The Great Divide

eastern Mongolia, the Upper Lena Basin, eastern Siberia, and from there across
     the Bering Strait into Alaska.
    Still further biological support for this scenario is found in the fact that
     the infants of some American indigenous tribes are born with the so-called
     ‘Mongol spot’, a bluish birthmark at the base of the spine that soon
     disappears and is also found among children in Tibet and Mongolia. 10
    Putting all this genetic evidence together, therefore, we may say that the
     early people from whom virtually all Native Americans alive today are descended, arrived
     in the Americas – very roughly speaking – about 16,500–15,000 years
     ago, from somewhere in north-eastern Asia, the area that is now Siberia, just possibly
     as far south as Mongolia. There may have been small groups of people who found their way
     to the Americas earlier than that but their effect on later populations was negligible.
     And there may have been later migrations, the evidence for which will be considered
     shortly.
    Timothy Flannery makes the point that, although the Aleuts and Inuits in
     Alaska share many cultural features with north-east Asians (including a form of Eskimo
     spoken on the Kamchatka Peninsula in Russia, and a variety of acupuncture practised in
     the Aleutian Islands similar to that used in China), there is very little evidence of
     people or ideas going back to Asia from the Americas. The only genetic study that
     throws any light on this is that produced by Nicholas Ray and colleagues who cautiously
     concluded that some Native Americans crossed back into Asia 390 generations (or 9,750
     years) ago. A well-publicised study of the only surviving Yeneseian-speakers, the Kets
     in central Siberia (several thousand miles from the Bering Strait), showed a linguistic
     link between the Yeneseian and Na-Dene languages but, genetically, the Kets were very
     similar to the other Siberian groups around them, and not at all related to the Na-Dene
     speakers in North America. At the moment there is no satisfactory explanation for this
     anomaly. But we may conclude, therefore, that the main migration across the Bering Land
     Bridge went from Siberia to Alaska and occurred – crucially – towards the
     end of the Ice Age. 11
     
    There is one other piece of genetic evidence we need to consider
     before moving on. This is the work of Bruce Lahn, at the University of Chicago, who has
     discovered two genes which are involved in the construction and enlargement of the human
     brain. Each gene has several alternative forms, or alleles, but in each case one version
     has become far more common than others among certain populations. This disparity must
     mean that the effect of this allele was of great evolutionary significance, providing a
     selective advantage. One of the alleles is a version of a gene known as microcephalin.
     This first appeared some 37,000 years ago and is carried by 70 per cent of populations
     in Europe and Asia but is much less common in sub-Saharan populations, where it is
     carried by between 0 and 25 per cent of people. The second allele is known as ASPM (for Abnormal Spindle-like Microcephaly-associated) and
     appeared and then spread rapidly in the Middle East and Europe around 6,000 years ago.
     This allele is absent in sub-Saharan Africa and only weakly represented in East Asia. 12
    For these two alleles to have spread so quickly, they must each have
     conferred some cognitive advantage. For obvious reasons this is material that should be
     interpreted with the utmost caution, as Bruce Lahn himself has counselled. There is at
     the moment no evidence these alleles are associated with increased intelligence; set
     alongside the other results mentioned above, however, these discoveries may have two
     implications that concern us. First, so far as the mutation that occurred around 37,000
     years ago is concerned, one might ask whether this allele had anything to do with the
     ‘cultural explosion’ that occurred in the palaeontological record
     beginning around 33,000 years ago, with the notable florescence of cave art in certain
     areas of Europe. And, by the same token, was the mutation that occurred some
     6,000–5,000 years ago in any way related to the development of civilisation that
     appeared roughly 5,500 years ago? Are we seeing here a link between genes and culture
     that has not been suspected before, because such results were not available?
    If so, then the second implication