NEW YORK (GenomeWeb) – Analysis of ancient DNA has allowed two groups of researchers to trace the movements of ancient human populations that lived in Siberia and those who moved from there into the Americas.
Humans first reached Siberia more than 40,000 years ago during the late Pleistocene, an ice age that occurred from about 126,000 years ago to about 11,700 years ago when Beringia connected Siberia to the Americas.
A pair of studies appearing today in Nature examined genomic data from ancient individuals who lived in these regions to begin to piece together how their populations are related to one another, finding complex interactions.
"[The studies] examine the genetic footprints of past peoples in northeastern Siberia and northern North America, to work out their relationships to modern communities," wrote Arizona State University's Anne Stone in an accompanying commentary that also appeared in Nature.
In the first paper, which focused on the population history of Siberia since the Pleistocene, researchers led by the University of Copenhagen's Eske Willerslev used shotgun sequencing to generate whole-genome data for tooth and other samples from 34 people who lived between 31,600 years ago and 600 years ago at sites across the Arctic region.
From their analyses, the researchers uncovered three major population expansions and replacements during the late Pleistocene and into the early Holocene. A now-extinct population they dubbed Ancient North Siberians first diversified in the region about 38,000 years ago, soon after the split between West Eurasians and East Asians.
"These people were a significant part of human history, they diversified almost at the same time as the ancestors of modern-day Asians and Europeans and it's likely that at one point they occupied large regions of the Northern Hemisphere," Willerslev said in a statement.
But around 18,000 years to 20,000 years ago, people with East Asian ancestry arrived in Siberia and admixed with the descendants of the Ancient North Siberians to form two groups: the Ancient Paleo-Siberians and the First Peoples. East Asians contributed about 75 percent of their DNA to Ancient Paleo-Siberians and 63 percent to the First Peoples, indicating a geographical separation between the groups, according to the researchers
Following the last glacial maximum, the First Peoples move southward and the Ancient Paleo-Siberians were replaced by the Neo-Siberians about 4,000 to 11,000 years ago, the group from which many modern Siberians descend.
Meanwhile, in a separate paper focusing on the peopling of what's now far eastern Russia and North America, researchers led by Stephan Schiffels at the Max Planck Institute for the Science of Human History in Jena, Germany, genotyped 48 individuals who lived between 7,000 years and 200 years ago in Siberia and the American Arctic at 1.24 million SNPs.
The researchers found that much of the genetic ancestry of ancient and modern American Arctic and Chukotkan populations comes from a group they call Paleo-Eskimos, descendants of ancient Siberians who settled in the American Arctic about 5,000 years ago. The ancestors of the Aleutian Islanders and Athabaskans derive their ancestry from admixture of Paleo-Eskimos and First Peoples.
The researchers also found that Paleo-Eskimo ancestry is widespread among modern-day Na-Dene language speakers, which include Athabaskans but also the Tlingit communities of Alaska, northern Canada, and the western and southwestern US, as well as modern-day Eskimo-Aleut speakers.
"For the last seven years, there has been a debate about whether Paleo-Eskimos contributed genetically to people living in North America today; our study resolves this debate and furthermore supports the theory that Paleo-Eskimos spread Na-Dene languages," co-author David Reich of Harvard Medical School said in a statement.
ASU's Stone noted in her commentary that the two papers differed on this point: Willerslev and his colleagues concluded that Ancient Paleo-Siberians contributed to ancestry of Na-Dene speakers through Siberian ancestors instead of through Paleo-Eskimos.
Both studies examined human migration across the Bering Strait and found evidence of migration back into Siberia from the Americas. Copenhagen's Willerslev and his colleagues found, for instance, that individuals from about 2,000-year-old Neo-Eskimo sites harbored 69 percent Ancient Paleo-Siberian and 31 percent Native American ancestry. Similarly, Harvard's Reich and his colleagues found evidence of at least three separate crossings of the Bering Strait.
Stone added that these studies reveal the "complexity of the interactions that occurred within and between Siberian and northern North American populations over time."