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.
"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.
