(AFP) – Jul 11, 2012
PARIS — Native Americans spread out today from Canada to the tip of Chile descended not from one but at least three migrant waves from Siberia between 5,000 and 15,000 years ago, a study said Wednesday.
The finding is controversial among geneticists, archaeologists and linguists -- many of whom have maintained that a single Asian ancestral group populated the Americas.
But the new study, claiming to be the most comprehensive analysis yet of Native American genetics, claims to have found incontrovertible proof that there were three immigration waves -- a theory first put forward in 1986.
Most Native Americans, said the study, descend from a single group known as the "First American" which crossed from Asia via the Beringia land bridge towards the end of the last ice age some 15,000 years ago.
Their modern-day descendants include the Algonquin of Quebec, the Yaghan of Tierra del Fuego and the Kaqchikel Maya of Guatemala.
But two later migrations of people closely related to the Han ethnic Chinese were responsible for creating more groups, according to a paper published in the journal Nature.
"Speakers of Eskimo-Aleut languages from the Arctic inherit almost half their ancestry from a second stream of Asian gene flow, and the Na-Dene-speaking Chipewyan from Canada inherit roughly one-tenth of their ancestry from a third stream," it said.
This indicated interbreeding between later immigrants and the First Americans they encountered.
The second and third waves of migrants may have come to America in boats after the Beringia land bridge disappeared under water at the end of the last ice age, human geneticist Andres Ruiz-Linares of University College London's department of genetics, evolution and environment told AFP.
He coordinated a team of about 60 researchers from around the world who analysed the genetic data of more than 500 invididuals from 52 Native American and 17 Siberian groups, looking for similarities and differences.
They looked at more than 350,000 genetic markers.
The researchers found the most genetic diversity in North America and the most heterogeneous groups in the south -- to where they moved probably as competition for resources increased in the north as more people arrived.
"One of the main results is that natives from the northern parts of the continent would have a more recent Siberian ancestry than other people from the continent," as they mixed with the newcomers, said Ruiz-Linares.
"Native Americans from the lower parts of North America all the way down to Tierra el Fuego originate from the really first settlers of the continent."
For the study, the team had to compensate for the impact of interbreeding with European and African immigrants since Christopher Columbus discovered America in 1492.
Ruiz-Linares said the findings were significant for our understanding of history and how the continent was settled.
"This is part of the issue of how humans evolved and colonised the world," he said.
The study gives genetic backing to the 1986 theory put forward by linguist Joseph Greenberg that the Americas must have been populated in three waves, based on language differences.
His proposition has been widely criticised, but the new study claims to provide evidence allowing science to "reject the view that all present-day Native Americans stem from a single migration wave."
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