HUMAN EVOLUTION

evolution of modern human beings from nonhuman and extinct hominid forms. The main stages of hominid evolution are represented by the australopithecines, Homo habilis, Homo erectus, and Homo sapiens. Human beings, extant and extinct, comprise the zoological family Hominidae; and the single living human species, Homo sapiens, is one of some 200 species of the order Primates, in turn one of 20 orders constituting the vertebrate class Mammalia. Among the past and present diversity of primates, hominids have long been recognized as having the closest resemblances, and hence affinities, to the African great apes (pongids); thus, in 1863 the British biologist T.H. Huxley noted in The Evidence as to Man's Place in Nature that whatever system of organs be studied . . . the structural differences which separate Man from the Gorilla and the Chimpanzee are not so great as those which separate the Gorilla from the lower apes . Various methods for the comparative evaluation of genetic character states have both repeatedly confirmed and measured in some detail the very close proximity of the extant African apes and modern Homo sapiens. All such findings are congruent with a common origin of apes and Hominidae, within the African continent, which took place some five to six million years ago. Three major areas are generally recognized within the subject of human evolution: primatology, which has as its major focus the biological and behavioral aspects of nonhuman primates; human paleontology, which is concerned with the recovery, description, and evaluation of the fossil evidence for hominid evolution; and paleoanthropology, which encompasses interrelated investigations into the biological and behavioral evolution of Hominidae. In addition, five major areas of research can be identified in human evolutionary studies: the origins of Hominidae, adaptation and diversification of the genus Australopithecus, the origins of the genus Homo, the emergence of Homo erectus and subsequent hominid occupation of Eurasia, and the origins and dispersals of premodern and modern Homo sapiens. Investigations of hominid origins are variously concerned with diverse comparative studies of extant higher primates and humans, as well as the search for ancestors in the fossil record. Pongids and hominids show a diversity of contrasting adaptations that evidently reflect their evolutionary divergences and which thus require explanation. Moreover, although markedly different from the Asian pongid (orangutan), the African pongids (gorilla and chimpanzee) differ from one another both structurally and behaviorally. The roots of Hominidae have been traced to at least four million years ago, and possibly to some five million years ago. The rarity and fragmentary condition of the few oldest known specimens, however, do not reveal critical aspects of hominid adaptation, such as modifications in trunk and lower-limb structure. Hence, the details of hominid origins remain unknown and the subject of lively debate and substantial speculation. The ancestral stock of extant African apes and of hominids also remains unknown, in large part a reflection of the paucity of fossil-bearing localities in the five- to 10-million-year time span. In the absence of a fossil record, structural and other adaptations have been projected back as an ancestral condition from living descendant species; but this is a very risky procedure that dismisses morphological transformation and adaptation and assumes stasis without complementary confirmation. The oldest definitely known hominids are attributed to the extinct genus Australopithecus. The genus speciated substantially, producing distinct and, in some cases, possibly convergent lineages. At least four species (afarensis, africanus, robustus, boisei) are commonly accepted, and two more (aethiopicus, crassidens) are recognized by some workers on morphological grounds. All species of the genus originated in the Pliocene epoch (5.3 to 1.6 million years ago), and the genus apparently became extinct in the Early Pleistocene (about 1.6 million to 900,000 years ago); its distribution is unknown outside the African continent. The oldest and most primitive species is A. afarensis, and most workers believe it to be ancestral to succedent species. Although they exhibited some fundamental hominid adaptations (bipedalism, reduction of anterior dentition, exploitation of nonforested habitats), most or all australopithecine species remained primitive in terms of growth and maturation, brain size and proportions, dietary adjustments, and complexity of cultural behaviour. Homo coexisted with the later, so-called robust, australopithecinesrobustus (and possibly crassidens) in southern Africa and boisei in East Africaalthough the adaptations enabling such coexistence are scarcely understood, and it is generally thought that an australopithecine species was ancestral to Homo. The recognition and suitable definition of the genus Homo and its initial representatives has been a persistently troublesome problem. There have been no formal diagnoses, and the few characterizations offered suffer from both lack of definitive character states and inclusiveness. The problem has been exacerbated as the hominid fossil record has expanded, particularly in respect to specimens dated to the end of the Pliocene epoch that lack distinctively Australopithecus-like characteristics. The first such specimens, found in the early 1960s in the Olduvai Gorge of Tanzania, were designated Homo habilis. Further remains of both comparable and greater age were subsequently recovered from northern Kenya and southwestern Ethiopia. Although a single initial Homo species (H. habilis) was originally proposed, this perspective has been criticized by some workers as simplistic because of the substantial variability of the fossil finds; accordingly, it is entirely possible that two contemporaneous and even sympatric species may have existed in the Late Pliocene. Coincident with the appearance and subsequent presence of such hominid(s) are various traces of associated culturally patterned behaviours. These include evidence of natural but transported and accumulated stone, flaked-stone artifacts, and occasional associated mammal (and other) skeletal parts, all of which indicate the exploitation and utilization of animal resources; the repeated utilization and occupation of particular locales; and the expanded employment of natural resources in conjunction with technological capabilities and requirements. Such biological and behavioral adaptations are believed by many workers to reflect major transformations and reorganizations in hominid phylogeny, perhaps consequent upon the initial appearance of genus Homo. The fossil record in sub-Saharan Africa affords evidence of the appearance of another, more derived (i.e., more evolved) species of HomoHomo erectusat the beginning of the Pleistocene epoch. At several localities in East and southern Africa, the species occurs sympatrically with the robust australopithecines. Less ancient occurrences are also known from northwestern Africa. The initial occupation of Eurasia by hominids appears to postdate such an antiquity, and it is generally inferred that the first Eurasian hominids were dispersals from an African source, perhaps between 1.5 and one million years ago. Homo erectus was first and, for a long time, best known from fossil finds in Southeast and East Asia. The fossil occurrences there range in age from approximately 1.6 million to 250,000 years. Although initial hominid occupation in Europe was probably at least as early, no human skeletal remains are known from the most ancient times, and those that have been founddated to between 500,000 and 300,000 years agodo not represent H. erectus but rather a form of H. sapiens that has been labeled archaic. The initial and subsequent penetration of hominids from the lower to middle latitudes occurred as the amplitude and intensity of glacialinterglacial climatic cycles was increasing. The extent to which there were attendant, and perhaps correlative, changes in human biology and in behaviour have remained the subjects of substantial research and much controversy. Traditionally, the tendency among students of hominid evolution was to attribute premodern human fossil finds to one or more extinct species, and sometimes even distinct genera, but as efforts increasingly have been directed at seeking congruence between developments in evolutionary biology and in the state of the hominid fossil record, substantial revisions in the classification of Hominidae have emerged. A variety of premodern human finds of both late Middle Pleistocene and early Late Pleistocene ages came to be subsumed within the species H. sapiens and were only further distinguished below the species level. This varied and increasingly large sample of post-erectus hominids came to be regarded as archaic H. sapiens, as distinguished from anatomically modern humans. This is largely a consequence of the mosaic of morphological features represented in the substantial variations among such materials, which exhibit primitive versus advanced, or derived, features. If early African H. erectus constituted the source of subsequent hominids, then it would appear that evolution proceeded quite differently in major geographic areas. For example, H. erectus is characteristic of the Asian Middle Pleistocene, where it is also long persistent and distinguished by its own group of singular, derived features. In Africa derivatives of early H. erectus are known, as are some transitional examples linking H. erectus to archaic H. sapiens. Skeletal parts of the earliest hominid occupants of western Eurasia are not known. The first examples from this area occur well into the Middle Pleistocene, and there is a range of variation in the specimens from strongly and partially erectus-like to incipiently Neanderthal-like, passing ultimately into the well-known and widely distributed Neanderthal peoples. The Neanderthals were for many years treated as a distinct species (Homo neanderthalensis), but they were subsequently subsumed as an archaic subspecies of H. sapiens. An increasingly substantial body of evidence has been accumulated, however, which suggests that a return to the older position is probably warranted. In western Europe, at least, there is increasing evidence of the contemporaneity of the last Neanderthal peoples with those early modern populations that have come to be known as Cro-Magnons. For these reasons, and in order to recognize and express differing degrees of derivation, further taxonomic evaluation and distinction of these archaic H. sapiens specimens is required, which will doubtless include the recognition of additional subspecies of both the H. erectus and H. neanderthalensis groups in western Eurasia and also corresponding taxonomic reassessment of various African Middle Pleistocene samples. In East Asia the existence and morphology of archaic H. sapiens has been well established, but the extent to which this form was a contemporaneous or a succedent replacement for the late H. erectus populations has not been firmly resolved. The roots of anatomically modern humans have long been a puzzle to students of human evolution and hence the source of much speculation and debate. Nonetheless, several developments have caused renewed interest in the problem from different perspectives. First, there has been the recognition of substantially greater relative and absolute ages for the archaeological industries of the African Middle Stone Age (about 200,000 to 40,000 years ago) and, correspondingly, some associated modernlike human skeletal parts. A series of such sub-Saharan occurrences has been identified within earlier and later segments of this time span. Second, there has been the recognition and broad acceptance of early modern human (often called Cro-Magnoid) populations in western Asia that were distinct from, and considerably older than (i.e., 90,000100,000 years ago), the known Neanderthals from that area and also much older than the European Cro-Magnon peoples who were widespread in Europe by some 30,00035,000 years ago. Third, there has been the increasing availability of comparative genetic data on degrees of affinities of modern human populations. The biochemical systems of Asian and European populations appear to be more similar to each other than those of either group are to African populations; thus, Asians and Europeans may have shared a common ancestry some 40,000 years ago and a common ancestry with African populations almost three times as long ago. Moreover, investigations of human mitochondrial DNA reveal two facts: that the variation among modern human populations is small compared, for example, with that between apes and monkeys, which points to the recency of human origin; and that there is a distinction between African and other human mitochondrial DNA types, suggesting the substantial antiquity of the African peoples and the relative recency of other human populations. F. Clark Howell The major focus of this article is on the physical evidenceboth fossil and lithicfor human evolution and on the interpretation of this evidence. For a detailed discussion of evolutionary theory, see evolution; for a detailed discussion of the evolution of human behaviour and culture, see stone age; Middle East, ancient; and prehistoric religion. the evolution of modern human beings from nonhuman and extinct hominid forms. The main stages of hominid evolution are represented by the australopithecines, Homo habilis, Homo erectus, and Homo sapiens; the last-named is the only living species of human being. The extant and extinct hominid forms constitute the family Hominidae, in the order Primates (class Mammalia). Modern primates comprise a remarkable gradational series culminating in the great apes and in humans. Humans and apes resemble each other in many anatomical features, including their skeletons and skulls, internal organs, musculature, dentition, sensory mechanisms, and brain structure. Genetic evidence points to an evolutionary divergence between the lineages of great apes and humans on the African continent between 10 and perhaps 6 million years ago. The oldest known hominid remains are classified as belonging to the genus Australopithecus and are found only in Africa. The species A. afarensis lived from about 4 to 3 million years ago. Standing about 100150 cm (3.55 feet) tall, A. afarensis combined an upright stance and bipedal locomotion with apelike features, including a forward-thrusting jaw and a brain that was only slightly larger (about 400500 cubic cm) than that of a modern chimpanzee. It is thought that A. afarensis is ancestral to the rather similar species A. africanus; two other species, A. (or Paranthropus) robustus and A. (or P.) boisei, also had appeared by 2 million years ago, but both are regarded as evolutionary dead ends. It is not clear whether A. afarensis or A. africanus gave rise to Homo habilis. Homo habilis appeared at least 2 million years ago and differed from Australopithecus in being slightly taller, having a larger cranial capacity (500 to 800 cubic cm), having more humanlike teeth, and having hands capable of the precise manipulation of objects. Homo habilis was distinguished above all by the ability to deliberately shape stones for use as tools, a capability that gives the species its name (Handy Man) and implies sufficient intelligence to justify its taxonomic designation as the first species of the genus Homo. Homo habilis inhabited sub-Saharan Africa until about 1.5 million years ago. A new, taller, and more human species, H. erectus, appears to have evolved from and supplanted H. habilis. This species lived from almost 2,000,000 to 250,000 years ago and gradually migrated into Asia and probably into parts of Europe. Homo erectus had a larger brain capacity (roughly 900 to 1,000 cubic cm) but also retained a number of apelike traits, including thick skull bones, jutting brow ridges, a receding forehead, and a projecting jaw. Nonetheless, H. erectus was recognizably human and apparently was the first hominid to master fire and to live in caves. Homo sapiens are thought to have first appeared about 400,000 years ago, certainly in Africa and perhaps in parts of Asia as well. The features of early-archaic H. sapiens more closely resembled those of H. erectus, but late-archaic forms had such modern human features as a brain capacity of about 1,350 cubic cm, a vertical forehead, rounded back part of the head, reduced jaws and teeth, clearly defined chin, and a fully erect posture and gait. Homo sapiens used hand axes and flake tools of increasingly greater variety and specificity. The human populations called Neanderthals, classified either as a separate species (H. neanderthalensis) or as a subspecies (H. sapiens neanderthalensis), inhabited Europe and the Mediterranean lands from about 200,000 years ago until they disappeared some 50,000 to 30,000 years ago. Anatomically modern humans appeared in Africa and possibly in Asia perhaps 100,000 years ago and eventually arrived in Europe. Whether they supplanted or absorbed Neanderthal populations is not clear. Among these European peoples, the best known are the Cro-Magnons. Their populations expanded rapidly throughout Europe, and their level of material culture became increasingly more complex and sophisticated. The emergence of fully modern humans in other parts of the world is less understood, though it seems to have occurred 30,00015,000 years ago and involved various migrations and the intermingling of different populations. Additional reading General works Charles Darwin, The Descent of Man and Selection in Relation to Sex, 2 vol. (1871), is historically the foundation reference. Edward O. Wilson, Sociobiology: The New Synthesis (1975); G.E. Kennedy, Paleoanthropology (1980); and Milford H. Wolpoff, Paleoanthropology (1980), are comprehensive general books.Overviews of human evolution include John Buettner-Janusch, Origins of Man: Physical Anthropology (1966); J.R. Napier, The Roots of Mankind (1970); W.E. Le Gros Clark, The Fossil Evidence for Human Evolution, 3rd ed. rev. and enlarged by Bernard G. Campbell (1978); Bernard Wood, Human Evolution (1978); Richard E. Leakey, The Making of Mankind (1981); C.B. Stringer (ed.), Aspects of Human Evolution (1981); Bernard G. Campbell, Human Evolution: An Introduction to Man's Adaptations, 3rd ed. (1985); Roger Lewin, In the Age of Mankind: A Smithsonian Book of Human Evolution (1988), and Human Evolution: An Illustrated Introduction, 2nd ed. (1989); D.R. Pilbeam, Human Evolution, Part I of G.A. Harrison et al., Human Biology: An Introduction to Human Evolution, Variation, Growth, and Adaptability, 3rd ed. (1988), pp. 1143; John Reader, Missing Links: The Hunt for Earliest Man, 2nd ed. (1988); Paul Mellars, Major Issues in the Emergence of Modern Humans, Current Anthropology, 30(3):349385 (June 1989); and Frank E. Poirier, Understanding Human Evolution, 2nd ed. (1990).Ian Tattersall, Eric Delson, and John Van Couvering (eds.), Encyclopedia of Human Evolution and Prehistory (1988), is detailed and comprehensive and includes up-to-date bibliographies. A detailed, authoritative, and highly useful catalog of fossil finds is Michael H. Day, Guide to Fossil Man, 4th ed. (1986). Meave G. Leakey and Richard E. Leakey (eds.), The Fossil Hominids and an Introduction to Their Context, 19681974 (1978), includes a lengthy catalog of the hominid finds at Koobi Fora. Michael R. Zimmerman and J. Lawrence Angel (eds.), Dating and Age Determination of Biological Materials (1986), includes discussion of dating human fossil remains. Two dated but still useful works are Phillip V. Tobias, The Brain in Hominid Evolution (1971), which contains data on endocranial capacity; and Kenneth P. Oakley, Man the Tool-Maker, 6th ed. (1972), an account of toolmaking development. Peter J. Bowler, Theories of Human Evolution: A Century of Debate, 18441944 (1986); and Roger Lewin, Bones of Contention (1987), discuss some of the major controversies in the field of paleoanthropology.Good accounts of modern and fossil primates are found in J.R. Napier and P.H. Napier, A Handbook of Living Primates: Morphology, Ecology, and Behaviour of Nonhuman Primates (1967); W.E. Le Gros Clark, The Antecedents of Man: An Introduction to the Evolution of the Primates, 3rd ed. (1971); Elwyn L. Simons, Primate Evolution: An Introduction to Man's Place in Nature (1972); Alison Jolly, The Evolution of Primate Behavior, 2nd ed. (1985); Daris R. Swindler and J. Erwin (eds.), Comparative Primate Biology, vol. 1, Systematics, Evolution, and Anatomy (1986); and John G. Fleagle, Primate Adaptation & Evolution (1988). F. Clark Howell Michael H. Day Australopithecus Donald C. Johanson and Maitland A. Edey, Lucy: The Beginnings of Humankind (1981), is a popular account of the discovery and interpretation of the Hadar hominids; and M.D. Leakey and J.M. Harris (eds.), Laetoli: A Pliocene Site in Northern Tanzania (1987), chronicles in detail the finds at this locality, including the tracks of hominid footprints. J.T. Robinson, Early Hominid Posture and Locomotion (1972), is also useful. Frederick E. Grine, The Evolutionary History of the Robust Australopithecines (1989), is a comprehensive and specialized guide on the opinions about australopithecine variation. Bernard Wood Homo habilis F.C. Howell, Hominidae, in Vincent J. Maglio and H.B.S. Cooke (eds.), Evolution of African Mammals (1978), pp. 154248, provides thorough descriptions of the fossils assigned to Homo habilis, in addition to information about Australopithecus. Richard Potts, Early Hominid Activities at Olduvai (1988), comments critically on hunting, scavenging, and social behaviour of the earliest humans, using the Olduvai archaeological evidence as a guide. P.V. Tobias, The Brain of Homo habilis: A New Level of Organization in Cerebral Evolution, Journal of Human Evolution, 16(78):741762 (1987), discusses the implications of brain anatomy for the use of language by the first representatives of Homo. C.B. Stringer, The Credibility of Homo habilis, in Bernard Wood, Lawrence Martin, and Peter Andrews (eds.), Major Topics in Primate and Human Evolution (1986), pp. 266294, advances the argument that fossils referred to as Homo habilis may actually document the presence of two distinct species in East Africa at about the same time. Homo erectus William W. Howells, Homo erectusWho, When, and Where: A Survey, Yearbook of Physical Anthropology, 23:123 (1980), is an excellent review. Lars-Knig Knigsson (ed.), Current Argument on Early Man (1980), contains proceedings from a Nobel symposium that includes several papers on H. erectus. Becky A. Sigmon and Jerome S. Cybulski (eds.), Homo erectus (1981), is a volume of essays by several authors who address history as well as current research on mid-Pleistocene humans. Useful works include Rukang Wu and Shenglong Lin, Peking Man, Scientific American, 248(6):8694 (June 1983), an account of excavations at Chou-k'ou-tien (Zhoukoudian), with information about the stone culture and hunting activities of Chinese Homo erectus; Peter Andrews and Jens Lorenz Franzen (eds.), The Early Evolution of Man, with Special Emphasis on Southeast Asia and Africa (1984), containing articles providing geologic background to the study of Homo erectus and discussion of anatomic features useful for defining the species; and G.P. Rightmire, Homo erectus and Later Middle Pleistocene Humans, Annual Review of Anthropology, 17:239260 (1988), a review emphasizing problems in the interpretation of the Middle Pleistocene fossil evidence. G. Philip Rightmire Homo sapiens General works Seymour W. Itzkoff, Triumph of the Intelligent: The Creation of Homo sapiens sapiens (1985), surveys the development of human intelligence and includes references to many classics in the field. Fred H. Smith and Frank Spencer (eds.), The Origins of Modern Humans: A World Survey of the Fossil Evidence (1984), provides regional discussions of late archaic humans and the emergence of modern humans, with emphasis on the ancestordescendant relationships between the regional groups. Cameron D. Ovey (ed.), The Swanscombe Skull: A Survey of Research on a Pleistocene Site (1964), brings together the information that is available concerning this fossil and its morphology, classification, dating, and site context. Michael H. Day Neanderthals Erik Trinkaus, The Neandertals and Modern Human Origins, Annual Review of Anthropology, 15:193218 (1986), provides an overview of behavioral contrasts between the Neanderthals and early modern humans, and his The Shanidar Neandertals (1983) explores the finds at Shanidar Cave in Iraq. George Constable, The Neanderthals (1973), is a useful introduction. Erik Trinkaus (ed.), The Emergence of Modern Humans (1990), discusses the human fossil and archaeological records as they relate to late archaic humans and the origin of modern humans. Erik Trinkaus and William W. Howells, The Neanderthals, Scientific American, 241(6):118133 (Dec. 1979), looks at the position of the Neanderthals in human ancestry and at their functional anatomy. Erik Trinkaus Cro-Magnons Marcellin Boule and Henri V. Vallois, Fossil Men (1957; originally published in French, 4th ed., 1952), is a well-illustrated general introduction to the field of fossil hominids, including an extended discussion of the Cro-Magnon peoples and the history of their discovery. L'Homme de Cro-Magnon: anthropologie et archologie (1970), contains a series of papers by specialists in physical anthropology and prehistoric archaeology on the skeletal biology and culture of the Cro-Magnon peoples. Andr Leroi-Gourhan, Treasures of Prehistoric Art (also published as The Art of Prehistoric Man in Western Europe, 1967; originally published in French, 1965), is a magnificently illustrated volume on the art of the Cro-Magnon peoples. Henri V. Vallois and G. Billy, Nouvelles Recherches sur les hommes fossiles de l'abri de Cro-Magnon, L'Anthropologie, 69(12): 4774 (1965) and 69(34): 249272 (1965), is the most thorough study of the skeletal biology of the human remains from the Cro-Magnon shelter. E. Genet-Varcin, Les Hommes fossiles: dcouvertes et travaux depuis dix annes (1979), provides a descriptive inventory of Cro-Magnon discoveries throughout the world. Henri J. Delporte Asia and Australasia R.L. Kirk and A.G. Thorne (eds.), The Origin of the Australians (1976), contains essays on the nature and origins of the Aboriginal Australians and their relationship to both their nearest neighbours and the rest of the world. G.G. Pope, Recent Advances in Far Eastern Paleoanthropology, Annual Review of Anthropology, 17:4378 (1988); and Rukang Wu and John W. Olsen (eds.), Palaeoanthropology and Palaeolithic Archaeology in the People's Republic of China (1985), provide overviews of H. sapiens discoveries and research. Atlas of Primitive Man in China (1980), compiled by the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Science, contains maps of fossil finds. Milford H. Wolpoff Africa Two essays in Paul Mellars and Christopher Stringer (eds.), The Human Revolution: Behavioural and Biological Perspectives on the Origins of Modern Humans (1989), are especially useful: Gnter Braer, The Evolution of Modern Humans: A Comparison of the African and Non-African Evidence, pp. 123154; and J. Desmond Clark, The Origins and Spread of Modern Humans: A Broad Perspective on the African Evidence, pp. 565588. Other essays include G.P. Rightmire, Africa and the Origins of Modern Humans, in Ronald Singer and John K. Lundy (eds.), Variation, Culture, and Evolution in African Populations (1986), pp. 209220; and C.B. Stringer and P. Andrews, Genetic and Fossil Evidence for the Origin of Modern Humans, Science, 239(4845):126368 (Mar. 11, 1988). Gnter Bruer General background to human evolution Hominidae as a zoological family Hominidae (superfamily Hominoidea, infraorder Anthropoidea, order Primates) is the taxonomic family that includes modern humans (Homo sapiens) and their direct extinct ancestors. Homo sapiens is the only species in the genus Homo of the family Hominidae that is living today, and extinct populations ancestral to man are known only from fossil bones and teeth. Earlier, extinct species of the genus HomoH. erectus and H. habilis, dating from the Pleistocene epoch (about 1.6 million to 10,000 years ago)clearly must be included in the Hominidae; and the genus Australopithecuswhich dates from the earlier Pliocene epoch (about 5.3 to 1.6 million years ago) and includes species such as A. africanus, A. robustus, A. boisei, and A. afarensisis also generally included in the family. Contrasting adaptations of Hominidae and Pongidae Hominidae are distinguished from Pongidae (anthropoid apes) by evolutionary trends that illustrate the adaptations of each for different environmental situations. The evolution of Hominidae Homo habilis The extinct species of the genus Homo called Homo habilis inhabited parts of sub-Saharan Africa at least two million years ago. In 1959 and 1960 the first Homo habilis fossils were discovered at Olduvai Gorge in northern Tanzania. These consisted of several teeth and a lower jaw associated with fragments of a cranium and some hand bones. As more specimens were unearthed workers began to realize that the hominids they represented were anatomically different from Australopithecus. Formal announcement of this and other discoveries was made by L.S.B. Leakey, Phillip Tobias, and John Napier in 1964. They described increased cranial capacity and comparatively smaller premolar and molar teeth as factors leading to the designation of the fossils as H. habilis and also suggested that the hand was capable of fine manipulation; Homo habilis thus seemed to foreshadow conditions seen in Homo erectus and in later humans. Fossil evidence Lower jaw of OH 7, found at Olduvai Gorge, Tanzania; the type specimen of Homo habilis. Apart from the jaw, cranial bones, and hand thought to represent a juvenile individual (Olduvai Hominid, or OH, 7) and recovered from Bed I deposits, several additional fossils from Olduvai have been ascribed to Homo habilis. At Bed II, at a site somewhat higher in the deposits than Bed I, pieces of another thin-walled cranium along with upper and lower jaws and teeth came to light in 1963. Just a month later a third skull was found in Bed II, but these bones had been trampled by cattle after being washed into a gully. Some of the teeth survived, but the cranium was broken into many small fragments; only the top of the braincase has been pieced back together. The two skulls from Bed II are numbered OH 13 and OH 16, and both are mentioned in the report prepared by Leakey, Tobias, and Napier in 1964. Since 1964 more material has been discovered, not only at Olduvai but at other African localities as well. One intriguing specimen is OH 24. This cranium is more complete than others from Olduvai ascribed to H. habilis. Because some of the bones are crushed and distorted, however, the face and braincase are warped and provide less anatomical information than they otherwise would. OH 24 is said to differ from Australopithecus in brain size and dental characteristics, but there are resemblances to the australopithecines of southern Africa in other features, such as face form. Partly because the fossil is damaged, complete agreement concerning its significance has not been reached. Important discoveries made in the Koobi Fora region of northern Kenya include the famous cranium numbered KNM-ER 1470. As in the case of OH 16, this specimen had been broken into many fragments, which could be collected only after extensive sieving of the deposits. Some of the pieces were then fitted into the reconstruction of a face and much of a large cranial vault. Brain volume can be measured rather accurately and is about 750 cubic centimetres (cc; 46 cubic inches). This evidence prompted Richard Leakey to describe KNM-ER 1470 as one of the oldest undoubted representatives of the genus Homo to be unearthed in East Africa. Some other features of the braincase are Homo-like, and many workers have accepted this opinion. At the same time, it is apparent that the facial skeleton is relatively large and flattened in its lower parts. In this respect, the Koobi Fora specimen resembles Australopithecus anatomically. Left side view of the KNM-ER 1813 cranium, found at Koobi Fora, Kenya. Among other key finds from the Koobi Fora region are KNM-ER 1813 and ER 1805. The former, which is most of a cranium, is smaller than ER 1470 and resembles OH 13 from Olduvai in many details, including tooth size and morphology. The latter skull exhibits some peculiar features. Although the braincase of ER 1805 is close to 600 cc in volume and is thus expanded moderately beyond the size expected in Australopithecus, a bony crest is formed along the top of the vault. This sagittal crest is coupled with another, more massive crest, oriented transversely across the rear of the skull. These ridges indicate that the temporal muscles (which function in chewing) and also the neck muscles were powerfully developed. A similar if more exaggerated pattern of cresting appears in what are referred to as robust australopithecines but not in Homo. Other features of ER 1805, however, are Homo-like. As a result, there has been disagreement among anatomists regarding the hominid species to which this individual should be assigned. Despite its anomalies, ER 1805 is probably best discussed along with other specimens grouped as Homo habilis. Several mandibles resembling that of OH 7 have been recovered from the Koobi Fora area, and teeth that may belong to H. habilis have been found further to the north, in the Omo River valley of Ethiopia. Some additional materials, including a badly broken cranium, are known from the cave at Swartkrans in South Africa. At Swartkrans the fossils are mixed in the Member 1 deposits with many other bones of robust australopithecines. An early species of Homo may also be present in the Member 5 breccias at Sterkfontein, not far from Swartkrans. Here again the remains are fragmentary and not particularly informative. A more recent and valuable discovery has been reported from Olduvai Gorge: in 1986 a jaw with teeth, cranial parts, and pieces of a right arm and both legs were located low in Bed I. The bones seem to represent one individual, called OH 62. Although the skull is shattered, enough of the face is preserved to suggest similarities to early Homo. The find is especially important because of the associated limbs, which show that OH 62 is a very small hominid indeed. The arm is long relative to leg length so that this individual has body proportions which differ dramatically from those of more modern hominids. The evolution of Hominidae Australopithecus Australopithecus (literally Southern Ape) was the generic name given to the first-discovered member of a series of fossils of creatures closely related, if not ancestral, to modern human beings. Since the first discoveryof a child's skull in a cave at Taung, S.Af., in 1924similar hominid remains have been found at numerous sites in East and southern Africa. The term australopithecine is often used to refer to all the fossil hominid material that dates between the last half of the Late Miocene epoch (about eight to 5.3 million years ago) and the beginning of the Pleistocene epoch (around 1.6 million years ago). Fossil remains that date from before eight million years ago are widely regarded as those of fossil apes, while evidence of Homo erectus (Upright Man) dates to about the beginning of the Pleistocene. The remains of Homo habilis (Handy Man) have been recovered from sites between 2.5 and 1.5 million years old. These are more easily confused with those of Australopithecus, and the final allocation of some of this material is still being debated. The fossil evidence of the australopithecines has been seen by some scholars as merely representing temporal stages within a single evolving hominid lineage leading to Homo erectus and thence to Homo sapiens. Others have stressed the extent of the adaptive differences between the various fossils and have suggested that there may have been two, or even three, lineages evolving in parallel, only one of which led to the later species of Homo. Whatever the details of their interpretations, however, most hominid paleontologists are agreed that the australopithecines represent a linkdirect or indirectbetween the fossil apes and human beings. Thus, the study of the australopithecines is regarded as the study of one of the most important stages in the emergence of modern H. sapiens. Fossil evidence The South African australopithecines More than a decade was to elapse between the recognition of the importance of the Taung child's skull by Raymond Dart in 1924 and the next series of discoveries of australopithecines in southern Africa. These latter discoveries were made by Robert Broom in 1936 and 1938 as the direct result of mining operations in the Transvaal region at the caves of Sterkfontein and Kromdraai, several hundred miles northeast of Taung. When research activities resumed in earnest in South Africa after World War II, two additional cave sites were discovered at Swartkrans and Makapansgat. After the early discoveries the rate of recovery of fossils from these hard, breccia-filled cave deposits diminished. During the 1970s, however, there was renewed activity at these sites, and the total number of hominid remains recovered from southern African caves is well in excess of 1,000. As each series of discoveries was announced, it was usually marked by the suggestion of a new species, if not genus, for the newly found fossils. Scientists are now agreed, however, that the evidence does not justify the multiplicity of taxa that resulted. It is generally accepted that the australopithecine fossils recovered from these cave sites belong to either Australopithecus africanus, the species usually referred to as the gracile australopithecine, or A. robustus, the species called the robust australopithecine. (Some workers support the recognition of a second species of robust australopithecine found at Swartkrans, called A. crassidens, but this is a minority view.) The classification into two main species within one genus won the support of Dart and Sir Wilfred Le Gros Clark, and, with minor modifications, it is the scheme that has come to be supported by the majority of scholars. The labels gracile and robust are useful because they are widely understood, but they also are dangerous in that such a simple classification is misleading. An increasing number of workers have argued that the generic name Paranthropus (Next to Man), coined by Broom in 1938, should be revived to distinguish the robust australopithecines. The skull of Australopithecus africanus has a braincase that is roughly spherical in shape, with the greatest width across the base of the skull. The cranial capacity of the species depends upon which estimates are used; the average value is probably between 430 and 450 cubic centimetres (26 and 27 cubic inches), a capacity just within the range of that of living apes. Brain size is best judged in relation to body size, however, and on this count the gracile australopithecines have a relative brain size intermediate between that of modern apes and that of modern human beings. The area of attachment on the skull for the neck muscles is reduced when compared to that of equivalent-sized apes. Although bony crests mark the attachment of the jaw muscles onto the skull, these are not obvious features and, in particular, do not form large midline, or sagittal, crests. The foramen magnum (the area of the skull through which the spinal cord passes) lies nearer the centre of the skull in these fossil hominids than it does in the apes. The face is projecting, but it does not form the marked muzzle that is a feature of most modern and fossil ape skulls. The teeth of the gracile australopithecines are not arranged in the characteristic U-shaped fashion of the apes but instead lie in a more rounded arcade. The incisor teeth are set vertically in the jaw, and the canines are small and do not project above the other teeth, which is always the case in the apes. There is no gap, or diastema, between the canines and the premolars, and the upper canines do not form a shearing unit with the first lower premolars. The milk teeth resemble those of the later hominids, but the order of eruption and the rate of maturation of the teeth follow the ap