HOW THE AMERICAS were first populated thousands of years ago has long been questioned – but new studies of ancient DNA has revealed that Native Americans entered the continent more than 20,000 years ago in one single group.
The data, which came from archaeological studies in Alaska, also discovered a previously unknown Native American population – which have been named ‘Ancient Beringians’.
It is widely accepted that the earliest settlers crossed from what is now Russia into Alaska via an ancient land bridge spanning the Bering Strait. However, issues such as whether there was one founding group or several, and what happened next, have been the subject of extensive debate.
So, how was this new information discovered?
An international team of researchers used DNA from a six-month-old Native American infant, whose remains were found at the Upward Sun River site in Alaska in 2013.
Although the remains dated back 11,500 years, long after people first arrived in the region, researchers found that her genetic information didn’t match either of the two recognised branches of early Native Americans – which are referred to as Northern and Southern.
Instead, she appeared to have belonged to an entirely distinct Native American population – the Ancient Beringians.
Further analyses revealed that the Ancient Beringians were an offshoot of the same ancestor population as the Northern and Southern Native American groups, but that they separated from that population earlier in history.
This timeline allowed the researchers to construct a picture of how and when the continent might have been settled by a common, founding population of ancestral Native Americans, that gradually divided into these different sub-groupings.
“We were able to show that people probably entered Alaska before 20,000 years ago. It’s the first time that we have had first genomic evidence that all Native Americans can be traced back to one source population, via a single, founding migration event,” lead researcher professor Eske Willerslev from the University of Cambridge said.
How does this change our current understanding of Native American history?
The researchers were also to establish that the Ancient Beringian group was more closely related to early Native Americans than their Asian and Eurasian ancestors and then to determine the how, over time, they split into distinct populations.
Until now, the existence of two separate Northern and Southern branches of early Native Americans has divided opinion regarding how the continent was populated.
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The Upward Sun River DNA shows that Ancient Beringians were isolated from the common, ancestral Native American population, both before the Northern and Southern divide, and after the ancestral source population was itself isolated from other groups in Asia.
This means it’s likely there was one wave of migration into the Americas, with all subdivisions to follow, according to researchers.
According to the researchers’ timeline, the ancestral population first emerged as a separate group around 36,000 years ago, probably somewhere in northeast Asia. Constant contact with Asian populations continued until around 25,000 years ago when the gene flow between the two groups ceased.
This was probably due to climate change, according to researchers.
“It therefore probably indicates the point when people first started moving into Alaska,” Willerslev said.
Ancient Beringians themselves then separated from the ancestral group earlier than either the Northern or Southern branches around 20,000 years ago. Genetic contact continued with their Native American cousins, however, until at least the Upward Sun River girl was born around 8,500 years later.
Finally, the researchers established that the Northern and Southern Native American branches only split between 17,000 and 14,000 years ago which, based on the wider evidence, means that they must have already been on the American continent south of the glacial ice.
One significant aspect of this research is that some people have claimed the presence of humans in the Americas dates back earlier – to 30,000 years, 40,000 years, or even more.
“We cannot prove those claims are not true, but what we are saying is that if they are correct, they could not possibly have been the direct ancestors to contemporary Native Americans,” Willerslev said.
The study, Terminal Pleistocene Alaskan genome reveals the first founding population of Native Americans, is published in the Nature journal.
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