Some New World ancestors came from western Eurasia, not East Asia
Niobe Thompson; inset: Thomas W. Stafford Jr.
An Ice Age skeleton has revealed a genetic link between western Eurasians and Native Americans.
Researchers extracted DNA from a 24,000-year-old arm bone of a young boy found in Mal’ta, near central Siberia’s Lake Baikal. The child may be the oldest modern human to have his genetic portrait painted, and it is entirely different from the picture researchers expected to see.
Part of the boy’s genetic makeup, known as mitochondrial DNA, bears a stamp similar to that of Ice Age and later pre-agriculture European hunter-gatherers. And the boy’s Y chromosome looks more like those of today’s western Eurasians and Native Americans than like East Asians’, Eske Willerslev, a geneticist at the Natural History Museum of Denmark and colleagues report November 20 in Nature.
Native Americans are more related to Asians than to people in other parts of the world, but geneticists have never been able to pinpoint which Asian group is the ancestor of Native Americans, says Ripan Malhi, a molecular anthropologist at the University of Illinois at Urbana-Champaign.
Finding western Asian and European signatures in the boy’s genome surprised Willerslev. “To be completely honest, I thought it was contamination” with modern DNA, he says.
But further analysis showed that the boy’s DNA is purely ancient and that 14 to 38 percent of Native American ancestry may trace to the boy’s people. The Mal’ta people probably met up with East Asians somewhere east of Lake Baikal and interbred with them, giving rise to the ancestors of Native Americans. The researchers aren’t sure when the mixing began or whether it happened in Siberia or somewhere in North America.
Willerslev’s team also reports that DNA from a 17,000-year-old Siberian skeleton from nearby Afontova Gora bears a genetic signature similar to the Mal’ta boy’s, suggesting that his people inhabited Siberia throughout the Ice Age.
That was another surprise. Scientists didn’t think people lived in Siberia during the height of the last great Ice Age, says archaeologist Ted Goebel of Texas A&M University’s Center for the Study of the First Americans. “It was too cold and nasty, too barren and windswept,” he says. Genetic evidence from the Mal’ta and Afontova Gora skeletons indicate the Ice Age Siberians hailed from the western reaches of Asia and spread much farther north and east than previously expected.
The finding could help explain some mysteries surrounding the first people to settle the Americas. Researchers had previously detected hints that modern-day Native Americans and Europeans share distant ancestors. And some ancient American skeletons have traits more characteristic of Europeans and western Asians than of East Asians.
Those pieces of evidence helped spark a theory that Europeans may have crossed the Atlantic more than 10,000 years before Columbus to be among the first people to settle the Americas. That theory is a minority view, with most geneticists, archaeologists and anthropologists agreeing that Native American ancestors came from Asia over a land bridge or along the coast connecting Siberia and Alaska.
The Mal’ta boy’s DNA strengthens the argument that Native American’s ancestors came from northeastern Asia instead of via a transatlantic route, Goebel says.
Although the Mal’ta boy shares DNA with living Eurasians, it would be a mistake to lump him in with modern people, says Connie Mulligan, a molecular anthropologist at the University of Florida in Gainesville. The boy’s genetic profile does not overlap that of any present-day group. “He doesn’t look like anybody modern, which is not surprising because he’s not modern,” she says.
Genetic studies of other ancient skeletons may give a clearer picture of where the boy’s people came from and what happened to them, she says.
“I believe that Native Americans share a significant amount of ancestry with Mal’ta boy,” Mulligan says. “We just don’t know who Mal’ta boy is.”
M. Raghavan et al. Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans. Nature. Published online November 20, 2013. doi:10.1038/nature12736.
T.H. Saey. DNA reveals details of the peopling of the Americas. Science News. Vol. 184, September 21, 2013, p. 16.
B. Bower. Early New World settlers rise in east. Science News. Vol. 157, April 15, 2000, p. 244.