Early hominids began leaving Africa for Asia almost one million years earlier than previously thought. What drove these migrations?
This article was published by American Scientist, November-December 1996.
|An early hominid, Homo ergaster, depicted in this diorama from
the American Museum of Natural History's Hall of Human Biology and Evolution,
lived nearly 2 million years ago in the eastern Rift Valley of Africa.|
Until recently, anthropologists thought that such early hominids did not disperse from Africa to Asia until 1 million years ago. New fossil finds and dates from Asia, including the authors', now suggest that early Homo arrived in East and South Asia by 2 million years ago. Tying the new evidence to paleoclimate and ecological theory, the authors suggest that the physical adaptations of African emergence-among them, a ranging bipedal gait, stone technology, increased intelligence and extensive scavenging-may also have enabled early Homo to colonize subtropical Asia very quickly.
The most basic questions for human dispersal have remained hypothetical during the past two decades. When did hominids first leave Africa? Which species was the first to leave? Why did they leave? The issue of age has always overshadowed all others. In the eastern Rift Valley sites, fossils are usually recovered from relatively fine-grained deposits laid down by water and wind. These formations often include layers of volcanic ash that are easily dated using the potassium-argon (K-Ar) radiometric method. Alternatively, in Europe and subtropical Asia many fossils are found within the diverse and complex deposits that accumulate in caves, where depositional histories are difficult to interpret and volcanic materials are not present. The net effect is that the age of Homo fossils has been measured more precisely (and consistently older) in Africa than in Eurasia. Thus, the earliest Homo erectus (better termed Homo ergaster) fossils in the eastern Rift Valley appear fully developed by 1.9 mya, whereas the Javanese fossils (classic Asian Homo erectus), which are thought to be the earliest in Asia, have traditionally received broad age estimates of only 700,000 years to 1.1 million years. The nearly one-million-year disparity between the African emergence and the initial Asian arrival has for years been the basis of the conventional theory for a late dispersal.
Recent developments in techniques that provide the absolute ages of artifacts--such as paleomagnetism, electron-spin resonance (ESR), and single-crystal argon (Ar/Ar) methods--have shed new light on the arrival of Homo in Asia. Moreover, the discovery of new artifact-bearing sites makes the dispersal of Homo a much more accessible question. At Riwat and Pabbi Hills in Pakistan, simple stone tools have a paleomagnetic age of about 1.9 million years. At Sangiran and Mojokerto in Java (Indonesia) the sedimentary contexts for three well-known cranial specimens of Homo erectus now have Ar/Ar age determinations of 1.6 to 1.8 million years. The most intriguing of the new finds for early Asian dispersal come from Longgupo, a cave in southeastern Sichuan Province, China. The Longgupo hominid teeth have affinities to early African Homo and the stone artifacts resemble early African tools. Last year, we and our Chinese colleagues, Huang Wanpo and Gu Yumin at the Institute for Vertebrate Paleontology and Paleoanthropology, published ESR and paleomagnetic analyses that indicated an age of 1.9 mya for the Longgupo remains. The growing number of Asian hominid fossils and stone-tool assemblages that approach 2.0 million years in age now suggests that an early population of Homo arrived in eastern Asia within a few hundred thousand years of arising in Africa. In the light of this new evidence for early dispersals, it appears Homo emerged not so much in adaptation to challenging conditions, but fully poised to dominate new resources in new territories.
|Figure 2. Evolution of the genus Homo from Australopithecus seems to be linked with global climate changes between 2 and 3 million years ago. Cooler temperatures diminished the tropical-woodland habitat of Australopithecus in favor of more open savanna. Several species of Homo evolved rapidly to occupy these new habitats, as did Paranthropus , another descendant of Australopithecus . Paranthropus became extinct by 1.2 million years ago. Early Homo maintained a generalized anatomy as it spread throughout tropical and subtropical Asia, but apparently became specialized with the evolution of Homo erectus by 1.8 million years ago. The much later European dispersal of African Homo heidelbergensis also seems to have resulted in the specialized Neanderthals. All of these early dispersals of Homo were apparently eclipsed by the late Eurasian dispersal of Homo sapiens , from Africa, some 100,000 years ago. The three darker bands indicate periods of greater relative aridity.|
|Figure 3. Hominids now known as Homo erectus were found on Java,
Indonesia, in 1891, and at Zhoudoudian, near Beijing, in the 1930s. As
Homo erectus was clearly more primitive than hominid fossils known
in Europe, human beings were initially thought to have emerged in East
Asia and dispersed westward. Since the early 1960s, numerous fossils from
African localities in the eastern Rift Valley, Lake Malawi and South Africa
have demonstrated an African emergence for Homo . In the 1990s,
advances in dating methods and new finds at Dmanisi (Georgia), Riwat (Pakistan),
two Javanese sites and Longgupo (China) show that early Homo had
arrived in East Asia by 2 million years ago. Areas in pale blue indicate
land masses submerged since those early dispersions.|
| Please click on an image above
to see the full size version..|
Emergent Biological Technology
As typified by Homo ergaster, early Homo was the first hominid to develop a ranging bipedal gait, one that allowed it to cover a lot of ground in a short period. Long, well-muscled limbs on a lanky torso also conferred physical strength and defensive presence. Leverage and strength in the arms and hands gave early Homo the ability to make simple chopping and cutting implements. Whereas Australopithecus and Paranthropus had significant sexual dimorphism in body size and strength, early Homo did not. Among other primates, reduced sexual dimorphism usually means that both sexes perform similar economic activities, that males compete less physically among themselves for females and that males and females pair-bond for long periods. An enlarged cranium also typified early Homo. A larger brain may have bestowed a more flexible intelligence, useful for finding resources within new habitats, as well as the complex behavior Homo came to use against prey and predators.
The early specimens of Homo also exhibit the relatively diminished premolars and molars-the cheek teeth-of an omnivorous eater, one for which animal protein played a significant dietary role. As a part-time meat eater, early Homo probably relied on large carnivores to supply many usable packages of animal protein-very pragmatically scavenging the remains of what real carnivores could more effectively hunt. At the other dietary extreme, these hominids certainly consumed some hard, tough plant foods. In contrast to Paranthropus, whose digestion of such foods probably began inside its mouth, early Homo more often and more completely processed difficult animal and vegetal resources with stone-tool technology, which was employed to break, crush, split and cut up hard foods before ingesting them. Rather than being implements of predation, early tools underlay a technology that essentially added a new first stage to digestion. Indeed, we hypothesize a close relationship between Pliocene hominid biology and a very elementary technology, in effect a "biological technology" in which both the mass and the jagged edges of a few chipped rocks gave early Homo access to a wide range of nutritional resources. Simple stone tools represent immediate extensions of the forelimb and hand for breaking down or processing tough foodstuffs.
|Earliest complete skeleton of Homo is that of a boy from the West Turkana region of Kenya. Homo ergaster already had many anotomical features of Homo sapiens, including a high, domed cranium with realatively light cranial and facial bones and a lanky torso with long, well-muscled limbs. The overall size and proportions of its skeleton gave Homo ergaster a ranging, bipedal gait as well as physical strength and a defensive presence. Leverage and strength in the arms and hands helped this hominid use simple stone tools effectively to chop and crush food. (photograph provided by Alan Walker at the Pennsylvania State University and reproduced with permission from the National Museums of Kenya.)|
Hominid biological remains may be difficult to classify,
but stone tools present even greater problems of interpretation. One way to
understand the development of early stone technology is to envision emergent
and advanced stages separated by a transition. Currently, evidence for the emergent
stage appears with the late-middle Pliocene (about 2.5 mya) in Hadar, Omo and
Turkana. Mzalendo Kibunjia of the National Museums of Kenya has proposed the
name Omo Industrial Complex for such assemblages, in which rocks were broken
or casually chipped into very basic implements. Only a few general tool types
can be defined for the Omo-type assemblages: simple core choppers and rough
flake scrapers. The basic technological characteristics of Omo-type core-flake
assemblages vary by the raw materials available in each region. In Hadar and
Turkana, where large volcanic cobbles are present, the tools tend to be large
and the chipping technique a little more complex. In Omo, where small, tough
quartz cobbles were used, the tools are much smaller and more haphazardly made.
At present, the Omo-type localities and tools represent the initial threshold
of stone technology at a date that correlates well with the emergence of Homo
The advanced or Acheulian stage begins with the early Pleistocene, about 1.6 to 1.4 mya-well after Homo ergaster attains full development in the Turkana Basin. The Acheulian technological complex is achieved as the selection of raw materials, the preparation of the stone core and the chipping procedures become much more complex, and the tools themselves become somewhat specialized. Bifacial chipping is the hallmark of the Acheulian Industry. With this technique, a tool blank is chipped from two directions across a bisecting plane. The blank is worked around a circumferential edge to resemble a plump discus, or a double-sided tortoise shell, and the entire edge becomes the working part. Although earlier hominids had developed crude bifacial techniques by 2.0 mya, the method did not become the basis for a distinctive set of Acheulian biface tools until about 1.5 mya. The Acheulian appears to emerge in the eastern Rift in areas such as Konso-Gardula in Ethiopia, as well as Peninj and Olduvai Gorge in Tanzania. Nevertheless, Acheulian bifaces are found as far north as the Jordan Valley of Israel (at 'Ubeidiya) by 1.4 mya. When hominid remains and early Acheulian tools are associated within any site stratum in Africa, the species is always Homo ergaster or Homo erectus, not Homo habilis or Paranthropus boisei.
The period from about 2.0 to 1.5 mya is best seen as a long and important transition between the advent of chipping techniques and the achievement of standardized Acheulian biface tools. Much of this period is represented in the lower beds of Olduvai Gorge, Tanzania, where Mary Leakey of the National Museums of Kenya defined the well-known Oldowan Industry more than 30 years ago. At the time, the Oldowan was thought to be the earliest manifestation of stone technology and, indeed, the earliest assemblages in Bed I (the oldest levels of Olduvai) resemble those from Ethiopia and northern Kenya now deemed oldest. Nevertheless, most Oldowan tool kits reflect more care and skill in choosing raw materials and in preparing and striking cores to create usable flakes and core tools than do the Omo-type assemblages. Over the several hundred thousand years evident in Olduvai's stratigraphy, Oldowan assemblages undergo distinct refinement in chipping techniques and some standardization in tool form. By 1.7 to 1.6 mya, bifacial tools help to define the Developed Oldowan Industry. At Olduvai, the initial stone tool finds came in stratigraphic association with a new hominid, one with a larger brain and more gracile features than had the previous robust australopith skull found at Olduvai Gorge (Paranthropus boisei). The clear association of an advanced hominid with stone tools prompted the Leakeys to designate the new species Homo habilis, literally "handy man." It becomes clear that more than one species of Homo--and probably Paranthropus boisei--made Oldowan-type tools at Olduvai Gorge and elsewhere.
Given its relatively early appearance and greater complexity over the earlier stages as well as its association with Homo ergaster, the African Acheulian technology has often played into hypotheses for Eurasian dispersal. However, new dates and technological analyses make any such role unlikely in Asia. Although Acheulian tools always seemed to antedate the earliest tool assemblages in East Asia, the recently discovered stone tools at Longgupo and Riwat are as ancient and as simple in design as their Omo and early Oldowan counterparts in Africa. None of the older Asian assemblages contain handaxes, and few exhibit even the standardized chipping patterns of the Developed Oldowan or the Acheulian technologies.
The current and revolutionary evidence for a very early dispersal of hominids from Africa to Asia may be reiterated as follows. Fragmentary fossils representing the emergent genus Homo are consistently dated to nearly 2.5 mya at various points in the eastern Rift Valley. Likewise, as the earliest stone tools, also found in the eastern Rift, have equal antiquity, the emergence of one must be linked to the other. By 1.9 mya, Homo ergaster presents undeniable morphological features for moving great distances: long torso and limbs, narrow hips, a large brain and reduced dentition. With the new evidence from Longgupo, Java and Riwat, it becomes clear that early Homo (the immediate ancestor to Homo ergaster and Homo erectus) and simple stone tools arrived in tropical and subtropical Asia by about 2.0 mya. The emergence of Acheulian technology in east Africa confirms the hypothesis for early Asian dispersal. Distinctive bifaces date to 1.5 mya in the eastern Rift Valley and the Middle East, and to 600,000 years ago in Europe. The absence of Acheulian bifaces at the early sites in south or East Asia suggest that Homo must have initially left Africa before the Acheulian stage appeared in Africa. Consequently, early Homo dispersed to subtropical Asia with a very elementary technology.
|Stone technology appears to have emerged in the eastern Rift Valley about 2.6 million years ago. At this time, tools of Omo Industrial Complex appeared, in which early Homo toolmakers chose a durable crystalline stone, often picked off the ground as a fist-sized cobblestone, to break or chip into a core and several flakes (top).|
|By 1.6 to 1.4 million years ago, raw-material selection, core preparation and chipping techniques had improved markedly. In reorienting the core and hammerstone, Homo ergaster toolmakers could chip flakes from a lenticular cobble around its periphery on both faces (bottom ). Competent bifacial chipping, the hallmark of Acheulian artifacts, was a skill carried to Europe by Homo heidelbergensis about 600,000 years ago. Having attributes of both Omo and Acheulian tools, Oldowan artifacts, first recovered from Olduvai Gorge in the 1960s, reflect an intermediate technological stage lasting from about 2.0 to 1.5 million years ago.|
Having established the Middle Pliocene climatic window, the coincident technological threshold and the early dates for arrival in Asia, it is now possible to hypothesize the process of early dispersal within a strong theoretical framework. We believe that the ecological context of emergence holds the key for understanding early Asian dispersal. Clearly, interactions between populations and their environments influence evolutionary change, including dispersion. Change in environmental conditions, such as climate, inevitably bring neighboring populations into competition for shelter, food and other resources. Populations may respond either by specializing to create a new niche within the old territory, or by dispersing to relieve pressure in the home territory and to establish or maintain the old niche in new territory. Alan Turner of the University of Liverpool has pioneered research that ties hominid dispersals to the better-known movements of more common mammalian species. His consistent point is that hominid evolution should not be viewed as unique or separate from the general processes that govern change in a host of related species.
Our ecological model addresses the scavenging behavior that we believe constitutes the primary behavioral factor for early dispersal. The model relies on the results of detailed regional survey and site excavation within the eastern Rift Valley by a number of archaeologists. Over years of research, the stone and bone detritus recovered at hominid occupation sites has been shown to reflect, quite sensitively, specific natural resources used and the ways in which resources were collected. Working together, archaeologists and paleoanthropologists have found that diverse research areas such as Olduvai Gorge, the Omo Valley and the Turkana Basin yield somewhat different patterns of early hominid occupation for any given period, based on the availability of stone raw materials for tools and water resources. Nevertheless, when compared through time, the localities exhibit basic similarities in hominid scavenging practices and technological tradition that form the African background for early Asian dispersal. Jack Harris of Rutgers has been instrumental in bringing forth the earliest evidence for stone tools and their behavioral implications. Much of our model follows the lead of Harris and his colleagues and students.
|Figure 7. Early stone artifacts show technological development in Africa
and the Middle East, but none in subtropical Asia, where stone technology
seems to have arrived and remained at Omo and Oldowan levels. Hammerstone
and core tool from Olduvai Gorge, Tanzania (a ) helped define the style
of tool called Oldowan. Flake and core tools from Lokalelei, Kenya, (b)
are of the Omo type. Core tools of the Oldowan type were found in 'Ubeidiya,
Israel (c ), as were Acheulian bifaces (d ). Core tools were found in
Longgupo, China (e ), Riwat, Pakistan (f) and Dmanisi, Georgia (g ). Bars
connect two views of the same tool. Scale is 1 inch = 15 centimeters|
Eastern Subtropical Habitats
Given the crucial technological advantages and catchment-scavenging strategies, early Homo should have out-competed other hominid and nonprimate scavengers within expanding open landscapes. This pattern of behavior created essentially a hegemonic ecological niche dependent on rapid, extensive and possibly aggressive movements. In this regard, south and East Asia offered new opportunities to scavenge and perhaps to hunt animals unaccustomed to the presence of hominids. Asia would also have presented fewer constraints in the form of large primate competitors and large carnivorous predators as well as endemic parasites and diseases. Moreover, an elementary stone-tool technology would suit catchment scavenging in Asia, as it does not require supplies of good-quality stone for specialized chipping and handaxe production. Fist-sized river cobbles of workable stone obviously served Asian hominids well enough. By gradually making its way among sparsely distributed open catchments, early Homo (now a global scavenger) could have reached East Asia within a few hundred thousand years of emerging in eastern Africa.
As mentioned, the earliest and most convincing new evidence for early Asian dispersal comes from Longgupo, Sichuan Province, China. Our Chinese colleagues, Huang and Gu, asked us to collaborate in analyzing the hominid teeth and artifacts, and in verifying the ancient age of the cave deposit. The finds at Longgupo include a jaw fragment with premolar and molar teeth, an isolated incisor and two stone artifacts. The incisor has a primitive form of "shoveling," where the sides and base extend rearward to form a depression on the center of the rear surface. This feature is well known for Homo ergaster. Fourth-premolar (second bicuspid) and first-molar cusp patterns also show affinities with Homo ergaster. The two artifacts are cobblestones of volcanic rock that have been slightly modified into tools for chopping and battering, much like the African Omo tools.
|Collapsed cave of Longgupo in eastern Sichuan Province, China, has recently yielded important hominid fossils and stone artifacts for which the authors have established a date of nearly 2 million years. The hominid remains and artifacts lie in geological association with many other mammalian fossils that provide sensitive evidence for species movement. In addition to the arrival of early Homo, the Longgupo fauna indicates that subtopical species of horses and pigs also moved to new northerly limits during the late Pliocene.|
|Jaw fragment from Longgupo cave (left), which dates to about 1.9 million years ago, resembles an analogous specimen (right) from East Turkana (ER 992), dated to about 1.2 million years. Both fossils show more generalized hominid dental features in molar cusp patterns and premolar crown shape when compared with Asian Homo erectus. The Longgupo jaw is thus more primitive than Homo erectus and could represent the ancestral condition for that species. The Longgupo hominid best represents a population of early Homo arriving to East Asia about the time Homo ergaster appears in Africa. (Photograph of African hominid jaw provided by Alan Walker and reproduced with permission from the National Museums of Kenya. Longgupo photograph courtsy of the authors.)|
In introducing our argument,
we noted that Eugene Dubois began collecting fossil hominids on the island of
Java before the turn of our own century. Since Dubois's time, more than 80 cranial
specimens of have been found at six principal localities. Although the localities
generally have complex stratigraphies, the fossils have been collected without
reliable stratigraphic information. However, two Javanese localities, Mojokerto
and Sangiran, stand out for having Homo erectus fossils associated with
the Pucangan Formation, which has been dated independently at nearly 2.0 mya.
Recently, Carl Swisher at the Berkeley Geochronology Center and his colleagues
have reconfirmed the geological associations and have applied Ar/Ar techniques
to Pucangan deposits at these sites. Sediments from the Mojokerto site, in which
a well-preserved juvenile skull has been found, yield an average age of 1.81
mya. Sediment from Sangiran, in which two other crania were found, gives 1.66
mya. The new ages for these three specimens show that the low cranial vault,
thick cranial bones and massive face that characterize Homo erectus evolved
rapidly after early Homo arrived in Asia. Very recently, Truman Simanjuntak
of the National Research Centre of Archaeology in Jakarta and François Sémah
at the Musée National d'Histoire Naturelle at Paris have found simple but indisputable
flake tools in the Kabuh Formation, which overlies the Pucangan. Although these
artifacts were deposited more recently than the remains of the earliest hominids,
the discovery puts tools in the hands of Javanese Homo erectus in general,
for which any such association had been lacking.
The technological component of early dispersal also appears southeast of Rawalpindi, Pakistan, among some large tributaries of the Indus River. Two areas, Riwat and the Pabbi Hills, have been studied by British and Pakistani specialists. A small number of simple flaked quartzite tools were found at Riwat during the 1980s, and a larger core-flake assemblage was recovered from the Pabbi Hills locality. Geological associations and a paleomagnetic analysis suggest an age of nearly 2.0 million years for the Riwat deposit, and more circumstantial evidence points to a similar age at Pabbi Hills. The consistent technological feature of all the earliest Asian stone-tool assemblages is simplicity. Indeed, all assemblages, including the later tools from Sangiran, recall stone artifact assemblages from either the Omo or Oldowan technological complexes but not from the Acheulian.
How could groups of scavenging hominids employing the simplest of technologies spread across south and East Asia so quickly? Middle Pliocene cooling and drying also encouraged South Asian dispersal as a band of open tropical and subtropical environments appeared from the area that is now Saudi Arabia eastward south of the Himalayas and into Southeast Asia. Like the African grasslands, these habitats (of more mixed vegetation types) drew catchment-scavenging hominids. Moreover, by the late Pliocene a significant portion of the earth's moisture was locked in glacial ice mass, lowering the global sea levels to expose what is now the continental shelf as expansive areas of coastal plain or to reveal isthmuses where there are now straits. Two exposed areas would have facilitated eastward dispersal. The Bab-el-Mandab (linking Africa and Asia between modern-day Djibouti and Yemen) adjoins Hadar, with its very early stone-tool assemblages. This short isthmus would have produced the best departure point for eastward travel within the tropical zone. The presence of similar modern flora and fauna (including Hamadryas baboons) on both sides of the strait signal its importance for numerous dispersals. Departing Africa on this route, early Homo could trend east-northeast across the Arabian Peninsula to reach a much smaller Persian Gulf, possibly crossable at Hormuz. A short journey east along the Arabian Sea brings the Indus Valley and direct access to Riwat and Pabbi Hills. Thus, although these South Asian sites seem to be along way from Africa, the departure point of Hadar lies surprisingly close given late Pliocene geography. A route south of the Himalayas would have brought early Homo to Southeast Asia.
Within the lowland Southeast, hominid groups would have encountered the large land mass of the Sunda Shelf, which then linked the tropical Southeast Asian archipelagos (including the island of Java) to the mainland. In our own century, dredging and fishing on areas of the Sunda Shelf that are now offshore have yielded Pleistocene fossils of large mammals. Although modern-day Longgupo appears inaccessible from these lowlands because of the eastward drainage of the upper Yangtze River, during the Pliocene the river drained southeast toward the Gulf of Tonkin. Like northern Pakistan, inland south-central China could have been reached directly from the south by ascending a broad alluvial valley. Indeed, paleontologist John van der Made of the Rijksuniversiteit Utrecht notes that in association with the hominids at Longgupo, subtropical species of horse and pig appear rather early at their northerly limits.
Western Temperate Habitats
If early Homo was able to disperse early and quickly across subtropical East Asia, why does it seem to arrive later in West Asia and yet later in Europe? For West Asia, the sites of 'Ubeidiya in the western Jordan Rift of Israel, and Dmanisi, southeast of Tblisi, Georgia, provide the most information on early occupation. 'Ubeidiya's 150 vertical meters of geological infill appear to have been deposited over a short period. The assemblage of animal fossils in the stratigraphic column suggests that much of the deposit dates to nearly 1.4 mya. The lower archaeological levels contain a range of stone flakes and tools, some having the standardized forms associated with contemporary assemblages in East Africa, but there are no biface tools. The upper levels, not greatly different in age, clearly have these Acheulian tools. As only a few isolated human teeth have been recovered from the site--only one in geological context-the hominids responsible for the stone tools remains unknown. Ofer Bar-Yosef of Harvard University interprets the sequence as the result of two separate hominid occupations within a relatively short time. Both groups shared an advanced core-tool technology; one group used biface tools, the other did not.
|Figure 10. Early Homo managed natural resources to minimize dependence on specific territories. The simple strategy for "catchment" scavenging is evident in eastern Rift Valley archaeological sites older than 2 million years. A group of hominids using this strategy established a camp conveniently close to multiple primary resources, such as water, stone and animal carcasses (red marker in the foreground). The catchment becomes the area around the camp within which resources are distributed sparsely but still readily available (blue markers ). Archaeological remains at catchment camps are rich and diverse, whereas little material is found at outlying points. After 2 million years ago, Homo ergaster 's scavenging strategy became decentralized. This hominid ranged among more points within a larger "territory," a behavior that required more intimate knowledge of scattered resource points. Territory-site assemblages are thus smaller and more specialized, each reflecting localized resources. Rather than getting to know a landscape intimately, early Homo traveled widely among catchments (red markers in the background ), thus increasing its ability and chance to disperse widely.|
Early Dispersal and Homo sapiens
If early Homo was able to leave Africa before 2.0
mya (and later), did these intercontinental quests contribute to the prehistoric
distributions of Homo sapiens, our own species? The new evidence must
be framed in terms of the ongoing debate over "multiregional" or "out-of-Africa"
origins for Homo sapiens. The multiregional argument would use the
new evidence to suggest that the early dispersals of early Homo set
a complex stage for Homo sapiens to emerge at connected points across
much of the Old World. For us, however, the new evidence suggests that both
the early and later species of Homo had the ability to disperse across
the continents. Given that Homo sapiens fossils appear to be much older
in Africa than on any other continent, the answer seems obvious. Having emerged
in Africa, Homo sapiens dispersed to Eurasia, replacing older populations
Although there is little question that Homo sapiens emerged in Africa, the date of emergence, the technological associations and the dates for its Eurasian dispersals are debatable. It appears that our species originated between 200,000 and 100,000 years ago, somewhere in sub-Saharan Africa. Some recent discoveries in Zaire of ancient and finely crafted tool types (such as barbed-bone harpoons) indicate that the technology associated with this emergence may have been very advanced indeed, resembling the much later Upper Paleolithic of Europe. In the Levant, where Homo sapiens is evident about 90,000 years ago, a more archaic Middle Paleolithic technology still held sway. Consequently, we may not yet say whether the European dispersal of Homo sapiens was associated with either its emergence or a new technology.
|Figure 11. Dispersal corridors opened out of Africa and across the Middle East into South and East Asia during the late Pliocene. Corridors formed primarily along coastal land masses, the product of expanding polar ice caps and resultant sea-level drawdown. Incipient development of the Red Sea rift also established departure routes through the Middle East. The drop in sea level in island Southeast Asia would have connected Sumatra, Java and Borneo with the mainland. Evolutionary analysis of fossil species, including antelopes, pigs and cats, indicates that large mammals dispersed along these routes sporadically during the late Pliocene and early Pleistocene. New fossil finds suggest that early Homo arrived in Asia some 1.8 to 1.9 million years ago, after departing Africa at least 100,000 years earlier.|
In linking the early dispersal of early Homo with its emergence, we are describing a hominid very different from the australopiths, whose bipedal but still ape-like anatomy must have limited them to wooded locales. Thus the significance of an early dispersal to Asia is manifold. First, the climatic conditions of cool aridity that played a great role in the emergence of Homo itself also drew hominid populations out of Africa and into Asia. Emergence and dispersal are, to a great extent, a product of environmental change. Nevertheless, early Homo emerged with a radical, yet still generalized, set of characteristics that granted it ecological hegemony across the subtropical Old World. An early intercontinental distribution signifies a hominid not adapted to specific territorial conditions, but adapted to manage many local conditions through physical presence, technology and flexible social organization. Ironically, as the first species to use technology, early Homo colonized much of the subtropical Old World without the benefit of language, symbolic culture or individual consciousness as we know it.