Siberians came to North American Arctic in two waves

DNA recasts an ancient mystery of how one far northern culture replaced another

2:31pm, August 28, 2014

SECOND COMING  Inhabitants of an Alaskan island made wooden dolls such as this between 400 and 500 years ago. These people may have been part of a second wave of migration to the North American Arctic. 

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North America’s Arctic regions were first settled around 5,000 years ago by people from Siberia who eventually created a New World culture that lasted for nearly 4,000 years before suddenly disappearing, a new genetic study suggests.

This founding Arctic culture vanished either shortly before or after the arrival of a second, genetically distinct crowd of Siberians. That later band of immigrants spread their Thule culture across Alaska, northern Canada and Greenland and served as the ancestors of present-day Inuits, says a team led by paleogeneticists Maanasa Raghavan and Eske Willerslev, both of the University of Copenhagen.

Neither the Thule nor the earlier Arctic colonists, who created tools and figurines typical of what’s known as Dorset culture by around 3,000 years ago, display a genetic connection to current Native American groups to the south, the scientists report in the Aug. 29 Science.

Instead, Native Americans descended from another group of Siberians that migrated to North America across a land bridge at least 12,000 years ago, the investigators propose.

While their North American populations may have overlapped for only a handful of generations, members of the Dorset and Thule cultures did share genetic similarities that point to a common, founding population in Siberia that existed before anyone reached Arctic North America, Raghavan says.

New genetic evidence also challenges a prevailing view that a remnant population of Dorset descendants survived into the early 20th century, until they died from a disease introduced by European whalers. The Sadlermiut people, inhabitants of two islands in Canada’s Hudson Bay who perished along with their non-Inuit-like culture in 1903, display evidence only of Inuit ancestry, Raghavan says. Sadlermiut culture developed over generations of living in isolation from other Inuit groups, in her view.

The real mystery is why the Dorset disappeared so completely after they and their New World ancestors had survived successfully in the Eastern Arctic for around 3,500 years, writes anthropologist Robert Park of the University of Waterloo in Canada, in a comment published in the same Science.

Radiocarbon dates from ancient campsites indicate that Dorset and Thule peoples coexisted in the New World for as many as 150 years, says anthropologist and study coauthor William Fitzhugh of the Smithsonian Institution in Washington, D.C. Dorset people were no match for bow-and-arrow-equipped members of large, well-organized Thule communities capable of hunting walruses and large whales, Fitzhugh holds. Dorset folk were either pushed out or annihilated by the newcomers, he suspects.

Park disagrees. No evidence exists that Dorset people uprooted entire villages or retreated to less desirable locations near the end of their run, he told Science News. Radiocarbon dates in the Arctic may be off by decades or centuries, he adds. Dorset people were gone before the Thule arrived, Park suspects, for unknown reasons.

Willerslev’s team extracted mitochondrial DNA from preserved bones, teeth and hair of 154 ancient individuals excavated in Arctic Siberia, Alaska, Canada and Greenland. Data from complete mitochondrial genomes came from 26 ancient samples. Comparisons of mitochondrial DNA sequences allow researchers to trace people’s maternal ancestry.

Ancient samples included mitochondrial DNA previously obtained from 4,000-year-old hairs from a Greenland man (SN: 3/13/10, p. 5) and the 24,000-year-old arm bone of a Siberian boy (SN: 12/28/13, p. 16).

The researchers also analyzed nearly complete mitochondrial genomes from seven present-day Arctic residents: two Native Americans in western Canada, an Inuit in Greenland, an Aleutian Islander and two Siberians.

Ancient Thule individuals showed no genetic relationship to 34 modern Scandinavians from southern Greenland, a finding that argues against mating between the Thule and Vikings who reached Greenland around 1,000 years ago.

Editor's Note: This story was updated September 16, 2014, to make clear that the statement from Robert Park was a paraphrase, not a direct quote from the Science commentary.

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