The modern humans probably moved as they always did, expanding into new territory as communities split, not exploring for the sake of adventure. Each new community would have skirmished with the local Neanderthals, who perhaps risked being killed by their fellows if they retreated into the territory owned by neighboring clans and had to hold on to their own territory or face extinction. Year by year, the moderns’ territory expanded and the Neanderthals’ shrank. From the extraordinary length of the process—a border war that took 15,000 years to move across Europe—it is evident that they did not yield easily. But by 30,000 years ago the Neanderthals had disappeared from their final refuges in the Iberian peninsula.355
The Moderns’ Conquest
With the extinction of the Neanderthals, the archaics had been driven from the Eurasian land mass. Only the little Floresians survived, hidden in the forests of their remote island home. Modern humans, in the 20,000 years since their ancestors crossed the Gate of Grief, had occupied much of the world. Their populations, though still sparse, stretched across Eurasia, Sunda, Sahul and Africa.
But this was no imperium on which the sun never set, just a patchwork of tribes with no long range communication and no central authority. Archaeologists have found no towns or villages from this period; people still lived in a state of nature, wholly dependent on hunting and gathering for their existence.
For much of the period during which the exodus from Africa unfolded, from 50,000 to 30,000 years ago, people everywhere may have looked pretty much the same. Everyone outside Africa was descended from the 150 emigrants, who in turn were drawn from the host population in Africa.
The first modern humans were an African species that had suddenly expanded its range. For many millennia people would presumably all have had dark skin, just as do the relict populations of Australia, New Guinea and the Andaman Islands. It seems likely that the first modern humans who reached Europe 45,000 years ago would also have retained black skin and other African features. The Neanderthals, on the other hand, may have lived in northern climates long enough for the melanocortin receptor gene, which controls skin color, to have reverted back to its default state of producing pale skin. Though there exists no direct evidence as to skin color, and the point is only a curiosity, the Neanderthals may have had light skin and their conquerors black. Early Europeans, including the great artists of the Chauvet cave in France, may have retained the dark skin and other badges of their African origin for many thousands of years.
But despite the initial unity of the far-flung human family, regional differences inevitably arose. For archaeologists, the most striking are artistic. There is nothing to match the great painted caves of Europe, even though rock art of the same era is also known from Australia. “We must wonder,” writes the archaeologist Ofer Bar-Yosef in discussing the art of this period, “why western Europe and, in particular, the Franco-Cantabrian region is so different from the rest of the Upper Paleolithic World. It is not the lack of limestone caves or suitable rock surfaces that prevented other social groups or their shamans from leaving behind similar paintings and engravings. Possibly this local flourish had to do with the vagaries and pressures faced by foragers in two major refugia regions at the ends of the inhabited world—western Europe and Australia—where there are claims for rock art of the same general age.”119
There was a significant difference, or the seeds of a difference, between the European and Australian antipodes of the modern human advance from Africa. The Australian and New Guinean branch soon settled into a time warp of perpetual stagnation. They were still living with Paleolithic technology when their European cousins came visiting 45,000 years later. They never broke free from the triple bonds of patrilocal society, nomadic mobility and tribal aggression. For some reason the modern people who reached Europe and the Far East were able to escape this trap and to enter on a phase of steady and continued innovation.
Why these different modes of development occurred is one of the more puzzling questions of prehistory. Historians and social scientists, from the nature of their disciplines, tend to offer purely cultural or environmental explanations for all human differences. From a biologist’s point of view, however, it seems likely that genetic influences would also have been at work, not least because it is hard to prevent an organism from responding genetically to a persistent environmental challenge. When people inhabit polar regions, they adapt genetically to the cold by developing the physique of Eskimos. When people go to live in tropical forests, they may develop pygmy stature, a change that has occurred independently at least three times since the diaspora from the ancestral homeland. Dispersed in small populations from Africa to Australia, from East Asia to Europe, the people of the Upper Paleolithic would have been subject to different evolutionary pressures and to the random effects of genetic drift.
Striking proof of the human tendency to develop local genetic variations has recently emerged from Iceland, whose population has been thoroughly studied by geneticists looking for the roots of disease. Iceland has been settled for just 1,000 years, by settlers from Norway, Britain and Ireland. Yet distinctive genetic variations have already arisen in each of eleven localities in Iceland, according to a test developed by DeCode Genetics, a gene-finding company based in Reykjavik. The reason is that Icelanders, like people throughout the world, have tended to live, marry and die in the same place, and distinctive genetic variations have had time to develop in each locality, even in just 1,000 years. By scanning a person’s genome, DeCode’s researchers can specify where in Iceland that individual’s parents and grandparents came from. The test is based on analyzing the sequence of DNA units at just 40 sites along the genome.120
If a detectable degree of local genetic differentiation has developed in Iceland in a mere 1,000 years, much greater differences are likely to have arisen among populations in the rest of the world, much of which has been settled for 40 times longer and where there have been many social and geographic impediments to the free flow of genes.
Genetic differentiation would certainly have started to act on the human populations of the Upper Paleolithic era. Bruce Lahn, a geneticist at the University of Chicago, has made a striking discovery about the evolution of two genes involved in the construction of the human brain. Each gene has several alternative versions, or alleles, but in each case one specific allele has become much more widespread than the others in certain populations. For an allele to rise to high frequency very quickly is a signature of natural selection hard at work. So presumably each allele conferred some very strong selective advantage.
One of the alleles is an alternative version of a gene known as microcephalin. The allele appeared around 37,000 years ago (though anytime between 60,000 and 14,000 years is possible) and is now carried by some 70% of many populations of Europe and East Asia. The allele is much less common in sub-Saharan Africa, where it is typically carried by from zero to about 25% of the population.
Just some 6,000 years ago a new allele of another brain gene, known as ASPM, appeared in the Middle East or Europe and rapidly rose to prominence, being carried by about 50% of people in these populations. The allele is less common in East Asia and occurs hardly at all in sub-Saharan Africans. 121
What made the two alleles spread so quickly? It seems likely that each conferred some cognitive advantage, perhaps a slight one yet enough for natural selection to work on.
In Lahn’s view, many genes are likely to be involved in constructing the human brain. He has found alleles of two of these genes, both of which happen to be quite common in Europeans and East Asians, but there almost certainly exist alleles of other genes that may be more common in other populations. Each population may therefore have used a different set of alleles to accomplish the same purpose, a well known biological process known as convergent evolution.
Resistance to malaria, for instance, is mediated by protective alleles in a number of genes, but Africans are protected by one set of alleles and Mediterranean peoples by a different, tho
ugh often overlapping, set. The reason is that new alleles arise by mutation, a random process, and each population must make use of whatever alleles it has available. An advantageous allele may spread over time to neighboring populations, but will be more common in the place where it first arose. Lahn believes he is seeing the same phenomenon with alleles that have increased cognitive powers, and has just chanced on two alleles that happen to be common in European and Middle Eastern populations. “It is likely that different populations would have a different make-up of these genes, so it may all come out in the wash,” he says.
Perhaps because of the sensitivity of suggesting that one population might have become genetically more acute than another, several critics asserted that the alleles could have become more common for some reason having nothing to do with the brain, such as conferring resistance to disease. 122 But there is at present no evidence that the microcephalin or ASPM genes do anything other than determine brain size. Some genes do play more than one role, but no other functions have yet been detected for microcephalin or ASPM. Their role in the brain, however, is well established. They first came to light because they are disabled in people with microcephaly, causing the brain to be much smaller than usual, particularly in the cerebral hemispheres that are the site of the brain’s higher cognitive functions.
This strange condition seemed a throwback to the time 2.5 million years ago when the human brain was a third of its present size. In 2004 Lahn established that microcephalin and ASPM, along with several other brain genes, had undergone far more rapid evolution along the line of descent from monkeys to humans than had the counterpart genes in rodents.123 The finding suggested that the brain has grown larger because a succession of new and more powerful versions of genes like microcephalin and ASPM were favored by natural selection. The most recent alleles of microcephalin and ASPM are just a continuation of this process, in Lahn’s view.
A firm conclusion from Lahn’s finding is that human evolution continued after the dispersal of the ancestral population 50,000 years ago, and took different forms in different populations. Much of this evolution may have been convergent, as each population adapted with different alleles to the same challenges. But convergent evolution does not necessarily proceed in lockstep in each separate population. So it could be that the spread of the microcephalin allele some 37,000 years ago expanded the cognitive powers of Caucasian populations and underlay such striking cultural advances as the Aurignacian people’s adeptness at painting caves, while other populations developed such capabilities later.356
When the ancestral human population dispersed across the world 50,000 years ago, evolution set in motion a grand experiment: each population, in its fiercely guarded territory, would develop in its own way. This development would be both cultural, leading to a vast family of different languages, religions and lifestyles, and also genetic, as the members of each society responded to different climates, ecologies and social arrangements of their own making. Isolated on their separate continents, the far flung branches of the human family were to follow different trajectories as each adapted to the strange world that lay beyond the boundaries of their ancestral homeland.
6
STASIS
Nomadic habits, whether over wide plains, or through the dense forests of the tropics, or along the shores of the sea, have in every case been highly detrimental. Whilst observing the barbarous inhabitants of Tierra del Fuego, it struck me that the possession of some property, a fixed abode, and the union of many families under a chief, were the indispensable requisites for civilisation. Such habits almost necessitate the cultivation of the ground; and the first steps in cultivation would probably result, as I have elsewhere shewn, from some such accident as the seeds of a fruit-tree falling on a heap of refuse, and producing an unusually fine variety. The problem, however, of the first advance of savages towards civilisation is at present much too difficult to be solved.
CHARLES DARWIN, THE DESCENT OF MAN
BY 30,000 YEARS AGO, with the Neanderthals ousted from Europe, and Homo erectus confined to a relict population in the forests of Flores, modern humans had replaced the archaic people who had occupied the world outside Africa for more than a million years. But in a sense, nothing had changed. The more modern humans, like the archaics whom they evicted, were foragers who lived off nature’s bounty. They built nothing and left almost nothing behind, save for their stone tools. The newer humans crafted tools of far greater sophistication, including many of bone, and made works of art such as ivory figurines and the decorated caves of France and Spain. But they were still nomads, barred by their mobile way of life from all the material and intellectual possibilities of civilization.
These hunter-gatherers had one more great transition to make before entering the history of civilization. They had first to abandon their nomadic way of life and settle down in fixed communities. Given the great advantages of settled life, presumably settlement was not a previously available option. But why not? What made it so impossible for early people to put a roof over their heads and enjoy the comforts of a fixed abode? What had to happen to make the transition to settlement possible? Why did ancestral humans need to spend 35,000 years wandering in the wilderness before conceiving the benefits of settled life and civilization?
Just as a physical change leading to pygmy form has often evolved in people who live in forests, so a behavioral change may have been necessary for people to abandon the nomadic life they had always known. Settlement may seem a natural choice to us, but it requires a set of wrenching adjustments for hunter-gatherers. They must learn to live with strangers. They must abandon the freedom to move away from danger or from people they don’t get along with. They must yield their firmly egalitarian way of life for a hateful social order of superior and inferior, rife with rules and priests and officials.
Whether or not some genetic change was required to make it happen, the development of settled societies was a transition of profound importance. The interval from 50,000 years ago to 15,000 years ago, when the first settlements appear, is a formative period in human history, even though the precise road to settlement remains obscure.
This pre-settlement period is the subject of the present chapter, and the developments from settlement to agriculture are covered in the next. This division of the human past rests on the assumption that settlement was a decisive step in human evolutionary history and of considerably greater significance than one of its consequences, the expansion of agriculture some 10,000 years ago. Such a demarcation, however, cuts across the usual division recognized by archaeologists. They call the period from about 45,000 to 10,000 years ago the Upper Paleolithic age, based on its characteristic suites of stone tools. These gave way 10,000 years ago to tools of the Neolithic age, which is also equated with the beginning of agriculture.
The shift from the Upper Paleolithic to the Neolithic occurred at the same time as a major climatic transition, the ending of the great Pleistocene ice age that began 1.8 million years ago and the beginning of the Holocene, the warm period that has lasted to the present day. As with the Upper Paleolithic age, the end of the Pleistocene epoch is also set at around 10,000 years ago.
With Africa and Australia already inhabited, the principal developments in human history during the period from 50,000 to 15,000 years ago were those taking place in the Eurasian land mass. Though Europe and East Asia have long had separate and distinctive histories, during the Upper Paleolithic age the peoples of Eurasia followed the same way of life, hunted the same animals across the Eurasian steppe, and endured the same vicissitudes of climate. At the beginning of the Upper Paleolithic, there must have been some intertwining of the populations of west and east Eurasia since both were drawn from a common source, that of the first emigrants who reached India. Women who belong to the mitochondrial lineage known as X are wit nesses of this distant bond. Some of X’s daughters migrated northwest from India and are European; others traveled northeast, crossed Siberia and the land bridge to Alask
a, and are now American Indians.
Only gradually did east and west diverge. The vastness of Eurasia inevitably pushed its Upper Paleolithic people into separate trajectories. This chapter follows the peoples of the west, as they took the slow and difficult steps toward settlement, and the peoples of the east as they domesticated the dog and discovered the Americas.
Upper Paleolithic Transitions
During the Pleistocene, much of northern Europe and northern Asia, or Siberia, was covered in glaciers, and the climate was much drier than now, with frigid deserts skirting the glaciers’ southern edges. Because so much of the oceans’ water was locked up in ice, sea level was more than 200 feet lower for much of the period and the map of the world, could people of the Upper Paleolithic have envisioned any such thing, was very different. Besides the since shrunken continents of Sunda and Sahul, a third land mass, one that is now totally submerged, lay between Siberia and Alaska. Beringia would serve as a broad land bridge to the Americas, but not immediately; for much of the time it was too dry to support vegetation and game, or the travelers who might depend on them.
With their talent for innovation, the people of the Upper Paleolithic quickly learned to live in the frozen north, drawn by the rivers of reindeer that flowed across the vast expanse of the Eurasian tundra. Over the millennia, as the climate and ecological conditions changed, they would switch to mammoth, then to ibex and red deer, and back to reindeer. One culture succeeded another in the archaeological record, but the foraging way of life remained a constant.
As the Pleistocene ice age drew toward its close, a dramatic change occurred in the world’s climate. About 20,000 years ago, in an unparalleled catastrophe known as the Last Glacial Maximum, the glaciers came surging back for a last time, rendering most of northern Europe and Siberia uninhabitable. The world’s population was probably between 1 and 10 million people at the time. A large proportion would have been affected by the sudden chill in climate. The people and animals of Eurasia survived only in southern refuges. Five thousand years later, the glaciers relaxed their hold on the Eurasian continent and retreated, allowing the survivors to move north once more.
Before the Dawn: Recovering the Lost History of Our Ancestors Page 12
