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North America was settled in three waves of migration
By Catholic Online (NEWS CONSORTIUM)
July 13th, 2012
Catholic Online (www.catholic.org)
July 13th, 2012
Catholic Online (www.catholic.org)
The largest survey of Native American DNA has reached the conclusion that the New World was settled in three major waves. However, the majority of today's indigenous Americans descended from a single group of migrants that crossed from Asia to Alaska 15,000 years ago or more.
"For years it has been contentious whether the settlement of the Americas occurred by means of a single or multiple migrations from Siberia," co-author Prof Andres Ruiz-Linares from University College London says.
"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."
The team analyzed data from 52 Native American and 17 Siberian groups. More than 300,000 variations in their DNA known as Single Nucleotide Polymorphisms, or SNPs, allowed scientists to examine patterns of genetic similarities and differences between the population groups.
The second and third migrations were only felt in Arctic populations, whose native tongues belong to the Eskimo-Aleut family and in the Canadian Chipewyan who speak a language that belongs to the Na-Dene family.
These populations have inherited most of their genome (the DNA sequence contained in the nuclei of cells) from the earliest migration.
Eskimo-Aleut speakers derive more than 50 percent of their DNA from what the researchers call "First Americans", and the Chipewyan around 90 percent.
"There are at least three deep lineages in Native American populations," co-author David Reich, professor of genetics at Harvard Medical School says.
"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."
Scientists say that this natural bridge appeared during the last Ice Age when sea levels were lower, allowing hunters to trek between the two continents.
A three-stage migration has been proposed before, based on an interpretation of language relationships and physical features of the teeth of Native American groups.
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.
There was little gene flow among Native American groups following this divergence, especially in South America.
The team's analysis was complicated by the influx into the hemisphere of European and African immigrants since 1492 and the 500 years of genetic mixing that followed.
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