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Popular Archaeology Genetic study finds that First Americans were of Asian origin, but arose from multiple migrations of people across Beringia. An international team of researchers, led by Professor Andres Ruiz-Linares from the University College London (UCL) and Professor David Reich of the Harvard Medical School have found that Native American populations originally arose, not from one single migration of people, but at least three. Moreover, their origins can be genetically traced to populations traversing across the ancient Beringia land bridge that existed during the ice ages over 15,000 years ago. "For years it has been contentious whether the settlement of the Americas occurred by means of a single or multiple migrations from Siberia," said Ruiz-Linares. "But our research settles this debate: Native Americans do not stem from a single migration". They found that the majority descended from a single original group of First American migrants, but that at least two subsequent migrations also made important genetic contributions. The team analyzed data samples from 52 Native American and 17 Siberian groups, examining more than 300,000 DNA sequences to examine patterns of genetic similarities and differences between the population groups. The study was complicated by the fact that the Americas experienced an influx of European and African immigrants since 1492, with 500 years of genetic mixing. To address this, the researchers developed a methodology to isolate genomes that were of entirely Native American origin. "We developed a method to peel back this mixture to learn about the relationships among Native Americans before Europeans and Africans arrived," Reich said, "allowing us to study the history of many more Native American populations than we could have done otherwise." Based on the study results, the second and third migrations left their imprint only in Arctic populations that speak Eskimo-Aleut languages and in the Canadian Chipewyan who speak a Na-Dene language. But even these people inherited most of their genetic makeup from the first migration. Eskimo-Aleut speakers, for example, derive more than 50% of their DNA from the first migrants, and the Chipewyan even more, about 90%. This suggests that the two later migrant groups mixed with descendants of the first migrants after they arrived in North America. Said co-author Reich, "the Asian lineage leading to First Americans is the most anciently diverged, whereas the Asian lineages [the second and third migrations] 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." What is more, said Ruiz-Linares, "our study also begins to cast light on patterns of human dispersal within the Americas". They found that people expanded southward along a route that hugged the coast. As they went southward, population groups split off along the way. After the splitting, there was little gene flow among Native American groups, especially in South America. But the dynamics were not always this simple. They found, for example, that the first, Central American Chibchan-speakers have ancestry from both North and South America, suggesting a back-migration from South America, and that the Naukan and coastal Chukchi from north-eastern Siberia carry 'First American' DNA: the Eskimo-Aleut speakers migrated back to Asia, bringing with them the Native American genetic material.
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