|16 February 2010
Stone Age Siberians settled in Greenland
A 4,000-year-old Greenland man just entered the scientific debate over the origins of prehistoric populations in the Americas. A nearly complete sequence of nuclear DNA extracted from strands of the long-dead man's hair - the first such sequence obtained from an ancient person - highlights a previously unknown and relatively recent migration of northeastern Asians into the New World about 5,500 years ago, scientists say. Greenland's first known settlers were not Inuit or Native Americans as widely believed, but the direct descendants of Siberians who somehow crossed the Bering Strait to Alaska and then headed east, according to the new report. Because the hair was found in the permafrost, it had been very well preserved; scientists already know from studying the remains of woolly mammoths that hair is a particularly good source of uncontaminated DNA.
An analysis of differences, or mutations, at single base pairs on the ancient Greenlander's nuclear genome indicates that his father's ancestors came from northeastern Siberia, report geneticist Morten Rasmussen of the Natural History Museum of Denmark in Copenhagen and his colleagues in the Feb. 11 Nature. Three modern hunter-gatherer groups in that region - the Nganasans, Koryaks and Chukchis - display a closer genetic link to the Greenland individual than do Native American groups living in cold northern areas of North America, Rasmussen says. A largely complete mitochondrial DNA sequence from the ancient man's hair, extracted by the same researchers in 2008, places his maternal ancestry in northeastern Asia as well.
Danish-led excavations more than 20 years ago unearthed four fragmentary bones and several hair tufts belonging to this ancient man, dubbed Inuk. His remains were found at a site from the Saqqaq culture, the earliest known people to have inhabited Greenland. Saqqaq people lived in Greenland from around 4,750 to 2,500 years ago. One popular hypothesis traces Saqqaq ancestry to Native American groups that had settled Arctic parts of Alaska and Canada by 11,000 years ago.
Inuk's strong genetic ties to Siberian populations raise a different scenario. "We've shown that this ancient individual was not related to Native Americans but derived from an expansion of northeastern Asians into the New World and across to Greenland," says geneticist and study coauthor Eske Willerslev of the University of Copenhagen. The team's new comparative analysis of Inuk's previously sequenced mitochondrial DNA indicates that the Saqqaqs diverged from their closest present-day relatives, Siberian Chukchis, an estimated 5,400 years ago. That calculation implies that ancestral Saqqaqs separated from their Asian relatives shortly before departing for the New World and rapidly traversing that continent to reach Greenland. No land bridge connected Asia to North America at that time, so migrants probably crossed the Bering Strait from what's now Russia to Alaska by boat, Willerslev speculates. As to why the group should head towards Greenland, where it is permanently cold, rather than balmier climes farther south "is a good question," he said. It could be that more favorable lands for settlement were already occupied by rivals, or perhaps they were used to Arctic hardship," said Willerslev. "There's no clear answer to it."
Sources: ScienceNews, Channel 4, Discovery News (10 February 2010), Telegraph.co.uk (11 February 2010)
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