by Greg Mayer
The Americas were the last continents to be inhabited, and there has long been controversy about how and when it occurred. There is a general consensus that the earliest Americans arrived from northeastern Asia in the late Quaternary, but the exact peoples involved, the routes taken, when they arrived, and the modes of travel are all much debated. A paper by David Reich and colleagues, in press in Nature, presents evidence on one aspect of the question– did the first inhabitants arrive in one, or in more waves of migration? It has always seemed probable that the Eskimos, culturally and linguistically distinct from the American Indians to the south, and occurring on both sides of Bering Strait, represent a distinct migration, but were the more southern peoples the result of one, two, or more migrations?
Here’s the money quote from Reich et al.’s abstract:
[W]e assembled data from 52 Native American and 17 Siberian groups genotyped at 364,470 single nucleotide polymorphisms. Here we show that Native Americans descend from at least three streams of Asian gene flow. Most descend entirely from a single ancestral population that we call ‘First American’. However, speakers of Eskimo–Aleut languages from the Arctic inherit almost half their ancestry from a second stream of Asian gene flow, and the Na-Dene-speaking Chipewyan from Canada inherit roughly one-tenth of their ancestry from a third stream.
The three migrations thus were by 1) a group the authors call First American, that gave rise to almost all of the Indians of North and South America; 2) the Na-Dene, a group also linguistically identified, that occurs in the US Southwest and a few other places in the US and Canada; and 3) the Eskimo-Aleut, who arrived most recently. These three groups had also been identified by the late linguist Joseph Greenberg (who called the first group “Amerind’).
This is actually pretty much the story as I understood it from the viewpoint of a biologist paying casual attention to the anthropological results. Media accounts (NY Times, BBC) make it sound a bit more novel and controversial than I would have thought. This could be due to my not fully grasping the state of the debates within anthropology (quite possible!), or the hyping that tends to accompany reporting of even the best scientific work.
Reich, D. et al. 2012. Reconstructing Native American population history. Nature, in press.