She probably died in her first year. But the skeleton of an infant girl who lived in Alaska 11,500 years ago has yielded tantalising new evidence for how and when people first colonised America. It reinforces a long-standing idea that the first settlers came from Siberia, across what was then a land bridge.
The girl’s skeleton was recovered in 2013 from the Upward Sun River site in Alaska. It has now yielded enough intact DNA for what remained of her whole genome to be sequenced.
Eske Willerslev of the University of Copenhagen in Denmark and his colleagues compared it with genomes from 167 modern populations, as well as other ancient genomes. The team built a family tree showing how the populations were related. This revealed that the girl was part of the first known lineage from which all Native Americans originated.
“It’s the oldest Native American group we have evidence for so far,” says Willerslev.
The family tree suggests that the girl’s lineage originated in Siberia around 34,000 years ago, at which point they gradually stopped mating with other native Siberians. Around 25,000 years ago, the group acquired new genetic input from proto-Europeans. The resulting people were the ancestors of all today’s Native Americans.
Around the same time, some of these people arrived in Beringia: a large region spanning the north-east corner of what is now Russia and modern Alaska. At the time, sea levels were lower and North America was connected to Asia at this point.
Willerslev calls the girl’s group “Ancient Beringians”. They were the first to reach the Americas. “We’ve established the oldest population was actually in Alaska, not elsewhere, so it’s very strong evidence for the Beringian land-bridge theory,” says Willerslev.
But instead of immediately fanning out into the rest of North America, they stayed in Beringia for thousands of years. They were still there when the little girl lived 11,500 years ago.
By then, other settlers had spilled past the original migrants to reach other areas of North America. These latter settlers would give rise to all modern Native Americans.
Waves of settlers
By 15,000 years ago, the founding Native Americans had diverged into two lineages: northern and southern.
In 2014, Willerslev’s team analysed DNA from a skeleton found in Montana called the “Anzick child”, who lived 12,600 years ago. The child turned out to be closely related to the “new” southern Native American lineage, which had diverged from the earliest Beringian settlers.
This means that, while the baby girl lived more recently than the Anzick child, her lineage is actually older. “She herself is not part of the founding population of America, but part of the founding population that diversified from her original lineage,” says Willerslev.
“The compelling finding is that the genome from 11,500 years ago in Alaska is from a Native American lineage, separate from the present-day lineages of Native Americans before they diversified from each other,” says David Reich of Harvard Medical School in Boston, Massachusetts.
Journal reference: Nature, DOI: 10.1038/nature25173
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