Sunday, February 21, 2010

Science Sunday: Uncle Inuk Upsets The Prehistoric Native American Apple Cart

It has become axiomatic that the more we think we know about the origins of prehistoric populations in the Americas the less we really know. This is because as soon as scientists publish another tome about early Native Americans in clomps a bigfoot like Inuk.
Inuk is a 4,000-year-old man who was a member of the Saqqaq culture, the earliest known people to have inhabited Greenland. The reigning theory is that the Saqqaq were descendants of Native American groups that settled the Arctic regions of Alaska and Canada about 11,000 years ago, but an analysis of four fragmentary bones and several hair tufts belong to this ancient man has blown that theory to smithereens.
An analysis of a nearly complete sequence of nuclear DNA extracted from strands of Inuk's hair -- the first such sequence obtained from an ancient person -- reveals that his father and mother came from northeastern Siberia as a consequence of a previously unknown and relatively recent migration of northeastern Asians into the New World about 5,500 years ago.

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 Saqqaq culture site, 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 in the Arctic regions of Alaska and Canada by 11,000 years ago.

"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," geneticist Eske Willerslev of the University of Copenhagen told ScienceNews reporter Bruce Bower.

Willerslev and fellow scientists conclude that the Saqqaqs diverged from their closest present-day relatives, Siberian Chukchis, about 5,400 years ago. That calculation implies that ancestral Saqqaqs separated from their Asian relatives shortly before departing for the New World and rapidly traversed 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.

The DNA analysis is something of a coup because studies of ancient humans and their ancestors usually face enormous technical challenges. Fossil bones get contaminated with the DNA of those who unearth these finds as well as with fungal and bacterial DNA. Measures to enrich ancient DNA include generating multiple samples of the same genetic sequences and isolating genetic fragments that show no signs of contamination.

Because DNA from hair contains little contamination from fungi or bacteria, the research team focused on Inuk's locks. Frozen conditions following his death also helped to preserve Inuk's DNA and prevent significant contamination. The team generated 20 copies of his genome to confirm that significant contamination had not occurred.

About 84 percent of the DNA extracted from Inuk's hair was his.

"It is amazing how well-preserved this ancient genetic sample is, presumably due to its rather young age and the permafrost in which it was found," said geneticist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

In contrast, 40,000- to 70,000-year-old Neanderthal bones studied by Pääbo’s team have yielded genetic sequences that, because of substantial contamination, generally include no more than 4 percent Neanderthal DNA.

IMAGES (From top): Reconstruction of Inuk's face by Nuka Godfredsen; Saqqaq descendants, Representation of nuclear DNA; Chukchi descendants; Bering Strait; Representation of a Neanderthal.

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