The Journey of Man: A Genetic Odyssey (21 page)
When several microsatellites from M173 chromosomes are examined, the level of variation is consistent with an age of around 30,000 years. Of course, as with any estimate of time, this has a substantial range of error, but the most likely date for the origin of M173 is around 30,000 years ago. This date means that the man who gave rise to the vast majority of western Europeans lived around 30,000 years ago – consistent with a recent African diaspora, and again showing that Neanderthals could not have been direct ancestors of modern Europeans.
Significantly, it is around this time that the Upper Palaeolithic becomes firmly established in Europe – and the Neanderthals disappear. While the Chattelperronian interlude of around 38,000 years ago represented a short experiment with modernity, it is only after 35,000 years ago that we see the inexorable march of modern humans and their toolkits throughout the whole of Europe, as signalled by the appearance of the so-called Aurignacian stone tool industry. By 30,000 years ago the Neanderthals had been nearly eradicated, or perhaps reduced to isolated pockets such as those at Zafarraya in Spain. By 25,000 years ago they had disappeared entirely. The coincidence of the genetic and archaeological dates, as well as the increase in population size implied by the large number of Upper Palaeolithic sites from around 30,000 years ago, suggests that the invading moderns actually
displaced the Neanderthals. But did we actively kill off our distant cousins as we spread into Europe?
A great many theories have attempted to explain the ultimate demise of the Neanderthals. Perhaps the most obvious, given the coincidence of the archaeological and genetic dates for the arrival of modern Europeans, is that they were killed by the newcomers in some sort of hominid genocide. There is, in fact, very little evidence for this. No prehistoric battle sites have been found in France or Spain, and there is little evidence of butchery on the Neanderthal skeletons that have been unearthed. Of course, archaeology may have missed the Neanderthal Waterloo, but on the face of it there is no evidence to suggest inter-species warfare. Rather, it was probably natural selection that did them in.
One of the things that the incoming Upper Palaeolithic Moderns had in their favour was a complex social structure. As we have seen, this probably began as an adaptation to cooperative hunting on the savannahs of east Africa. With their improved toolkits and bands of intelligent, social hunters, modern humans were much more efficient at hunting than the Neanderthals. This can be seen in the Neanderthal remains that have been found, all with extensive evidence of a harsh and physically difficult lifestyle. Most Neanderthals had broken bones, and many had quite extensive injuries that would have made them much less efficient members of the group. What modern humans accomplished with tools and brains, Neanderthals seem to have done with brute force. It was this physically demanding lifestyle that made them relatively short-lived. Few Neanderthals lived to be fifty, and most died in their thirties.
Neanderthals had always had a very dispersed social structure, with a small number of distinct groups, each with its own local tool-making variants. Some anthropologists have even suggested that different Neanderthal groups may have spoken different languages, which would have contributed to the fragmentation of their population. Whether this is true or not, the dispersed, nuclear nature of the
Neanderthal population probably represented an adaptation to the relatively harsh conditions of northern Europe during the last ice age. It allowed them to make use of the resources found over a wide territory, increasing their chances of locating food. It also, inadvertently, probably led to their demise.
Anthropologist Ezra Zubrow has calculated that a reduction in fertility, or an increase in mortality, of 1 per cent would have led to the extinction of the Neanderthals within 1,000 years. This degree of change is entirely consistent with a model in which Neanderthals were gradually excluded from their food resources by incoming, highly efficient Upper Palaeolithic humans. As they became squeezed into smaller and smaller territories, the Neanderthals would have been less likely to obtain the resources they needed in order to survive. Eventually, their numbers reduced through attrition, they may even have had difficulty finding mates. Admittedly this is all conjecture, but it is entirely consistent with the data on the time of arrival of the first Upper Palaeolithic Europeans, the mitochondrial DNA evidence for their population expansion beginning around 30,000 years ago, and the disappearance of the Neanderthals at the same time.
One feature of modern human behaviour that may have played a role in giving them an advantage over the Neanderthals was a by-product of the complex behavioural adaptations of modern humans. What probably began as Upper Palaeolithic hunting skills spilled over into complex social networks. This, coupled with their less physical lifestyles, would have given them a longevity advantage over the Neanderthals. Many Upper Palaeolithic people survived into their fifties, well past reproductive age. This gives us another clue as to why the Neanderthals were replaced: old people are good to have around.
A reliance on teaching and learning, rather than instinct, is one of the things that distinguishes humans from other animals. Most of our early lives are spent learning, and it isn’t until we are well into our twenties that most of us feel that we are in command of sufficient knowledge to be able to synthesize and teach others. The older we get, the more knowledge we accumulate, and the more we can help our offspring to benefit from our experience. Grandparents, like university professors, have ‘been there and done that’ – and, crucially, lived to tell the tale. Having grandparents around also allowed higher
fecundity, since (as any new parent can tell you) they can care for children while younger generations go about their lives. This includes continued childbearing – perhaps allowing that small advantage over Neanderthals that led to their extinction. Anthropologist Kristen Hawkes has suggested that grandmothering – the act of a child being cared for by its grandmother – may have played a substantial role in the population expansion of modern humans. Perhaps the small advantage it gave allowed modern humans to drive the Neanderthals to extinction.
Whatever the causes of their demise, Neanderthals had given up the ghost within a few thousand years of the arrival of modern humans. After 30,000 years ago, the only remains found in Europe are those of fully modern humans – often called Cro-Magnons, after the rock shelter in south-western France where some of the first bones were unearthed in 1868. These early Europeans were much more gracile, and significantly taller, than their Neanderthal neighbours. While Neanderthals were typically only around 165 cm (5 ft 6 in) tall, Cro-Magnons were often over 180 cm (6 feet), with long limbs. To palaeoanthropologists such as Erik Trinkaus, these proportions suggest an origin in a much milder climate. Neanderthals, as long-time residents of the colder regions of Europe, had quite stocky and muscular proportions. The implication is that the Cro-Magnons arrived in Europe from somewhere warmer.
As we saw, lineages belonging to the Middle Eastern clan – which we would expect to find if there had been a straight shot out of Africa to Europe, via the Middle East – are hardly found at all in Europe. M173, our 30,000-year-old marker, has the advantage of being present at very high frequency in the most isolated European populations (including the Celts and the Basques), and its age corresponds roughly to the inferred date of modern human settlement based on archaeology. Other major Y lineages present in Europe are younger than M173, and thus arrived later, or descended from M173 itself. Thus M173 is the likely marker of the first modern Europeans, defining the European
clan. Of course, it is simply the terminal marker in a long line of genealogical descent that traces back to M168 and our African Adam. The penultimate marker, though, actually solves the mystery of where the earliest Europeans came from. This marker, a stepping-stone on the way to M173, is M45 – making Europeans a subset of the central Asian clan.
As we discussed earlier, the steppelands of 30–40,000 years ago stretched across a vast swathe of the Eurasian landmass. To Upper Palaeolithic hunters, this ecosystem would have been a land of plenty, and migration along it would have allowed modern humans to disperse well to the west, into Europe proper, as well as to the east into Korea and China. During this period, the steppe zone extended well into present-day Germany, and may have reached France. We know from bones that have been found in French caves of 30,000 years ago that reindeer – a species adapted to the cold steppe and tundra of northern Eurasia – were common in France around this time. The climate had opened a window into Europe that allowed these central Asian steppe hunters to enter. As we have seen, they soon took over, dominating the region within a few thousand years.
It is likely that their sojourn on the steppes had honed their hunting skills, leading to innovations in technology that gave them a greater advantage over the Neanderthals than would have been possible if they had simply shot straight out of Africa. During the thousands of years they spent on the grasslands of central Asia they almost certainly underwent a period of intense cultural adaptation to this difficult environment. This period took the place of the hundreds of thousands of years of Neanderthal biological adaptation – what had given them their short, stocky frames. As recent migrants from tropical Africa, Upper Palaeolithic humans initially would have been ill equipped for life in the northern hemisphere. The central Asian steppes served as their apprenticeship, in a sense – preparing them for life in the most inhospitable environments on the planet. The caves of western Europe must have seemed relatively benign after the howling winds of the frozen Kazak grasslands.
It is this honing process that may explain why the early Middle Eastern immigrants did not come to dominate Europe. While the mountains and forests of the Balkans would have been a bit of a
barrier for a species adapted to the steppes, some early Middle Eastern immigrants clearly did get through. We can speculate that the low frequency of their Y-chromosome lineages belies a population that was not quite ready for the rigours of life in western Europe – but of course it is impossible to say with certainty. What is clear is that most European men, including me, trace their ancestry back to central Asia within the past 35,000 years. And interestingly, this links us with a small population of Siberian hunters who – just as the last ice age was at its most intense – headed into the frozen tundra of north-eastern Asia.
Zaliv Kresta, the Bay of the Cross, is perched on the eastern edge of Russia, 10,000 km from Moscow. For six months of the year it is frozen solid, a mass of sea ice that isolates the small ex-Soviet settlement of Egvekinot from the rest of the world. The only way to reach it is by a two-hour helicopter flight from Anadyr, the nearest city with regular air connections to the outside world. From Egvekinot, it is a further eight-hour trek on military personnel carriers – armoured, with full tracks – inside the Arctic Circle to reach the reindeer herders living there. It feels like one of the most remote places on earth.
The people who live in this harsh environment, known as the Chukchi, are wonders of adaptation. They have developed a lifestyle that allows them to exist in an environment of unimaginable harshness. When I visited them in November 2001 the temperatures were already plummeting to –50°C at night, and in the depths of winter they can reach –70°. The landscape is an other-worldly tundra, covered in snow and frost from September to June, and there is no edible vegetation. The Chukchi live entirely off of their reindeer and the fish they catch through holes in the icy rivers. They manage to do this with technology that has changed very little over the past few thousand years, sewing their clothes from reindeer skin and sinew, living in tents constructed of hides and wooden poles and migrating with their herds as they search for the succulent lichen tips that provide their only source of nourishment.
Most of us who live in relative comfort in the modern world find it difficult to imagine how humans could exist in these conditions. And yet they do live – and thrive – in a climate that would probably kill most of us. Of all the hominids that have existed over the past few million years, it is only fully modern humans who have been able to live in the harsh Arctic. The conditions are simply too extreme to allow any mental leeway. Natural selection has favoured only those intellectually capable of surviving in this icy evolutionary laboratory.
This is certainly why we see evidence of human occupation in the Asian Arctic only after 20,000 years ago. If modern humans reached southern Siberia around 40,000 years ago, as the genetic and archaeological data suggest, it would take them another 20,000 years before they had developed the cultural adaptations necessary to live in the harsh conditions of the Arctic. It is also possible that population pressures, which may have encouraged a northward migration, were not felt until this time. Whatever the reason, the earliest north-eastern Siberian sites, such as that at Dyuktai, south-east of Yakutsk, and Ushki Lake, in Kamchatka, date from after 20,000 years ago. The people living in Siberia during this time appear to have developed a tool-making culture that was distinct from that of populations living further to the south and west, consistent with their highly adapted lifestyle. They were particularly adept at making microliths, small weapon points, by striking both sides into a symmetrical ‘leaf’ shape. Similar types of stone points have also been found in the earliest excavated American sites, suggesting a direct continuity in culture between Siberia and the Americas.
Anthropologists had assumed for many years that Native Americans and Asians have a common origin. Thomas Jefferson even stated the case in his 1787 book
Notes on the State of Virginia
:
… if the two continents of Asia and America be separated at all, it is by only a narrow strait … and the resemblance between the Indians of America and the Eastern inhabitants of Asia, would induce us to conjecture, that the former are the descendants of the latter, or the latter of the former …