October 25, 2013 11:40 am
More than 15,000 years ago the first people came to the Americas, walking across the Bering Strait on a land bridge from Siberia, or maybe sailing east along the coast. These people spread down and through North, Central and South America, with early civilizations like the Clovis people taking root. As the theory goes, early Americans originated from a small group of people that made it over from Asia. But when researchers dig into the genes of some Native American people, unexpected genes, genes with a European heritage, jump out.
The common assumption is that these genes were picked up, mixed into the gene pool from European colonialists. But new preliminary research, reported on by Science Magazine, tells a different story. Some early Americans came not from Asia, it seems, but by way of Europe.
From the complete nuclear genome of a Siberian boy who died 24,000 years ago—the oldest complete genome of a modern human sequenced to date. His DNA shows close ties to those of today’s Native Americans. Yet he apparently descended not from East Asians, but from people who had lived in Europe or western Asia. The finding suggests that about a third of the ancestry of today’s Native Americans can be traced to “western Eurasia,” with the other two-thirds coming from eastern Asia.
The presence of European genes in early Americans has always been confusing, says Nature. But in the new research, says Science, the scientists found that “a portion of the boy’s genome is shared only by today’s Native Americans and no other groups.” Other parts of his genome were tied to Europeans, but the boy had no genetic relationship to modern East Asians.
The researchers think that rather than taking a straight path from East Asia to the New World, the genetic heritage of early Americans was more convoluted:
The team proposes a relatively simple scenario: Before 24,000 years ago, the ancestors of Native Americans and the ancestors of today’s East Asians split into distinct groups. The Mal’ta child represents a population of Native American ancestors who moved into Siberia, probably from Europe or west Asia. Then, sometime after the Mal’ta boy died, this population mixed with East Asians. The new, admixed population eventually made its way to the Americas. Exactly when and where the admixture happened is not clear, Willerslev said. But the deep roots in Europe or west Asia could help explain features of some Paleoamerican skeletons and of Native American DNA today. “The west Eurasian [genetic] signatures that we very often find in today’s Native Americans don’t all come from postcolonial admixture,” Willerslev said in his talk. “Some of them are ancient.”
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