North and South America were totally empty of people until the first arrivals from Siberia crossed a land bridge into Alaska, spreading in a few thousand years to the tip of South America. The genetic study may help settle a debate between a long-held view that the populating of the continents came as one event instead of the more recently supported notion, backed by this study in the journal Nature, that the migration happened in three distinct waves.As far back as I can remember in graduate school, I was taught that there were at least two, probably three migrations. The two that I remember studying were from the Lena River Basin in Siberia and the Amur River basin, on the border of Russia and China. There were probably more than that, as there are some Native American populations that have gene fixation for certain blood types, a situation that would only occur in a drift/founder effect situation. I remember Dick Jantz teaching us this twenty years ago, at UT.
"Our study makes clear that mixing of these three ancient populations is the story of Native American arrival," says geneticist David Reich of Harvard Medical School, lead author of the study.
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