Genetic data and physical proximity suggest that northeast Africa provided the immediate source area for the dispersal from Africa. There is evidence from Lake Naivasha in Kenya that East Africa was relatively well watered about 60,000 years ago, and data from both Antarctic and Indian Ocean cores suggest that the climate was relatively warm at that time, perhaps providing the right environment for population growth and another acceleration in innovation. There are many Middle Stone Age sites in Ethiopia, Kenya, and Tanzania that demonstrate human occupation around this time, but their study and dating are still largely in progress, and so it is difficult to relate them precisely to the time of the modern human dispersal from Africa. An example is the rich site of Magubike rock shelter in Tanzania, being excavated by Pamela Willoughby and her colleagues, where I am involved in the study of fossil human teeth. But there are published findings from one important site: a rock shelter near Lake Naivasha, Enkapune ya Muto (Twilight Cave). This lies close to sources of obsidian (a volcanic glass highly prized for making stone tools) at an elevation of 2,400 meters, with a rich record of Middle Stone Age and succeeding Later Stone Age occupation. The earliest levels of the latter industry show many innovative features such as specialized tools, red ocher use, and ostrich egg shell beads, dated to more than 46,000 years old.
In chapter 4 I discussed routes out of Africa and possible connections between North Africa, the Middle East, and Europe between 40,000 and 50,000 years ago. The most obvious pathway out of Africa would have been up the Nile Valley, through Sinai, and thence into the Levant (the region adjoining the eastern Mediterranean coast). Suggestions that another route could have existed at the other end of the Mediterranean—by boat across the Strait of Gibraltar—are appealing when one considers that the Strait was narrower during the last glacial, and there may even have been intervening islands at times. But good archaeological or fossil human evidence of an ancient connection is still elusive, with no sign of true Neanderthals in North Africa, nor of moderns at an early date in southern Iberia. On the contrary, the region seems to have been one of the last outposts of the Neanderthals. It is possible that populations did cross from time to time but could not gain a foothold, but the fact that Mediterranean islands like Malta, the Balearics, Sardinia, and Cyprus do not seem to have been impacted by humans until much later also speaks against such mobility by early moderns and Neanderthals (although there are recent claims that African-looking handaxes were discovered on Crete).
But what about pathways farther east? We saw that there is evidence of the use of coastal resources in South Africa during the Middle Stone Age between 60,000 and 160,000 years ago, at sites like Pinnacle Point, Blombos, and Klasies River Mouth Caves, and the pattern is matched at sites scattered around the North and East African coasts, with a particularly interesting example at Abdur, on the Eritrean Red Sea, dated to the high sea level of the last interglacial, about 125,000 years ago. In the 1960s the American geographer Carl Sauer proposed that “the dispersal of early man took place most readily by following along the seashore. The coasts ahead presented familiar foods and habitats … Coastwise there was scarcely a barrier to the spread … through tropical and subtropical latitudes … The Indian Ocean, likeliest sea of earliest human occupation, exhibits to a large extent … an inviting articulation of shoreline, from Africa to the Sunda Islands [of southeast Asia].”
Some thirty years later the zoologist Jonathan Kingdon suggested that Middle Stone Age people left Africa through the Middle East and reached southeast Asia by 90,000 years ago, where they adapted to coastal living, including the development of a boat- or raft-building capability. This enabled them both to return westward to Africa and to move southward to Australasia. The anthropologists Marta Lahr and Robert Foley proposed in their Multiple Dispersals model that a more direct route from Africa to Arabia and farther east could have been taken before 50,000 years ago, perhaps using the coasts, and exiting by boat across the Bab-el-Mandeb strait at the southern end of the Red Sea. Geneticists such as Spencer Wells and Stephen Oppenheimer have also favored this route, arguing that only a few hundred people may have made the fateful crossing into Arabia, to found the populations of the rest of the world.
Personally I have never seen the necessity of invoking this complication in our African exodus, since if people were on the western coast of the Red Sea they would only have needed to travel north, around Sinai, and then south again down the eastern coast of the Red Sea. Continuing along the narrow ribbon of shoreline, to which they were already adapted, they could have progressed within a few millennia all the way to Indonesia at times of low sea level, and could have been spared the level of habitat disruption faced by inland populations during the rapid climatic fluctuations of the late Pleistocene. Population increase or depletion of resources would have driven the dispersal, and the development of watercraft could have followed from the need to traverse natural barriers such as dense mangrove forests or river estuaries, or to extend coastal foraging opportunities. These coastal populations could then have penetrated up river valleys into the interior, and by the end of their journey through southeast Asia, they would have been ready for the (probably fortuitous) first steps toward New Guinea and Australia (then joined as one enlarged continent).
The region of Arabia probably did form an important transit route for Out of Africa pioneers, but until recently it was largely terra incognita in terms of hard data, leading to much theorizing. Recently, however, several international teams have been trying to fill this void through fieldwork in the area. Archaeologists like Jeffrey Rose and Michael Petraglia have argued that it was not just a place that people passed through but an important locus for early humans in its own right. When environments were hyperarid in western Asia, it provided refuge with its ephemeral rivers and lakes, and its coastal margins, as these were exposed by falls in sea level. Despite the confounding lack of diagnostic fossil evidence, research by Simon Armitage and his colleagues at Jebel Faya (United Arab Emirates) provided important clues that early modern humans might even have dispersed from Africa, across Arabia as far as the Straits of Hormuz, by 120,000 years ago. This research augments the controversial idea that such modern populations could have migrated even farther across southern Asia, despite the conflicting genetic data that movements only occurred after 60,000 years. However, the fact that the artifacts at Jebel Faya look “African” and do not resemble those associated with the contemporaneous Skhul and Qafzeh people in the Levant signals yet more complexity in the exodus of modern humans from Africa. Could there have been separate early dispersals, one from East Africa into Arabia and another from North Africa into the Levant? And what was the fate of these different populations 100,000 years ago? Did they die out, did they survive in small pockets, did they perhaps interbreed with neighboring archaic peoples, or could they indeed have spread farther eastward?
After suffering colder and drier conditions, the climate in southern Asia improved with the temporary return of a strong summer monsoon about 57,000 years ago, and this may have helped the survival and migration of modern humans across India toward southeast Asia and Australasia at this time. However, signs of “modern” traits such as symbolism and complex technology are hardly apparent until after 45,000 years ago—a subject we will discuss later in this chapter in connection with Australia. And the Indian subcontinent does not have a single human fossil to record who was making its Middle Paleolithic tools; there is nothing between the archaic-looking braincase from the Narmada River gravels, which is probably over 300,000 years old, and fragmentary modern specimens from sites in Sri Lanka, dating from less than 40,000 years ago.
Work led by the archaeologist Michael Petraglia demonstrated there are Middle Paleolithic tools in Indian sites immediately before and some time after the widespread deposition of the Toba ash about 73,000 years ago, suggesting that whoever those people were, they may have been able to bounce back and repopulate after the apparent destruction wrought by Toba. Petraglia believes they were pr
obably modern humans, perhaps descendants of groups like those known from Skhul and Qafzeh farther west, but if so, their mtDNA and Y-chromosome DNA have not survived today. This is because the M and N mtDNA haplogroups that exist throughout the region are probably younger than 60,000 years, while all Asian Y-DNA is even younger than this. So if these early Indians were modern humans (which is not yet demonstrable), they either became extinct or were largely replaced by later waves of modern human dispersal.
Recent DNA analyses showed just how remarkable was this spread of modern humanity across southern Asia. Study of some 55,000 single-nucleotide polymorphisms (SNPs—individual “spelling mistakes” in the genetic code) in about 2,000 people representing over seventy populations from right across Asia demonstrated that, despite clear physical differences in appearance, skin color, and stature, the inhabitants of east and southeast Asia, including so-called Negrito peoples in the Philippines and Malaysia, are essentially one family of humanity (give or take some Denisovan DNA!) and derive from a single southern migration into the region. Genetic variation within the local populations decreases from south to north in east Asia, so subgroups moved north to found the less diverse populations of northern China, Korea, and Japan. However, the distinctiveness of central Asians suggests that they derived from a separate peopling of that region through the Eurasian Steppes. But groups like the aboriginal inhabitants of Hokkaido Island in Japan—the Ainu—were apparently not included in the analyses, so their origins in an even earlier dispersal of moderns, and a relationship to the first Americans, remains a possibility.
Map showing later human sites.
Map showing later human sites in Europe.
An intriguing and separate study investigated another SNP variant in Asian peoples called EDAR T1540C, and shows how DNA analyses are revolutionizing our understanding of human variation and how quirky some of our “racial” features may turn out to be. Many Asians are characterized by a hollowing on the back surfaces of their upper incisor teeth, called shoveling, since the inside surface resembles a tiny shovel—and a similar shape is also found in Homo erectus and Neanderthals. East Asians are also generally characterized by having straight and coarse black hair. The EDAR gene codes for proteins that are involved in the development of hair, teeth, and other derivatives of our skin and harmful mutations cause a condition called ectodermal dysplasia, where individuals may completely lack hair, nails, sweat glands, and normal teeth. The T1540C variant seems to be related to the production of both shovel-shaped incisors and coarse black hair, and is very common in East Asians, while it is virtually absent in Europeans and Africans. As yet it is unknown what produced the high frequency of this gene in East Asians. Was it chance or was it selection for one aspect—perhaps resistance to a skin disease, a particular kind of tooth strength, or thicker hair to protect against the cold, encourage the attentions of the opposite sex, or discourage the attentions of lice? Whatever the reason, it shows how features that have been considered very important in “racial” and even evolutionary studies may derive from quite unexpected factors—or no factors at all, other than as a by-product of something completely different!
An offshore core from the southern South China Sea records warm conditions and increased summer monsoons between 50,000 and 40,000 years ago, so early moderns who had arrived in the region by then were able to disperse northward under mild rather than glacial conditions—and this was probably the origin of the isolated Tianyuan modern human individual discussed in chapters 3 and 4. These East Asian pioneers were also able to move southward and reached Niah Cave in the Malaysian province of Sarawak, on the island of Borneo, by at least 45,000 years ago. This enormous cave, famous for its birds’ nests which are used for the oriental soup, was partly excavated by Tom and Barbara Harrison more than fifty years ago and produced a wealth of archaeological material of different ages, but the most famous find was the “deep skull” of a modern human. This was controversially radiocarbon dated to about 40,000 years ago from associated charcoal, but many scientists refused to accept the validity of the determination, and it has taken until now for renewed excavations to show that the Harrisons essentially got it right. Moreover, the new work, led by the archaeologist Graeme Barker, showed that these early modern inhabitants of Niah had adapted quickly to the considerable demands of survival in tropical forests, since they were hunting many arboreal species and were processing local plants for their carbohydrates and others for dyes and pigments. However, their stone technology (and apparently their use of other local raw materials) was relatively simple—yet it clearly did the job very well. This reminds us of the important fact that being a modern human is as much about expediency and pragmatism as it is about harpoons, pendants, and cave art.
That is a crucial point to bear in mind as we trace the modern human diaspora toward Australia, because there we will search largely in vain in the earliest archaeological records for the markers of behavioral modernity that we have been discussing so far in this book. Evidence for complex stone or bone technology, structured sites, and symbolic behavior is generally lacking, although, to be fair to the earliest Australians, we already noted that the two 42,000-year-old Mungo fossils may represent the oldest red ocher burial and cremation so far discovered. To get there at all, these early Australians had island-hopped quite rapidly on boats or rafts across many stretches of open sea—the first long-distance seafarers of which we know—assuming, that is, that the ancestors of the Hobbits of Flores had got to that isolated island by accidental rafting rather than purposeful navigation.
The oldest known red ocher burial: Mungo 3 from Australia.
Yet the archaeological record suggests that the earliest Australians lived in small, highly mobile bands and exploited quite a narrow range of plant and animal resources, all of which could be obtained with simple technologies. The stone tools were much more like Middle Paleolithic ones than those we know from the Later Stone Age of Africa or the Upper Paleolithic of western Eurasia, and this led to the earlier suggestion that Australia was first colonized more than 60,000 years ago, before the development of the full suite of “modern” behaviors. However, from the latest dating analyses and genetic studies, it seems difficult to find evidence of colonization much beyond about 45,000 years. Although remembering the apparent simplification of life in Tasmania that followed isolation and decline in numbers, we can see how the same effect could have operated quite severely 50,000 years ago, as small numbers of pioneers survived the hazards of seafaring to reach New Guinea and Australia for the first time, and spread at low density around a vast and challenging continent. Yet in contrast, after 12,000 years ago, when native Tasmanians were apparently suffering a decline in numbers as the Earth warmed up, their mainland fellow Australians were increasing in population density in many regions.
As the archaeologists James O’Connell and Jim Allen pointed out, during the early part of the present interglacial, mainland aborigines underwent their own “Human Revolution,” developing new ways of managing habitats, increasing technological complexity, and engaging in elaborate art and ornamentation, including of their bodies. At the same time there is evidence of a tremendous increase in the number of archaeological sites in regions like the Murray River, so this brings us back to the critical question of population density: was the benefit of increasing numbers the same as we postulated for the later Middle Stone Age of Africa, with greatly increased contacts, exchanges, and symbolic signaling between groups? And was the apparent lack of the signals of modernity in Australia before 12,000 years ago a parallel with the situation in Tasmania after that time, as shrinking and increasingly isolated bands of Tasmanians shed all but the essentials they needed for survival, while indisputably still representing “modern” humans?
This brings us back to the importance of climate, for, as O’Connell and Allen point out, the productivity of Australia was probably much reduced during cooler and more arid phases of the last 50,000 years, while the peak of warmth in the early part
of our present interglacial, plus its relative stability, allowed mainland populations to thrive. And it remains possible that population densities (and hence the potential to express and accumulate signals of “modernity”) fluctuated in Australia between 12,000 and 45,000 years ago. Perhaps the well-watered Willandra Lakes of 40,000 years ago allowed a temporary growth in numbers that catalyzed flashes of the expressions of “modernity” there—such as the exploitation of aquatic resources, red ocher use, and complexity in disposal of the dead.
This gives us an interesting thought-experiment to finish on, using that wonderful episodic memory of ours, before we move on to consider both the past and future of our species in the final chapter. We judge what it is to be human by the standards of our species, as we are the only surviving example available to study in detail. We are large-brained, fully bipedal, small-toothed, and good with technology (give or take an inability to work remote controls or mobile phones properly), and those are features we share to a greater or lesser extent with our extinct relatives in the genus Homo, such as Homo erectus and Homo heidelbergensis. But because people like the Neanderthals did not make it to the present day, we are the only surviving example of a “modern” human, so we look back at our evolution and assess “modernity” in terms of the development of “our” features: a high and rounded skull with a small brow ridge, large parietal lobes in the brain, narrow hips, and a bit of an obsession with religion, sex, and fashion (although not in my case, of course).
Lone Survivors Page 27
