New research has discovered that Native American populations ranging from Canada to the southern tip of Chile all arose from three migrations, with the majority descended almost entirely from one single group of First American migrants that crossed from Asia into America across the then existing Beringia land bridge, more than 15,000 years ago.
The researchers studied variations in Native American DNA structures and found that while most of the Native American populations spawned from one single migration, two subsequent migrations also made contributions.
“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.”
This is easily the most comprehensive survey of its kind, taking data from 52 Native American groups and 17 Siberian groups and studying more than 300,000 specific DNA sequence variations called Single Nucleotide Polymorphisms to examine the patterns of genetic similarities between the two population groups.
The subsequent migrations left an impact only in Arctic populations that now speak Eskimo-Aleut languages and in the Canadian Chipewyan who speak a Na-Dene language. Even so, Eskimo-Aleut speakers derive more than 50% of their DNA from First Americans, and the Chipewyan around 90%. This can be explained by the simple fact that the two later migrations from Asia mixed with the First Americans they encountered upon arrival.
“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 research team discovered that one reaching the Americas, the migratory groups spread southward along a route that hugged the coast, and populations split off from that route as they moved south. Once this divergence took place, there was very little gene flow among Native American groups. This was especially the case in South America.
However, there are two wonderfully exciting variations to this rule;
- The Central American Chibchan-speakers have ancestry that links them to both North and South America. This reflects “back-migration” from South America.
- Naukan and coastal Chukchi from north-eastern Siberia carry ‘First American’ DNA, which means that at some point, Eskimo-Aleut speakers migrated back to Asia, bringing with them their new Native American genes.
“The study of Native American populations is technically very challenging because of the widespread occurrence of European and African mixture in Native American groups,” said Professor Ruiz-Linares.
“We developed a method to peel back this mixture to learn about the relationships among Native Americans before Europeans and Africans arrived,” Professor Reich said, “allowing us to study the history of many more Native American populations than we could have done otherwise.”
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