Sweeping DNA studies indicate the first inhabitants of North America traveled from Asia in at least three waves, not one main migration as originally thought.
Researchers writing in the journal Nature said migrants began crossing a land bridge over what is now the Bering Strait from Siberia more than 15,000 years ago.
"We have various lines of evidence that there was more than one migration," Dr. Andres Ruiz-Linares, a professor of human genetics at University College London and senior author of the report, told the Los Angeles Times.
Ruiz-Linares and colleagues around the world analyzed blood samples from modern-day Native Americans and Inuit, along with other indigenous populations extending throughout Greenland and North and Central America and into South America. They found that most of the groups they studied did indeed come from one ancestral group.
However, they found that the Eskimo-Aleut populations of the Arctic got nearly half of their DNA from a second ancestral group, and the Na-Dene-speaking Chipewyans inherited 10 percent of their DNA from a third ancestral group.
Ruiz-Linares said the findings bolster a theory proposed in 1986 by Joseph Greenberg, a Stanford University anthropological linguist who said language similarities suggest the first colonists came to the Americas in three distinct migrations.
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