortion function has asymptotic value D = h/b, where h is the quantum constant and b is some universal constant connecting the usual mass of the particle with the length of the world tube segment T_[P,P'], the statistical description of stochastic world tubes coincides with the quantum description (Schrödinger equation).
Schrödinger's great discovery of wave mechanics originated with the work of French physicist Louis de Broglie. In 1923 de Broglie used ideas from German American physicist Albert Einstein’s special theory of relativity to show that an electron, or any other particle, has a wave associated with it. De Broglie’s work resulted in the equation, showing ? = h/p, where ? is the wavelength of the associated wave, h is a number called Planck's constant, and p is the momentum of the particle? Physicists immediately deduced that if particles (particularly electrons) have waves, then a particular type of partial differential equation known as a wave equation should be able to describe their behaviour. These ideas were taken up by both de Broglie and Schrödinger, and in 1926 each published the same wave equation. Unfortunately, while the equation is true, it was of very little help in explaining the behaviours of particles.
Later the same year Schrödinger used a new approach. He studied the mathematics of partial differential equations and the Hamiltonian function, a powerful idea in mechanics developed by British mathematician Sir William Rowan Hamilton in the mid-1800's. Schrödinger formulated an equation in terms of the energy of the electron and the energy of the electric field in which it was situated. Partial differential equations have many solutions, but solutions to Schrödinger’s equation had to meet strict conditions to be useful in describing the electron. Among other things, they had to be finite and possess only one value. These solutions were associated with special values of the electron’s energy level, known as proper values or eigenvalues.
Schrödinger solved the equation for the hydrogen atom, V = –e2/r, in which V is the energy of the electric field surrounding the electron, e is the electron's charge, and r is its distance from the atom’s nucleus. He found that the eigenvalues of the electron’s energy corresponded with those of the energy levels given in the older theory of Danish physicist Niels Bohr. Bohr’s theory of the atom described electrons orbiting atoms in strict circular orbits at particular distances that corresponded to specific levels of energy. In the hydrogen atom (which consists of one electron and one proton), the wave function Schrödinger derived instead describes where physicists are most likely to find the electron. The electron is most likely to be where Bohr predicted it to be, but it does not follow a strictly circular orbit. The electron is described by the more complicated notion of an orbital - a region in space where the electron has varying degrees of probability of being found.
Schrödinger's wave equation can describe atoms other than hydrogen as well as molecules and ions (atoms or molecules with electric charge), but such cases are very difficult to solve. In a few such cases physicists have found approximate solutions, usually with a computer carrying out the numerical work.
Schrödinger's mathematical description of electron waves found immediate acceptance. The mathematical description matched what scientists had learned about electrons by observing them and their effects. In 1925, a year before Schrödinger published his results, German-British physicist Max Born and German physicist Werner Heisenberg developed a mathematical system called matrix mechanics. Matrix mechanics also succeeded in describing the structure of the atom, but it was totally theoretical. It gave no picture of the atom that physicists could verify observationally. Schrödinger's vindication of de Broglie's idea of electron waves immediately overturned matrix mechanics, though later physicists showed that wave mechanics is equivalent to matrix mechanics.
To solve these problems, mathematicians use calculus, which deals with continuously changing quantities, such as the position of a point on a curve. Its simultaneous development in the 17th century by English mathematician and physicist Isaac Newton and German philosopher and mathematician Gottfried Wilhelm Leibniz enabled the solution of many problems that had been insoluble by the methods of arithmetic, algebra, and geometry. Among the advances that calculus helped develop were the determinations of Newton’s laws of motion and the theory of electromagnetism.
The physical sciences investigate the nature and behaviour of matter and energy on a vast range of size and scale. In physics itself, scientists study the relationships between matter, energy, force, and time in an attempt to explain how these factors shape the physical behaviour of the universe. Physics can be divided into many branches. Scientists study the motion of objects, a huge branch of physics known as mechanics that involves two overlapping sets of scientific laws. The laws of classical mechanics govern the behaviour of objects in the macroscopic world, which includes everything from billiard balls to stars, while the laws of quantum mechanics govern the behaviour of the particles that make up individual atoms.
The new math is new only in that the material is introduced at a much lower level than heretofore. Thus geometry, which was and is commonly taught in the second year of high school, is now frequently introduced, in an elementary fashion, in the fourth grade - in fact, naming and recognition of the common geometric figures, the circle and the square, occur in kindergarten. At an early stage, numbers are identified with points on a line, and the identification is used to introduce, much earlier than in the traditional curriculum, negative numbers and the arithmetic processes involving them.
The elements of set theory constitute the most basic and perhaps the most important topic of the new math. Even a kindergarten child can understand, without formal definition, the meaning of a set of red blocks, the set of fingers on the left hand, and the set of the child’s ears and eyes. The technical word set is merely a synonym for many common words that designate an aggregate of elements. The child can understand that the set of fingers on the left hand and the set on the right hand match - that is, the elements, fingers, can be put into a one-to-one correspondence. The set of fingers on the left hand and the set of the child’s ears and eyes do not match. Some concepts that are developed by this method are counting, equality of number, more than, and less than. The ideas of union and intersection of sets and the complement of a set can be similarly developed without formal definition in the early grades. The principles and formalism of set theory are extended as the child advances; upon graduation from high school, the student’s knowledge is quite comprehensive.
The amount of new math and the particular topics taught vary from school to school. In addition to set theory and intuitive geometry, the material is usually chosen from the following topics: a development of the number systems, including methods of numeration, binary and other bases of notation, and modular arithmetic; measurement, with attention to accuracy and precision, and error study; studies of algebraic systems, including linear algebra, modern algebra, vectors, and matrices, with an axiomatic as well as traditional approach; logic, including truth tables, the nature of proof, Venn or Euler diagrams, relations, functions, and general axiomatic; probability and statistics; linear programming; computer programming and language; and analytic geometry and calculus. Some schools present differential equations, topology, and real and complex analysis.
Cosmology, of an evolution, is the study of the general nature of the universe in space and in time - what it is now, what it was in the past and what it is likely to be in the future. Since the only forces at work between the galaxies that make up the material universe are the forces of gravity, the cosmological problem is closely connected with the theory of gravitation, in particular with its modern version as comprised in Albert Einstein's general theory of relativity. In the frame of this theory the properties of space, time and gravitation are merged into one harmonious and elegant picture.
The basic cosmological notion of general relativity grew out of the work of great mathematicians of the 19th century. In the middle of the last century two inquisitive mathematical minds - Russian named Nikolai Lobachevski and a Hungarian named János Bolyai - discovered that the classical geometry of Euclid was not the only possible geometry: in fact, they succeeded in constructing a geometry that was fully as logical and self-consistent as the Euclidean. They began by overthrowing Euclid's axiom about parallel lines: namely, that only one parallel to a given straight line can be drawn through a point not on that line. Lobachevski and Bolyai both conceived a system of geometry in which a great number of lines parallel to a given line could be drawn through a point outside the line.
To illustrate the differences between Euclidean geometry and their non-Euclidean system it is simplest to consider just two dimensions - that is, the geometry of surfaces. In our schoolbooks this is known as "plane geometry," because the Euclidean surface is a flat surface. Suppose, now, we examine the properties of a two-dimensional geometry constructed not on a plane surface but on a curved surface. For the system of Lobachevski and Bolyai we must take the curvature of the surface to be ‘negative’, which means that the curvature is not like that of the surface of a sphere but like that of a saddle. Now if we are to draw parallel lines or any figure
(e.g., a triangle) on this surface, we must decide first of all how we shall define a ‘straight line’, equivalent to the straight line of plane geometry. The most reasonable definition of a straight line in Euclidean geometry is that it is the path of the shortest distance between two points. On a curved surface the line, so defined, becomes a curved line known as a ‘geodesic’.
Considering a surface curved like a saddle, we find that, given a ‘straight’ line or geodesic, we can draw through a point outside that line a great many geodesics that will never intersect the given line, no matter how far they are extended. They are therefore parallel to it, by the definition of parallel. The possible parallels to the line fall within certain limits, indicated by the intersecting lines.
As a consequence of the overthrow of Euclid's axiom on parallel lines, many of his theorems are demolished in the new geometry. For example, the Euclidean theorem that the sum of the three angles of a triangle is 180 degrees no longer holds on a curved surface. On the saddle-shaped surface the angles of a triangle formed by three geodesics always add up to less than 180 degrees, the actual sum depending on the size of the triangle. Further, a circle on the saddle surface does not have the same properties as a circle in plane geometry. On a flat surface the circumference of a circle increases in proportion to the increase in diameter, and the area of a circle increases in proportion to the square of the increase in diameter. But on a saddle surface both the circumference and the area of a circle increase at faster rates than on a flat surface with increasing diameter.
After Lobachevski and Bolyai, the German mathematician Bernhard Riemann constructed another non-Euclidean geometry whose two-dimensional model is a surface of positive, rather than negative, curvature - that is, the surface of a sphere. In this case a geodesic line is simply a great circle around the sphere or a segment of such a circle, and since any two great circles must intersect at two points (the poles), there are no parallel lines at all in this geometry. Again the sum of the three angles of a triangle is not 180 degrees: in this case it is always more than 180. The circumference of a circle now increases at a rate slower than in proportion to its increase in diameter, and its area increases more slowly than the square of the diameter.
Now all this is not merely an exercise in abstract reasoning but bears directly on the geometry of the universe in which we live. Is the space of our universe ‘flat’, as Euclid assumed, or is it curved negatively (per Lobachevski and Bolyai) or curved positively (Riemann)? If we were two-dimensional creatures living in a two-dimensional universe, we could tell whether we were living on a flat or a curved surface by studying the properties of triangles and circles drawn on that surface. Similarly as three-dimensional beings living in three-dimensional space, in that we should be capably able by way of studying geometrical properties of that space, to decide what the curvature of our space is. Riemann in fact developed mathematical formulas describing the properties of various kinds of curved space in three and more dimensions. In the early years of this century Einstein conceived the idea of the universe as a curved system in four dimensions, embodying time as the fourth dimension, and he proceeded to apply Riemann's formulas to test his idea.
Einstein showed that time can be considered a fourth coordinate supplementing the three coordinates of space. He connected space and time, thus establishing a ‘space-time continuum’, by means of the speed of light as a link between time and space dimensions. However, recognizing that space and time are physically different entities, he employed the imaginary number Á, or i, to express the unit of time mathematically and make the time coordinate formally equivalent to the three coordinates of space.
In his special theory of relativity Einstein made the geometry of the time-space continuum strictly Euclidean, that is, flat. The great idea that he introduced later in his general theory was that gravitation, whose effects had been neglected in the special theory, must make it curved. He saw that the gravitational effect of the masses distributed in space and moving in time was equivalent to curvature of the four-dimensional space-time continuum. In place of the classical Newtonian statement that ‘the sun produces a field of forces that impels the earth to deviate from straight-line motion and to move in a circle around the sun’. Einstein substituted a statement to the effect that ‘the presence of the sun causes a curvature of the space-time continuum in its neighbourhood’.
The motion of an object in the space-time continuum can be represented by a curve called the object's ‘world line’. Einstein declared, in effect: "The world line of the earth is a geodesic in the curved four-dimensional space around the sun." In other words, the . . .earth’s ‘world line’ . . . corresponds to the shortest four-dimensional distance between the position of the earth in January . . . and its position in October . . .
Einstein's idea of the gravitational curvature of space-time was, of course, triumphantly affirmed by the discovery of perturbations in the motion of Mercury at its closest approach to the sun and of the deflection of light rays by the sun's gravitational field. Einstein next attempted to apply the idea to the universe as a whole. Does it have a general curvature, similar to the local curvature in the sun's gravitational field? He now had to consider not a single centre of gravitational force but countless centres of attraction in a universe full of matter concentrated in galaxies whose distribution fluctuates considerably from region to region in space. However, in the large-scale view the galaxies are spread fairly uniformly throughout space as far out as our biggest telescopes can see, and we can justifiably ‘smooth out’ its matter to a general average (which comes to about one hydrogen atom per cubic metre). On this assumption the universe as a whole has a smooth general curvature.
But if the space of the universe is curved, what is the sign of this curvature? Is it positive, as in our two-dimensional analogy of the surface of a sphere, or is it negative, as in the case of a saddle surface? And, since we cannot consider space alone, how is this space curvature related to time?
Analysing the pertinent mathematical equations, Einstein came to the conclusion that the curvature of space must be independent of time, i.e., that the universe as a whole must be unchanging (though it changes internally). However, he found to his surprise that there was no solution of the equations that would permit a static cosmos. To repair the situation, Einstein was forced to introduce an additional hypothesis that amounted to the assumption that a new kind of force was acting among the galaxies. This hypothetical force had to be independent of mass (being the same for an apple, the moon and the sun) and to gain in strength with increasing distance between the interacting objects (as no other forces ever do in physics).
Einstein's new force, called ‘cosmic repulsion’, allowed two mathematical models of a static universe. One solution, which was worked out by Einstein himself and became known as, Einstein's spherical universe, gave the space of the cosmos a positive curvature. Like a sphere, this universe was closed and thus had a finite volume. The space coordinates in Einstein's spherical universe were curved in the same way as the latitude or longitude coordinates on the surface of the earth. However, the time axis of the space-time continuum ran quite straight, as in the good old classical physics. This means that no cosmic event would ever recur. The two-dimensional analogy of Einstein's space-time continuum is the surface of a cylinder, with the time axis running parallel to the axis of the cylinder and the space axis perpendicular to it.
The other static solution based on the mysterious repulsion forces was discovered by the Dutch mathematician Willem de Sitter. In his model of the universe both space and time were curved. Its geometry was similar to that of a globe, with longitude serving as the space coordinate and latitude as time. Unhappily astronomical observations contradicted both Einstein and de Sitter's static models of the universe, and they were soon abandoned.
In the year 1922 a major turning point came in the cosmological problem. A Russian mathematician, Alexander A. Friedman (from whom the author of this article learned his relativity), discovered an error in Einstein's proof for a static universe. In carrying out his proof Einstein had divided both sides of an equation by a quantity that, Friedman found, could become zero under certain circumstances. Since division by zero is not permitted in algebraic computations, the possibility of a nonstatic universe could not be excluded under the circumstances in question. Friedman showed that two nonstatic models were possible. One pictured the universe as expanding with time; the other, contracting.
Einstein quickly recognized the importance of this discovery. In the last edition of his book The Meaning of Relativity he wrote: "The mathematician Friedman found a way out of this dilemma. He showed that it is possible, according to the field equations, to have a finite density in the whole (three-dimensional) space, without enlarging these field equations. Einstein remarked to me many years ago that the cosmic repulsion idea was the biggest blunder he had made in his entire life.
Almost at the very moment that Friedman was discovering the possibility of an expanding universe by mathematical reasoning, Edwin P. Hubble at the Mount Wilson Observatory on the other side of the world found the first evidence of actual physical expansion through his telescope. He made a compilation of the distances of a number of far galaxies, whose light was shifted toward the red end of the spectrum, and it was soon found that the extent of the shift was in direct proportion to a galaxy's distance from us, as estimated by its faintness. Hubble and others interpreted the red-shift as the Doppler effect - the well-known phenomenon of lengthening of wavelengths from any radiating source that is moving rapidly away (a train whistle, a source of light or whatever). To date there has been no other reasonable explanation of the galaxies' red-shift. If the explanation is correct, it means that the galaxies are all moving away from one another with increasing velocity as they move farther apart.
Thus Friedman and Hubble laid the foundation for the theory of the expanding universe. The theory was soon developed further by a Belgian theoretical astronomer, Georges Lemaître. He proposed that our universe started from a highly compressed and extremely hot state that he called the ‘primeval atom’. (Modern physicists would prefer the term ‘primeval nucleus’.) As this matter expanded, it gradually thinned out, cooled down and reaggregated in stars and galaxies, giving rise to the highly complex structure of the universe as we know it today.
Until a few years ago the theory of the expanding universe lay under the cloud of a very serious contradiction. The measurements of the speed of flight of the galaxies and their distances from us indicated that the expansion had started about 1.8 billion years ago. On the other hand, measurements of the age of ancient rocks in the earth by the clock of radioactivity (i.e., the decay of uranium to lead) showed that some of the rocks were at least three billion years old; more recent estimates based on other radioactive elements raise the age of the earth's crust to almost five billion years. Clearly a universe 1.8 billion years old could not contain five-billion-year-old rocks! Happily the contradiction has now been disposed of by Walter Baade's recent discovery that the distance yardstick (based on the periods of variable stars) was faulty and that the distances between galaxies are more than twice as great as they were thought to be. This change in distances raises the age of the universe to five billion years or more.
Friedman's solution of Einstein's cosmological equation, permits two kinds of universe. We can call one the "pulsating" universe. This model says that when the universe has reached a certain maximum permissible expansion, it will begin to contract; that it will shrink until its matter has been compressed to a certain maximum density, possibly that of atomic nuclear material, which is a hundred million million times denser than water; that it will then begin to expand again - and so on through the cycle ad infinitum. The other model is a "hyperbolic" one: it suggests that from an infinitely thin state an eternity ago the universe contracted until it reached the maximum density, from which it rebounded to an unlimited expansion that will go on indefinitely in the future.
The question whether our universe is actually ‘pulsating’ or ‘hyperbolic’ should be decidable from the present rate of its expansion. The situation is analogous to the case of a rocket shot from the surface of the earth. If the velocity of the rocket is less than seven miles per second - the ‘escape velocity’ - the rocket will climb only to a certain height and then fall back to the earth. (If it were completely elastic, it would bounce up again, . . . and so on.) On the other hand, a rocket shot with a velocity of more than seven miles per second will escape from the earth's gravitational field and disappear in space. The case of the receding system of galaxies is very similar to that of an escape rocket, except that instead of just two interacting bodies (the rocket and the earth) we have an unlimited number of them escaping from one another. We find that the galaxies are fleeing from one another at seven times the velocity necessary for mutual escape.
Thus we may conclude that our universe corresponds to the ‘hyperbolic’ model, so that its present expansion will never stop. We must make one reservation. The estimate of the necessary escape velocity is based on the assumption that practically all the mass of the universe is concentrated in galaxies. If intergalactic space contained matter whose total mass was more than seven times that in the galaxies, we would have to reverse our conclusion and decide that the universe is pulsating. There has been no indication so far, however, that any matter exists in intergalactic space, and it could have escaped detection only if it were in the form of pure hydrogen gas, without other gases or dust.
Is the universe finite or infinite? This resolves itself into the question: Is the curvature of space positive or negative - closed like that of a sphere, or open like that of a saddle? We can look for the answer by studying the geometrical properties of its three-dimensional space, just as we examined the properties of figures on two-dimensional surfaces. The most convenient property to investigate astronomically is the relation between the volume of a sphere and its radius.
We saw that, in the two-dimensional case, the area of a circle increases with increasing radius at a faster rate on a negatively curved surface than on a Euclidean or flat surface; and that on a positively curved surface the relative rate of increase is slower. Similarly the increase of volume is faster in negatively curved space, slower in positively curved space. In Euclidean space the volume of a sphere would increase in proportion to the cube, or third power, of the increase in radius. In negatively curved space the volume would increase faster than this; in positively curved space, slower. Thus if we look into space and find that the volume of successively larger spheres, as measured by a count of the galaxies within them, increases faster than the cube of the distance to the limit of the sphere (the radius), we can conclude that the space of our universe has negative curvature, and therefore is open and infinite. By the same token, if the number of galaxies increases at a rate slower than the cube of the distance, we live in a universe of positive curvature - closed and finite.
Following this idea, Hubble undertook to study the increase in number of galaxies with distance. He estimated the distances of the remote galaxies by their relative faintness: galaxies vary considerably in intrinsic brightness, but over a very large number of galaxies these variations are expected to average out. Hubble's calculations produced the conclusion that the universe is a closed system - a small universe only a few billion light-years in radius.
We know now that the scale he was using was wrong: with the new yardstick the universe would be more than twice as large as he calculated. But there is a more fundamental doubt about his result. The whole method is based on the assumption that the intrinsic brightness of a galaxy remains constant. What if it changes with time? We are seeing the light of the distant galaxies as it was emitted at widely different times in the past - 500 million, a billion, two billion years ago. If the stars in the galaxies are burning out, the galaxies must dim as they grow older. A galaxy two billion light-years away cannot be put on the same distance scale with a galaxy 500 million light-years away unless we take into account the fact that we are seeing the nearer galaxy at an older, and less bright, age. The remote galaxy is farther away than a mere comparison of the luminosity of the two would suggest.
When a correction is made for the assumed decline in brightness with age, the more distant galaxies are spread out to farther distances than Hubble assumed. In fact, the calculations of volume are changed so drastically that we may have to reverse the conclusion about the curvature of space. We are not sure, because we do not yet know enough about the evolution of galaxies. But if we find that galaxies wane in intrinsic brightness by only a few per cent in a billion years, we shall have to conclude that space is curved negatively and the universe is infinite.
Actually there is another line of reasoning which supports the side of infinity. Our universe seems to be hyperbolic and ever-expanding. Mathematical solutions of fundamental cosmological equations indicate that such a universe is open and infinite.
We have reviewed the questions that dominated the thinking of cosmologists during the first half of this century: the conception of a four-dimensional space-time continuum, of curved space, of an expanding universe and of a cosmos that is either finite or infinite. Now we must consider the major present issue in cosmology: Is the universe in truth evolving, or is it in a steady state of equilibrium that has always existed and will go on through eternity? Most cosmologists take the evolutionary view. But in 1951 a group at the University of Cambridge, whose chief spokesman has been Fred Hoyle, advanced the steady-state idea. Essentially their theory is that the universe is infinite in space and time that it has neither a beginning nor an end, that the density of its matter remains constant, that new matter is steadily being created in space at a rate that exactly compensates for the thinning of matter by expansion, that as a consequence new galaxies are continually being born, and that the galaxies of the universe therefore range in age from mere youngsters to veterans of 5, 10, 20 and more billions of years. In my opinion this theory must be considered very questionable because of the simple fact (apart from other reasons) that the galaxies in our neighbourhood all seem to be of the same age as our own Milky Way. But the issue is many-sided and fundamental, and can be settled only by extended study of the universe as far as we can observe it . . . Thus coming to summarize the evolutionary theory.
We assume that the universe started from a very dense state of matter. In the early stages of its expansion, radiant energy was dominant over the mass of matter. We can measure energy and matter on a common scale by means of the well-known equation E=mc2, which says that the energy equivalent of matter is the mass of the matter multiplied by the square of the velocity of light. Energy can be translated into mass, conversely, by dividing the energy quantity by c2. Thus we can speak of the ‘mass density’ of energy. Now at the beginning the mass density of the radiant energy was incomparably greater than the density of the matter in the universe. But in an expanding system the density of radiant energy decreases faster than does the density of matter. The former thins out as the fourth power of the distance of expansion: as the radius of the system doubles, the density of radiant energy drops to one sixteenth. The density of matter declines as the third power; a doubling of the radius means an eightfold increase in volume, or eightfold decrease in density.
Assuming that the universe at the beginning was under absolute rule by radiant energy, we can calculate that the temperature of the universe was 250 million degrees when it was one hour old, dropped to 6,000 degrees (the present temperature of our sun's surface) when it was 200,000 years old and had fallen to about 100 degrees below the freezing point of water when the universe reached its 250-millionth birthday.
This particular birthday was a crucial one in the life of the universe. It was the point at which the density of ordinary matter became greater than the mass density of radiant energy, because of the more rapid fall of the latter. The switch from the reign of radiation to the reign of matter profoundly changed matter's behaviours. During the eons of its subjugation to the will of radiant energy (i.e., light), it must have been spread uniformly through space in the form of thin gas. But as soon as matter became gravitationally more important than the radiant energy, it began to acquire a more interesting character. James Jeans, in his classic studies of the physics of such a situation, proved half a century ago that a gravitating gas filling a very large volume is bound to break up into individual ‘gas balls’, the size of which is determined by the density and the temperature of the gas. Thus in the year 250,000,000 A. B. E. (after the beginning of expansion), when matter was freed from the dictatorship of radiant energy, the gas broke up into giant gas clouds, slowly drifting apart as the universe continued to expand. Applying Jeans's mathematical formula for the process to the gas filling the universe at that time, in that these primordial balls of gas would have had just about the mass that the galaxies of stars possess today. They were then only ‘proto galaxies’ - cold, dark and chaotic. But their gas soon condensed into stars and formed the galaxies as we see them now.
A central question in this picture of the evolutionary universe is the problem of accounting for the formation of the varied kinds of matter composing it, i.e., the chemical elements . . . Its belief is that at the start matter was composed simply of protons, neutrons and electrons. After five minutes the universe must have cooled enough to permit the aggregation of protons and neutrons into larger units, from deuterons (one neutron and one proton) up to the heaviest elements. This process must have ended after about 30 minutes, for by that time the temperature of the expanding universe must have dropped below the threshold of thermonuclear reactions among light elements, and the neutrons must have been used up in element-building or been converted to protons.
To many, the statement that the present chemical constitution of our universe was decided in half an hour five billion years ago will sound nonsensical. But consider a spot of ground on the atomic proving ground in Nevada where an atomic bomb was exploded three years ago. Within one microsecond the nuclear reactions generated by the bomb produced a variety of fission products. Today, 100 million-million microseconds later, the site is still "hot" with the surviving fission products. The ratio of one microsecond to three years is the same as the ratio of half an hour to five billion years! If we can accept a time ratio of this order in the one case, why not in the other?
The late Enrico Fermi and Anthony L. Turkevich at the Institute for Nuclear Studies of the University of Chicago undertook a detailed study of thermonuclear reactions such as must have taken place during the first half hour of the universe's expansion. They concluded that the reactions would have produced about equal amounts of hydrogen and helium, making up 99 per cent of the total material, and about 1 per cent of deuterium. We know that hydrogen and helium do in fact make up about 99 per cent of the matter of the universe. This leaves us with the problem of building the heavier elements. Hold to opinion, that some of them were built by capture of neutrons. However, since the absence of any stable nucleus of atomic weight 5 makes it improbable that the heavier elements could have been produced in the first half hour in the abundances now observed, and, yet agreeing that the lion's share of the heavy elements may have been formed later in the hot interiors of stars.
All the theories - of the origin, age, extent, composition and nature of the universe - are becoming more subject to test by new instruments and new techniques. . . . But we must not forget that the estimate of distances of the galaxies is still founded on the debatable assumption that the brightness of galaxies does not change with time. If galaxies actually diminish in brightness as they age, the calculations cannot be depended upon. Thus the question whether evolution is or is not taking place in the galaxies is of crucial importance at the present stage of our outlook on the universe.
In addition certain branches of physical science focus on energy and its large-scale effects. Thermodynamics is the study of heat and the effects of converting heat into other kinds of energy. This branch of physics has a host of highly practical applications because heat is often used to power machines. Physicists also investigate electrical energy and energy that are carried in electromagnetic waves. These include radio waves, light rays, and X rays - forms of energy that are closely related and that all obey the same set of rules. Chemistry is the study of the composition of matter and the way different substances interact - subjects that involve physics on an atomic scale. In physical chemistry, chemists study the way physical laws govern chemical change, while in other branches of chemistry the focus is on particular chemicals themselves. For example, inorganic chemistry investigates substances found in the nonliving world and organic chemistry investigates carbon-based substances. Until the 19th century, these two areas of chemistry were thought to be separate and distinct, but today chemists routinely produce organic chemicals from inorganic raw materials. Organic chemists have learned how to synthesize many substances that are found in nature, together with hundreds of thousands that are not, such as plastics and pesticides. Many organic compounds, such as reserpine, a drug used to treat hypertension, cost less to produce by synthesizing from inorganic raw materials than to isolate from natural sources. Many synthetic medicinal compounds can be modified to make them more effective than their natural counterparts, with fewer harmful side effects.
The branch of chemistry known as biochemistry deals solely with substances found in living things. It investigates the chemical reactions that organisms use to obtain energy and the reactions up which they use to build themselves. Increasingly, this field of chemistry has become concerned not simply with chemical reactions themselves but also with how the shape of molecules influences the way they work. The result is the new field of molecular biology, one of the fastest-growing sciences today.
Physical scientists also study matter elsewhere in the universe, including the planets and stars. Astronomy is the science of the heavens usually, while astrophysics is a branch of astronomy that investigates the physical and chemical nature of stars and other objects. Astronomy deals largely with the universe as it appears today, but a related science called cosmology looks back in time to answer the greatest scientific questions of all: how the universe began and how it came to be as it is today.
The earth sciences examine the structure and composition of our planet, and the physical processes that have helped to shape it. Geology focuses on the structure of Earth, while geography is the study of everything on the planet's surface, including the physical changes that humans have brought about from, for example, farming, mining, or deforestation. Scientists in the field of geomorphology study Earth's present landforms, while mineralogists investigate the minerals in Earth's crust and the way they formed. Water dominates Earth's surface, making it an important subject for scientific research. Oceanographers carry out research in the oceans. While scientists working in the field of hydrology investigate water resources on land, a subject of vital interest in areas prone to drought. Glaciologists study Earth's icecaps and mountain glaciers, and the effects that ice have when it forms, melts, or moves. In atmospheric science, meteorology deals with day-to-day changes in weather, but climatology investigates changes in weather patterns over the longer term.
When living things die their remains are sometimes preserved, creating a rich store of scientific information: Palaeontology is the study of plant and animal remains that have been preserved in sedimentary rock, often millions of years ago. Paleontologists study things long dead and their findings shed light on the history of evolution and on the origin and development of humans. A related science, called palynology, is the study of fossilized spores and pollen grains. Scientists study these tiny structures to learn the types of plants that grew in certain areas during Earth’s history, which also helps identify what Earth’s climates were like in the past.
The life sciences include all those areas of study that deal with living things. Biology is the general study of the origin, development, structure, function, evolution, and distribution of living things. Biology may be divided into botany, the study of plants; zoology, the study of animals; and microbiology, the study of the microscopic organisms, such as bacteria, viruses, and fungi. Many single-celled organisms play important roles in life processes and thus are important to more complex forms of life, including plants and animals.
Genetics is the branch of biology that studies the way in which characteristics are transmitted from an organism to its offspring. In the latter half of the 20th century, new advances made it easier to study and manipulate genes at the molecular level, enabling scientists to catalogue all the genes finds in each cell of the human body. Exobiology, a new and still speculative field, is the study of possible extraterrestrial life. Although Earth remains the only place known to support life, many believe that it is only a matter of time before scientists discover life elsewhere in the universe.
While exobiology is one of the newest life sciences, anatomy is one of the oldest. It is the study of plant and animal structures, carried out by dissection or by using powerful imaging techniques. Gross anatomy deals with structures that are large enough to see, while microscopic anatomy deals with much smaller structures, down to the level of individual cells.
Physiology explores how living things’ work. Physiologists study processes such as cellular respiration and muscle contraction, as well as the systems that keep these processes under control. Their work helps to answer questions about one of the key characteristics of life, the fact that most living things maintain a steady internal state when the environment around them constantly changes.
Together, anatomy and physiology form two of the most important disciplines in medicine, the science of treating injury and human disease. General medical practitioners have to be familiar with human biology as a whole, but medical science also includes a host of clinical specialties. They include sciences such as cardiology, urology, and oncology, which investigate particular organs and disorders, and pathology, the general study of disease and the changes that it causes in the human body.
As well as working with individual organisms, life scientists also investigate the way living things interact. The study of these interactions, known as ecology, has become a key area of study in the life sciences as scientists become increasingly concerned about the disrupting effects of human activities on the environment.
The social sciences explore human society past and present, and the way human beings behave. They include sociology, which investigates the way society is structured and how it functions, as well as psychology, which is the study of individual behaviour and the mind. Social psychology draws on research in both these fields. It examines the way society influence’s people's behaviour and attitudes.
Another social science, anthropology, looks at humans as a species and examines all the characteristics that make us what we are. These include not only how people relate to each other but also how they interact with the world around them, both now and in the past. As part of this work, anthropologists often carry out long-term studies of particular groups of people in different parts of the world. This kind of research helps to identify characteristics that all human beings share and those that are the products of local culture, learned and handed on from generation to generation.
The social sciences also include political science, law, and economics, which are products of human society. Although far removed from the world of the physical sciences, all these fields can be studied in a scientific way. Political science and law are uniquely human concepts, but economics has some surprisingly close parallels with ecology. This is because the laws that govern resource use, productivity, and efficiency do not operate only in the human world, with its stock markets and global corporations, but in the nonhuman world as well in technology, scientific knowledge is put to practical ends. This knowledge comes chiefly from mathematics and the physical sciences, and it is used in designing machinery, materials, and industrial processes. Overall, this work is known as engineering, a word dating back to the early days of the Industrial Revolution, when an ‘engine’ was any kind of machine.
Engineering has many branches, calling for a wide variety of different skills. For example, aeronautical engineers need expertise in the science of fluid flow, because aeroplanes fly through air, which is a fluid. Using wind tunnels and computer models, aeronautical engineers strive to minimize the air resistance generated by an aeroplane, while at the same time maintaining a sufficient amount of lift. Marine engineers also need detailed knowledge of how fluids behave, particularly when designing submarines that have to withstand extra stresses when they dive deep below the water’s surface. In civil engineering, stress calculations ensure that structures such as dams and office towers will not collapse, particularly if they are in earthquake zones. In computing, engineering takes two forms: hardware design and software design. Hardware design refers to the physical design of computer equipment (hardware). Software design is carried out by programmers who analyse complex operations, reducing them to a series of small steps written in a language recognized by computers.
In recent years, a completely new field of technology has developed from advances in the life sciences. Known as biotechnology, it involves such varied activities as genetic engineering, the manipulation of genetic material of cells or organisms, and cloning, the formation of genetically uniform cells, plants, or animals. Although still in its infancy, many scientists believe that biotechnology will play a major role in many fields, including food production, waste disposal, and medicine. Science exists because humans have a natural curiosity and an ability to organize and record things. Curiosity is a characteristic shown by many other animals, but organizing and recording knowledge is a skill demonstrated by humans alone.
During prehistoric times, humans recorded information in a rudimentary way. They made paintings on the walls of caves, and they also carved numerical records on bones or stones. They may also have used other ways of recording numerical figures, such as making knots in leather cords, but because these records were perishable, no traces of them remain. Even so, with the invention of writing about 6,000 years ago, a new and much more flexible system of recording knowledge appeared.
The earliest writers were the people of Mesopotamia, who lived in a part of present-day Iraq. Initially they used a pictographic script, inscribing tallies and lifelike symbols on tablets of clay. With the passage of time, these symbols gradually developed into cuneiform, a much more stylized script composed of wedge-shaped marks.
Because clay is durable, many of these ancient tablets still survive. They show that when writing first appeared. The Mesopotamians already had a basic knowledge of mathematics, astronomy, and chemistry, and that they used symptoms to identify common diseases. During the following 2,000 years, as Mesopotamian culture became increasingly sophisticated, mathematics in particular became a flourishing science. Knowledge accumulated rapidly, and by 1000 Bc the earliest private libraries had appeared.
Southwest of Mesopotamia, in the Nile Valley of northeastern Africa, the ancient Egyptians developed their own form of a pictographic script, writing on papyrus, or inscribing text in stone. Written records from 1500 Bc. shows that, like the Mesopotamians, the Egyptians had a detailed knowledge of diseases. They were also keen astronomers and skilled mathematicians - a fact demonstrated by the almost perfect symmetry of the pyramids and by other remarkable structures they built.
For the peoples of Mesopotamia and ancient Egypt, knowledge was recorded mainly for practical needs. For example, astronomical observations enabled the development of early calendars, which helped in organizing the farming year. Yet in ancient Greece, often recognized as the birthplace of Western science, a new slightly scientific enquiry began. Here, philosophers sought knowledge largely for its own sake.
Thales of Miletus were one of the first Greek philosophers to seek natural causes for natural phenomena. He travelled widely throughout Egypt and the Middle East and became famous for predicting a solar eclipse that occurred in 585 Bc. At a time when people regarded eclipses as ominous, inexplicable, and frightening events, his prediction marked the start of rationalism, a belief that the universe can be explained by reason alone. Rationalism remains the hallmark of science to this day.
Thales and his successors speculated about the nature of matter and of Earth itself. Thales himself believed that Earth was a flat disk floating on water, but the followers of Pythagoras, one of ancient Greece's most celebrated mathematicians, believed that Earth was spherical. These followers also thought that Earth moved in a circular orbit - not around the Sun but around a central fire. Although flawed and widely disputed, this bold suggestion marked an important development in scientific thought: the idea that Earth might not be, after all, the centre of the universe. At the other end of the spectrum of scientific thought, the Greek philosopher Leucippus and his student Democritus of Abdera proposed that all matter be made up of indivisible atoms, more than 2,000 years before the idea became a part of modern science.
As well as investigating natural phenomena, ancient Greek philosophers also studied the nature of reasoning. At the two great schools of Greek philosophy in Athens - the Academy, founded by Plato, and the Lyceum, founded by Plato's pupil Aristotle - students learned how to reason in a structured way using logic. The methods taught at these schools included induction, which involve taking particular cases and using them to draw general conclusions, and deduction, the process of correctly inferring new facts from something already known.
In the two centuries that followed Aristotle's death in 322 Bc, Greek philosophers made remarkable progress in a number of fields. By comparing the Sun's height above the horizon in two different places, the mathematician, astronomer, and geographer Eratosthenes calculated Earth's circumference, producing the figure of an accurate overlay within one percent. Another celebrated Greek mathematician, Archimedes, laid the foundations of mechanics. He also pioneered the science of hydrostatics, the study of the behaviour of fluids at rest. In the life sciences, Theophrastus founded the science of botany, providing detailed and vivid descriptions of a wide variety of plant species as well as investigating the germination process in seeds.
By the 1st century Bc, Roman power was growing and Greek influence had begun to wane. During this period, the Egyptian geographer and astronomer Ptolemy charted the known planets and stars, putting Earth firmly at the centre of the universe, and Galen, a physician of Greek origin, wrote important works on anatomy and physiology. Although skilled soldiers, lawyers, engineers, and administrators, the Romans had little interest in basic science. As a result, scientific growth made little advancement in the days of the Roman Empire. In Athens, the Lyceum and Academy were closed down in Ad 529, bringing the first flowering of rationalism to an end.
For more than nine centuries, from about ad 500 to 1400, Western Europe made only a minor contribution to scientific thought. European philosophers became preoccupied with alchemy, a secretive and mystical pseudoscience that held out the illusory promise of turning inferior metals into gold. Alchemy did lead to some discoveries, such as sulfuric acid, which was first described in the early 1300's, but elsewhere, particularly in China and the Arab world, much more significant progress in the sciences was made.
Chinese science developed in isolation from Europe, and followed a different pattern. Unlike the Greeks, who prized knowledge as an end, the Chinese excelled at turning scientific discoveries to practical ends. The list of their technological achievements is dazzling: it includes the compass, invented in about Ad. 270; wood-block printing, developed around 700, and gunpowder and movable type, both invented around the year 1000. The Chinese were also capable mathematicians and excellent astronomers. In mathematics, they calculated the value of π (pi) to within seven decimal places by the year 600, while in astronomy, one of their most celebrated observations was that of the supernova, or stellar explosion, that took place in the Crab Nebula in 1054. China was also the source of the world's oldest portable star map, dating from about 940 Bc.
The Islamic world, which in medieval times extended as far west as Spain, also produced many scientific breakthroughs. The Arab mathematician Muhammad al-Khwarizmi introduced Hindu-Arabic numerals to Europe many centuries after they had been devised in southern Asia. Unlike the numerals used by the Romans, Hindu-Arabic numerals include zero, a mathematical device unknown in Europe at the time. The value of Hindu-Arabic numerals depends on their place: in the number 300, for example, the numeral three is worth ten times as much as in 30. Al-Khwarizmi also wrote on algebra (it derived from the Arab word al-jabr), and his name survives in the word algorithm, a concept of great importance in modern computing.
In astronomy, Arab observers charted the heavens, giving many of the brightest stars the names we use today, such as Aldebaran, Altair, and Deneb. Arab scientists also explored chemistry, developing methods to manufacture metallic alloys and test the quality and purity of metals. As in mathematics and astronomy, Arab chemists left their mark in some of the names they used - alkali and alchemy, for example, are both words of Arabic origin. Arab scientists also played a part in developing physics. One of the most famous Egyptian physicists, Alhazen, published a book that dealt with the principles of lenses, mirrors, and other devices used in optics. In this work, he rejected the then-popular idea that eyes give out light rays. Instead, he correctly deduced that eyes work when light rays enter the eye from outside.
In Europe, historians often attribute the rebirth of science to a political event - the capture of Constantinople (now Istanbul) by the Turks in 1453. At the time, Constantinople was the capital of the Byzantine Empire and a major seat of learning. Its downfall led to an exodus of Greek scholars to the West. In the period that followed, many scientific works, including those originally from the Arab world, were translated into European languages. Through the invention of the movable type printing press by Johannes Gutenberg around 1450, copies of these texts became widely available.
The Black Death, a recurring outbreak of bubonic plague that began in 1347, disrupted the progress of science in Europe for more than two centuries. However, in 1543 two books were published that had a profound impact on scientific progress. One was De Corporis Humani Fabrica (On the Structure of the Human Body, 7 volumes, 1543), by the Belgian anatomist Andreas Vesalius. Vesalius studied anatomy in Italy, and his masterpiece, which was illustrated by superb woodcuts, corrected errors and misunderstandings about the body before which had persisted since the time of Galen more than 1,300 years. Unlike Islamic physicians, whose religion prohibited them from dissecting human cadavers, Vesalius investigated the human body in minute detail. As a result, he set new standards in anatomical science, creating a reference work of unique and lasting value.
The other book of great significance published in 1543 was De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres), written by the Polish astronomer . In it, Copernicus rejected the idea that Earth was the centre of the universe, as proposed by Ptolemy in the 1st century Bc. Instead, he set out to prove that Earth, together with the other planets, follows orbits around the Sun. Other astronomers opposed Copernicus's ideas, and more ominously, so did the Roman Catholic Church. In the early 1600's, the church placed the book on a list of forbidden works, where it remained for more than two centuries. Despite this ban and despite the book's inaccuracies (for instance, Copernicus believed that Earth's orbit was circular rather than elliptical), De Revolutionibus remained a momentous achievement. It also marked the start of a conflict between science and religion that has dogged Western thought ever since
In the first decade of the 17th century, the invention of the telescope provided independent evidence to support Copernicus's views. Italian physicist and astronomer Galileo Galilei used the new device to remarkable effect. He became the first person to observe satellites circling Jupiter, the first to make detailed drawings of the surface of the Moon, and the first to see how Venus waxes and wanes as it circles the Sun.
These observations of Venus helped to convince Galileo that Copernicus’s Sun-entered view of the universe had been correct, but he fully understood the danger of supporting such heretical ideas. His Dialogue on the Two Chief World Systems, Ptolemaic and Copernican, published in 1632, was carefully crafted to avoid controversy. Even so, he was summoned before the Inquisition (tribunal established by the pope for judging heretics) the following year and, under threat of torture, forced to recant.
Nicolaus Copernicus (1473-1543), the first developed heliocentric theory of the Universes in the modern era presented in De Revolutioniv bus Coelestium, published in the year of Copernicus’s death. The system is entirely mathematical, in the sense of predicting the observed position of celestial bodies on te basis of an underlying geometry, without exploring the mechanics of celestial motion. Its mathematical and scientific superiority over the Ptolemaic system was not as direct as poplar history suggests: Copernicus’s system adhered to circular planetary motion and let the planets run on 48 epicycles and eccentrics. It was not until the work of Kepler and Galileo that the system became markedly simpler than Ptolemaic astronomy.
The publication of Nicolaus Copernicus's De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in 1543 is traditionally considered the inauguration of the scientific revolution. Ironically, Copernicus had no intention of introducing radical ideas into cosmology. His aim was only to restore the purity of ancient Greek astronomy by eliminating novelties introduced by Ptolemy. And with such an aim in mind he modeled his own book, which would turn astronomy upside down, on Ptolemy's Almagest. At the core of the Copernican system, as with that of Aristarchus before him, is the concept of the stationary Sun at the center of the universe, and the revolution of the planets, Earth included, around the Sun. The Earth was ascribed, in addition to an annual revolution around the Sun, a daily rotation around its axis.
Copernicus's greatest achievement is his legacy. By introducing mathematical reasoning into cosmology, he dealt a severe blow to Aristotelian common-sense physics. His concept of an Earth in motion launched the notion of the Earth as a planet. And his explanation that he had been unable to detect stellar parallax because of the enormous distance of the sphere of the fixed stars opened the way for future speculation about an infinite universe. Nevertheless, Copernicus still clung to many traditional features of Aristotelian cosmology. He continued to advocate the entrenched view of the universe as a closed world and to see the motion of the planets as uniform and circular. Thus, in evaluating Copernicus's legacy, it should be noted that he set the stage for far more daring speculations than he himself could make. The heavy metaphysical underpinning of Kepler's laws, combined with an obscure style and a demanding mathematics, caused most contemporaries to ignore his discoveries. Even his Italian contemporary Galileo Galilei, who corresponded with Kepler and possessed his books, never referred to the three laws. Instead, Galileo provided the two important elements missing from Kepler's work: a new science of dynamics that could be employed in an explanation of planetary motion, and a staggering new body of astronomical observations. The observations were made possible by the invention of the telescope in Holland c.1608 and by Galileo's ability to improve on this instrument without ever having seen the original. Thus equipped, he turned his telescope skyward, and saw some spectacular sights.
The results of his discoveries were immediately published in the Sidereus nuncius (The Starry Messenger) of 1610. Galileo observed that the Moon was very similar to the Earth, with mountains, valleys, and oceans, and not at all that perfect, smooth spherical body it was claimed to be. He also discovered four moons orbiting Jupiter. As for the Milky Way, instead of being a stream of light, it was, rather, a large aggregate of stars. Later observations resulted in the discovery of sunspots, the phases of Venus, and that strange phenomenon which would later be designated as the rings of Saturn.
Having announced these sensational astronomical discoveries--which reinforced his conviction of the reality of the heliocentric theory--Galileo resumed his earlier studies of motion. He now attempted to construct a comprehensive new science of mechanics necessary in a Copernican world, and the results of his labors were published in Italian in two epoch-making books: Dialogue Concerning the Two Chief World Systems (1632) and Discourses and Mathematical Demonstrations Concerning the Two New Sciences (1638). His studies of projectiles and free-falling bodies brought him very close to the full formulation of the laws of inertia and acceleration (the first two laws of Isaac Newton). Galileo's legacy includes both the modern notion of "laws of nature" and the idea of mathematics as nature's true language. He contributed to the mathematization of nature and the geometrization of space, as well as to the mechanical philosophy that would dominate the 17th and 18th centuries. Perhaps most important, it is largely due to Galileo that experiments and observations serve as the cornerstone of scientific reasoning.
Today, Galileo is remembered equally well because of his conflict with the Roman Catholic church. His uncompromising advocacy of Copernicanism after 1610 was responsible, in part, for the placement of Copernicus's De revolutionibus on the Index of Forbidden Books in 1616. At the same time, Galileo was warned not to teach or defend Copernicanism in public. The election of Galileo's friend Maffeo Barberini as Pope Urban VIII in 1624 filled Galileo with the hope that such a verdict could be revoked. With perhaps some unwarranted optimism, Galileo set to work to complete his Dialogue (1632). However, Galileo underestimated the power of the enemies he had made during the previous two decades, particularly some Jesuits who had been the target of his acerbic tongue. The outcome was that Galileo was summoned to Rome and there forced to abjure, on his knees, the views he had expressed in his book. Ever since, Galileo has been portrayed as a victim of a repressive church and a martyr in the cause of freedom of thought; as such, he has become a powerful symbol.
Despite his passionate advocacy of Copernicanism and his fundamental work in mechanics, Galileo continued to accept the age-old views that planetary orbits were circular and the cosmos an enclosed world. These beliefs, as well as a reluctance rigorously to apply mathematics to astronomy as he had previously applied it to terrestrial mechanics, prevented him from arriving at the correct law of inertia. Thus, it remained for Isaac Newton to unite heaven and Earth in his immense intellectual achievement, the Philosophiae naturalis principia mathematica (Mathematical Principles of Natural Philosophy), which was published in 1687. The first book of the Principia contained Newton's three laws of motion. The first expounds the law of inertia: every body persists in a state of rest or uniform motion in a straight line unless compelled to change such a state by an impressing force. The second is the law of acceleration, according to which the change of motion of a body is proportional to the force acting upon it and takes place in the direction of the straight line along which that force is impressed. The third, and most original, law ascribes to every action an opposite and equal reaction. These laws governing terrestrial motion were extended to include celestial motion in book 3 of the Principia, where Newton formulated his most famous law, the law of gravitation: every body in the universe attracts any other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
The Principia is deservedly considered one of the greatest scientific masterpieces of all time. But in 1704, Newton published his second great work, the Opticks, in which he formulated his corpuscular theory of light and his theory of colors. In later editions Newton appended a series of "queries" concerning various related topics in natural philosophy. These speculative, and sometimes metaphysical, statements on such issues as light, heat, ether, and matter became most productive during the 18th century, when the book and the experimental method it propagated became immensely popular.
The impact of the Newtonian accomplishment was enormous. Newton's two great books resulted in the establishment of two traditions that, though often mutually exclusive, nevertheless permeated into every area of science. The first was the mathematical and reductionist tradition of the Principia, which, like René Descartes's mechanical philosophy, propagated a rational, well-regulated image of the universe. The second was the experimental tradition of the Opticks, somewhat less demanding than the mathematical tradition and, owing to the speculative and suggestive queries appended to the Opticks, highly applicable to chemistry , biology, and the other new scientific disciplines that began to flourish in the 18th century. This is not to imply that everyone in the scientific establishment was, or would be, a Newtonian. Newtonianism had its share of detractors. Rather, the Newtonian achievement was so great, and its applicability to other disciplines so strong, that although Newtonian science could be argued against, it could not be ignored. In fact, in the physical sciences an initial reaction against universal gravitation occurred. For many, the concept of action at a distance seemed to hark back to those occult qualities which the mechanical philosophy of the 17th century had done away with. By the second half of the 18th century, however, universal gravitation would be proved correct, thanks to the work of Leonhard Euler, A. C. Clairaut, and Pierre Simon de LaPlace, the last of whom announced the stability of the solar system in his masterpiece Celestial Mechanics (1799-1825).
Newton's influence was not confined to the domain of the natural sciences. The philosophes of the 18th-century Enlightenment sought to apply scientific methods to the study of human society. To them, the empiricist philosopher John Locke was the first person to attempt this. They believed that in his Essay on Human Understanding (1690) Locke did for the human mind what Newton had done for the physical world. Although Locke's psychology and epistemology were to come under increasing attack as the 18th century advanced, other thinkers such as Adam Smith, David Hume, and Abbé de Condillac would aspire to become the Newtons of the mind or the moral realm. These confident, optimistic men of the Enlightenment argued that there must exist universal human laws that transcend differences of human behaviour and the variety of social and cultural institutions. Labouring under such an assumption, they sought to uncover these laws and apply them to the new society they hoped to bring about.
As the 18th century progressed, the optimism of the philosophes waned and a reaction began to set in. Its first manifestation occurred in the religious realm. The mechanistic interpretation of the world--shared by Newton and Descartes--had, in the hands of the philosophes, led to materialism and atheism. Thus, by mid-century the stage was set for a revivalist movement, which took the form of Methodism in England and pietism in Germany. By the end of the century the romantic reaction had begun (see romanticism). Fueled in part by religious revivalism, the romantics attacked the extreme rationalism of the Enlightenment, the impersonalization of the mechanistic universe, and the contemptuous attitude of "mathematicians" toward imagination, emotions, and religion.
The romantic reaction, however, was not antiscientific; its adherents rejected a specific type of the mathematical sciences, not the entire enterprise. In fact, the romantic reaction, particularly in Germany, would give rise to a creative movement--the Naturphilosophie--that in turn would be crucial for the development of the biological and life sciences in the 19th century, and would nourish the metaphysical foundation necessary for the emergence of the concepts of energy, forces, and conservation
Thus and so, in classical physics, external reality consisted of inert and inanimate matter moving in accordance with wholly deterministic natural laws, and collections of discrete atomized parts constituted wholes. Classical physics was also premised, however, on a dualistic conception of reality as consisting of abstract disembodied ideas existing in a domain separate from and superior to sensible objects and movements. The motion that the material world experienced by the senses was inferior to the immaterial world experiences by mind or spirit has been blamed for frustrating the progress of physics up too at least the time of Galileo. Nevertheless, in one very important respect it also made the fist scientific revolution possible. Copernicus, Galileo, Kepler and Newton firmly believed that the immaterial geometrical mathematical ides that inform physical reality had a prior existence in the mind of God and that doing physics was a form of communion with these ideas.
Even though instruction at Cambridge was still dominated by the philosophy of Aristotle, some freedom of study was permitted in the student's third year. Newton immersed himself in the new mechanical philosophy of Descartes, Gassendi, and Boyle; in the new algebra and analytical geometry of Vieta, Descartes, and Wallis; and in the mechanics and Copernican astronomy of Galileo. At this stage Newton showed no great talent. His scientific genius emerged suddenly when the plague closed the University in the summer of 1665 and he had to return to Lincolnshire. There, within 18 months he began revolutionary advances in mathematics, optics, physics, and astronomy.
During the plague years Newton laid the foundation for elementary differential and integral CALCULUS, several years before its independent discovery by the German philosopher and mathematician LEIBNIZ. The "method of fluxions," as he termed it, was based on his crucial insight that the integration of a function (or finding the area under its curve) is merely the inverse procedure to differentiating it (or finding the slope of the curve at any point). Taking differentiation as the basic operation, Newton produced simple analytical methods that unified a host of disparate techniques previously developed on a piecemeal basis to deal with such problems as finding areas, tangents, the lengths of curves, and their maxima and minima. Even though Newton could not fully justify his methods--rigorous logical foundations for the calculus were not developed until the 19th century--he receives the credit for developing a powerful tool of problem solving and analysis in pure mathematics and physics. Isaac Barrow, a Fellow of Trinity College and Lucasian Professor of Mathematics in the University, was so impressed by Newton's achievement that when he resigned his chair in 1669 to devote himself to theology, he recommended that the 27-year-old Newton take his place.
Newton's initial lectures as Lucasian Professor dealt with optics, including his remarkable discoveries made during the plague years. He had reached the revolutionary conclusion that white light is not a simple, homogeneous entity, as natural philosophers since Aristotle had believed. When he passed a thin beam of sunlight through a glass prism, he noted the oblong spectrum of colours--red, yellow, green, blue, violet--that formed on the wall opposite. Newton showed that the spectrum was too long to be explained by the accepted theory of the bending (or refraction) of light by dense media. The old theory said that all rays of white light striking the prism at the same angle would be equally refracted. Newton argued that white light is really a mixture of many different types of rays, that the different types of rays are refracted at slightly different angles, and that each different type of ray is responsible for producing a given spectral colour. A so-called crucial experiment confirmed the theory. Newton selected out of the spectrum a narrow band of light of one color. He sent it through a second prism and observed that no further elongation occurred. All the selected rays of one colour were refracted at the same angle.
These discoveries led Newton to the logical, but erroneous, conclusion that telescopes using refracting lenses could never overcome the distortions of chromatic dispersion. He therefore proposed and constructed a reflecting telescope, the first of its kind, and the prototype of the largest modern optical telescopes. In 1671 he donated an improved version to the Royal Society of London, the foremost scientific society of the day. As a consequence, he was elected a fellow of the society in 1672. Later that year Newton published his first scientific paper in the Philosophical Transactions of the society. It dealt with the new theory of light and color and is one of the earliest examples of the short research paper.
Newton's paper was well received, but two leading natural philosophers, Robert HOOKE and Christian HUYGENS, rejected Newton's naive claim that his theory was simply derived with certainty from experiments. In particular they objected to what they took to be Newton's attempt to prove by experiment alone that light consists in the motion of small particles, or corpuscles, rather than in the transmission of waves or pulses, as they both believed. Although Newton's subsequent denial of the use of hypotheses was not convincing, his ideas about scientific method won universal assent, along with his corpuscular theory, which reigned until the wave theory was revived in the early 19th century.
The debate soured Newton's relations with Hooke. Newton withdrew from public scientific discussion for about a decade after 1675, devoting himself to chemical and alchemical researches. He delayed the publication of a full account of his optical researches until after the death of Hooke in 1703. Newton's Opticks appeared the following year. It dealt with the theory of light and color and with Newton's investigations of the colors of thin sheets, of "Newton's rings," and of the phenomenon of diffraction of light. To explain some of his observations he had to graft elements of a wave theory of light onto his basically corpuscular theory. q
Newton's greatest achievement was his work in physics and celestial mechanics, which culminated in the theory of universal gravitation. Even though Newton also began this research in the plague years, the story that he discovered universal gravitation in 1666 while watching an apple fall from a tree in his garden is a myth. By 1666, Newton had formulated early versions of his three LAWS OF MOTION. He had also discovered the law stating the centrifugal force (or force away from the center) of a body moving uniformly in a circular path. However, he still believed that the earth's gravity and the motions of the planets might be caused by the action of whirlpools, or vortices, of small corpuscles, as Descartes had claimed. Moreover, although he knew the law of centrifugal force, he did not have a correct understanding of the mechanics of circular motion. He thought of circular motion as the result of a balance between two forces--one centrifugal, the other centripetal (toward the centre) - than as the result of one force, a centripetal force, which constantly deflects the body away from its inertial path in a straight line.
Newton's great insight of 1666 was to imagine that the Earth's gravity extended to the Moon, counterbalancing its centrifugal force. From his law of centrifugal force and Kepler's third law of planetary motion, Newton deduced that the centrifugal (and hence centripetal) force of the Moon or of any planet must decrease as the inverse square of its distance from the center of its motion. For example, if the distance is doubled, the force becomes one-fourth as much; if distance is trebled, the force becomes one-ninth as much. This theory agreed with Newton's data to within about 11%.
In 1679, Newton returned to his study of celestial mechanics when his adversary Hooke drew him into a discussion of the problem of orbital motion. Hooke is credited with suggesting to Newton that circular motion arises from the centripetal deflection of inertially moving bodies. Hooke further conjectured that since the planets move in ellipses with the Sun at one focus (Kepler's first law), the centripetal force drawing them to the Sun should vary as the inverse square of their distances from it. Hooke could not prove this theory mathematically, although he boasted that he could. Not to be shown up by his rival, Newton applied his mathematical talents to proving Hooke's conjecture. He showed that if a body obeys Kepler's second law (which states that the line joining a planet to the sun sweeps out equal areas in equal times), then the body is being acted upon by a centripetal force. This discovery revealed for the first time the physical significance of Kepler's second law. Given this discovery, Newton succeeded in showing that a body moving in an elliptical path and attracted to one focus must indeed be drawn by a force that varies as the inverse square of the distance. Later even these results were set aside by Newton.
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