Scientists have found that Native American populations -- from Canada to the southern tip of Chile -- arose from at least three migrations, with the majority descended entirely from a single group of First American migrants that crossed over through Beringia, a land bridge between Asia and America that existed during the ice ages, more than 15,000 years ago.
By studying variations in Native American DNA sequences, the international team found that while most of the Native American populations arose from the first migration, two subsequent migrations also made important genetic contributions. The paper is published in the journal Nature July 11.
"For years it has been contentious whether the settlement of the Americas occurred by means of a single or multiple migrations from Siberia," said Professor Andres Ruiz-Linares (UCL Genetics, Evolution and Environment), who coordinated the study. "But our research settles this debate: Native Americans do not stem from a single migration. Our study also begins to cast light on patterns of human dispersal within the Americas."
In the most comprehensive survey of genetic diversity in Native Americans so far, the team took data from 52 Native American and 17 Siberian groups, studying more than 300,000 specific DNA sequence variations called Single Nucleotide Polymorphisms to examine patterns of genetic similarities and differences between the population groups.
The second and third migrations have left an impact only in Arctic populations that speak Eskimo-Aleut languages and in the Canadian Chipewyan who speak a Na-Dene language. However, even these populations have inherited most of their genome from the First American migration. Eskimo-Aleut speakers derive more than 50% of their DNA from First Americans, and the Chipewyan around 90%. This reflects the fact that these two later streams of Asian migration mixed with the First Americans they encountered after they arrived in North America.
"There are at least three deep lineages in Native American populations," said co-author David Reich, Professor of genetics at Harvard Medical School. "The Asian lineage leading to First Americans is the most anciently diverged, whereas the Asian lineages that contributed some of the DNA to Eskimo-Aleut speakers and the Na-Dene-speaking Chipewyan from Canada are more closely related to present-day East Asian populations."
The team also found that once in the Americas, people expanded southward along a route that hugged the coast with populations splitting off along the way. After divergence, there was little gene flow among Native American groups, especially in South America.