The Great Divide

populations from other continental regions (overlapping with
     the findings of the Geno-graphic Project referred to earlier);
there was decreasing genetic diversity as a function of geographic distance from the
     Bering Strait and decreasing genetic similarity to Siberians; the groups most
     similar to Siberians were the Chipewyan population (Na-Dene/Athabaskan) from
     northern Canada and the least similar were those in eastern South America;
there was a relative lack of genetic differentiation between Mesoamerican and Andean
     populations;
they found a scenario in which coastal routes were easier for migrating peoples to
     traverse in comparison with inland routes;
they found some overlap between genetic similarity and linguistic
     classification;
the study showed there was a particular allele (genetic variable)
     ‘private’ to the Americas (i.e., which exists only in the DNA of indigenous Americans), supporting the view that much of
     New World ancestry ‘may derive from a single wave of migration’.
     
    This picture is again overall broadly consistent with the evidence from the
     Genographic Project, and from the analysis of Chukchi DNA , in
     showing a single entry into the Americas, from Siberia, by a group that is roughly 550
     generations old – in other words, who arrived in the New World between, say, (550
     × 30 =) 16,500 years ago and (550 × 20 =) 11,000 years ago, probably using
     a coastal route rather then the inland, inter-glacier route (again, see below). Since
     the study by Sijia Wang and his team, other surveys, not quite so large, have
     nonetheless produced fairly similar results regarding the time of entry of ancient
     peoples into the Americas, but have suggested the entry occurred in two waves not one,
     the first at ~18,700 years ago, the second at ~16,200 years ago. As will
     be seen, this fits in with the linguistic evidence presented below. 7
    It is only fair to emphasise at this point that there are a handful of DNA studies that suggest a much earlier entry of peoples into the
     New World – some at 29,500 years ago, some even at 43,000 years ago. 8 However, the latest and largest studies – the Genographic Project and that by the
     Sijia Wang team – not only agree with each other, broadly speaking, but they also
     agree with the archaeological evidence discovered all across North America, from Alaska
     to New Mexico. Some of this evidence is outlined immediately below but there is a more
     extended discussion in chapter three.
    A second kind of biological evidence comes from the work of Christy Turner,
     at Arizona State University, who is an expert on the evolutionary development of human
     teeth. 9 In particular, Turner has looked at the crowns and roots of
     200,000 teeth of prehistoric Americans, Siberians, Africans and Europeans because (a)
     they show well how populations adapted to different environments, and (b) they are, he
     says, more stable than other evolutionary traits, and tend not to vary so much between
     males and females or between old and young. For our purposes, his work is most
     interesting where it distinguishes between what Turner calls ‘sinodonty’
     and ‘sundadonty’. Sinodont teeth, found mainly among northern Chinese and
     north Asian (Siberian) populations in general, are characterised by ‘incisor
     shovelling’ (scooped-out shapes on the inside of the tooth), double-shovelling
     (scooping out on both sides), single-rooted upper first premolars, and three-rooted
     lower first molars. Turner has found sinodonty in the excavated remains of northern
     Chinese skeletons that go back at least 20,000 years.
    Sinodonty, he finds, is confined to northern Chinese and northern Asian
     populations and in ancient Alaskan and other northern American populations. In
     contrast, such Upper Palaeolithic skeletons as have been found further west – in
     the Lake Baikal area, for example – do not display sinodonty, nor do teeth from
     ancient burials in European Russia. The same is true too of ancient remains found among
     South East Asians. (Turner calls this group ‘sundadonts’ because in
     Palaeolithic times South East Asia, like Beringia, was above sea level, the continental
     shelf there being known as the Sunda Shelf, a phenomenon about which we shall have much
     more to say.) From the spread of sinodonty in northern Asia and North America, Christy
     Turner believes that the first Americans developed from people who migrated slowly
     through