America first populated in 'a single wave of migration from Siberia' no more than 23,000 years ago

Analysis of DNA of present day indigineous people throws new light on how our ancestors crossed the Bering land and ice bridge which then connected modern-day Chukotka and Alaska.

A study led by the Centre for GeoGenetics at the University of Copenhagen, asserts that there was one one initial migration from Siberia to America. 

Around 10,000 years later there was a split in these human ancestors into two groups, which anthropologists call  Amerindians (American Indians) and Athabascans (a native Alaskan people).

Previous research had suggested that Amerindian and Athabascan ancestors had crossed the strait independently.

'Our study presents the most comprehensive picture of the genetic prehistory of the Americas to date,' said Maanasa Raghavan, one of the study's lead authors.

'We show that all Native Americans, including the major sub-groups of Amerindians and Athabascans, descend from the same migration wave into the Americas.'

The split into two main branches came about 13,000 years ago, coinciding with glacier melt and the opening of routes into the North American interior, according to researchers.

Another conclusion from the researchers is that given the earliest evidence for the presence of humans in the Americas dates to 15,000 years ago, the first ancestors may have remained in the land bridge of Beringia for about 8,000 years before their final push into the New World.

This is all distinct from later waves which gave rise to the Paleo-Eskimo and Inuit populations, and diversification from the single migration thrust only occurred once the ancient people were in the Americas.  

A second study indicates that some Amazonians descend from forefathers more closely related to the indigenous peoples of Australia, New Guinea and the Andaman Islands than present-day fellow Native Americans.

'Present-day groups in South America have a small but distinct genetic link to Australasians,' co-author Pontus Skoglund of the Harvard Medical School told AFP, speaking about  research published in Nature.

The news agency said this may explain a long-standing riddle: why, if Native Americans came from Eurasia, do some early American skeletons share traits with present-day Australasians?

But how and when this forefather came to the Americas remains 'an open question,' said the study.