A new study of over 600 mtDNAs from 20 American and 26 Asian populations is shedding some unique insight on how the Americas were peopled. As you may have been taught, it was thought that the Americas were founded by a not so diverse founding population or two. Before this paper, only about 70 left their genetic print in modern descendants, a very small but effective founder population.
But, there are new results, which were published almost two months ago, that show that there was much more genetic diversity in the founder population than was previously thought. I didn’t catch it until I saw both Razib and Science Daily report on it a couple days ago.
The paper, “Beringian Standstill and Spread of Native American Founders,” was published in the freely accessible PLoS One. Beringia is a fancy way of naming the Bering Land Straight that once connected the north east Asia continent to north west America continent.
One of the more interesting lines of evidence they found from their sequence comparison and their revised phylogenetic map is that the ancestral population literally chilled out in Beringia for a long time. The authors estimate about 15,000 years. That’s long enough so that specific mutations accumulated which separated the New World founder lineages from the Asian sister-clades.
The other more interesting thing that was uncovered was that the founding haplotypes are uniformly distributed across North and South America. They do not show a nested structure from north to south. That means that after what the authors are terming the Beringian standstill and what I’m calling the Beringian chillout, the initial North to South migration was very swift. It was not a gradual diffusion.
And as Razib pointed out in his post, during the last 30,000 years, there was a lot more bouncing back and forth from Northeast Asia and North America. The analysis shows that there was a series of back migrations to Northeast Asia as well as forward migrations to the Americas from Beringia, “more recent bi-directional gene flow between Siberia and the North American Arctic.”
Overall, this study tells us a lot on how people were moving about in the northern hemisphere. But what about oceanic travel, and the recent chicken population genetic similarities? They seem to have made some cultural if not genetic contribution to populations here.
Related sidenote, I like how this study one ups an older PLoS paper, which I reffered to above (the 70 people one). If you want, check out that paper, “On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas.”