Gene study uncovers America’s ancestors

La Trobe bio-archaeologists – in an article just published in the international journal Science – have waded into the highly contentious area of how, when and by whom North and South America was originally populated.

They are Dr Cristina Valdiosera, joint lead-author of a 100-member Scandinavian and US research team, and her colleague Dr Colin Smith.

The genomic study found that, contrary to established theories, populations of so-called 'Paleoamerican relicts' – including the Mexican Pericúes and South American Fuego-Patagonians – are not directly related to modern Australo-Melanesians.

Australo-Melanesians include Papuans, Solomon Islanders and South East Asian hunter-gatherer groups. How they might have interacted with South American settlement has long fascinated archaeologists.

'On the contrary,' says Dr Valdiosera, 'our findings show that supposed Palaeoamerican relicts belong to the same population as present-day Native Americans, and that the distinct cranial morphology of these groups is not a consequence of a distinct migration history.'

Surprise finding

However, in a surprise finding, the study reports that there was a much later gene flow from our part of the world, and that therefore some Native Americans are from groups related to present-day East Asians and Australo-Melanesians.

While the 'genetic signal' for this may be weak, it implies that New World populations were not completely isolated from the Old World after their initial migration.

The study's key finding is that the ancestors of all present-day Native Americans entered the Americas as a single migration wave from Siberia no earlier than 23 thousand years ago.

It seems that this ancestral Native American population was isolated for 8,000-years during which time they remained in the area around Bering Sea, which served as a their land bridge between Russia and Alaska.

Diversified after arrival

After their arrival in the Americas, these ancestral Native Americans eventually diversified into two genetic branches, Amerindian and Athabascan, around 13,000 years ago.

The 'northern' branch was found in northern North America and included both northern Amerindian groups as well as Athabascans. The 'southern' branch included Amerindians from southern North America and Central and South America.

The study, titled Genomic evidence for the Pleistocene and Recent population history of Native Americans, represents the most comprehensive picture of the genetic prehistory of the Americas to date.  

It is based on genomic data from present-day Native American and Siberian populations, which have so far been poorly represented in genetic literature.

It also sequenced ancient samples from across the Americas, from 6,000 to 200 years ago, to trace genetic structure over time.

Media Contact: Ernest Raetz, 0412 261 919

Image: Artist's representation of early Native American ice age landscape, by Sussi Bech.