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Oldest known human DNA analyzed: genome narrows down time of mating with Neandertals.

DNA of a 45,000-year-old Siberian man, the oldest modern human genetic material retrieved to date, indicates that he lived a short time after Homo sapiens interbred with Neandertals.

This ancient man belonged to a population that was related to earlier people who left Africa and split into European and Central Asian lines, paleogeneticist Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues report in the Oct. 23 Nature.

The Stone Age man may have belonged to a group that left cutting tools at several Siberian sites dating to as early as 47,000 years ago, the scientists say. No fossils have been found at those sites, raising questions about whether modern humans or Neandertals made the tools.

The ancient man's DNA "shows that there were indeed modern humans in the area of those Siberian sites who could have made stone tools," says study coauthor Janet Kelso, a Max Planck paleogeneticist.

Nine samples of crushed bone from the fossil yielded genetic sequences covering about two-thirds of the man's genome, which allowed for comparisons with the DNA of modern people. The Siberian man displays a genetic link to Andaman Islanders, who are thought to descend from an ancient human migration along the coast of South Asia, the researchers found. The Andaman Islands lie between India and Southeast Asia. The man is also related to East Asians and Native Americans--both considered to be descendants of a northern migration through Asia. The investigators suggest the Siberian individual hailed from a third wave of immigrants to Asia that contributed some genes to ancestors of present-day Asians before dying out.

Comparisons with Neandertal DNA reveal that the man shared 2.3 percent of his genes with Neandertals. Present-day East Asians carry a 1.7 to 2.1 percent genetic contribution from Neandertals, a figure that falls slightly, to between 1.6 and 1.8 percent, in living Europeans.

Based on this new data, modern humans probably interbred with Neandertals between about 50,000 and 60,000 years ago, the team estimates, rather than over a longer period extending further back in the Stone Age (SN: 11/3/12, p. 8). Another recent discovery supports this conclusion. An analysis of DNA from a roughly 36,000-year-old modern human fossil found in Russia dates human-Neandertal interbreeding to about 54,000 years ago, researchers report November 6 in Science.

No signs of interbreeding with Neandertal cousins called Denisovans appear in the Siberian man's DNA. That makes sense, remarks paleogeneticist Morten Rasmussen of Stanford University, since Denisovan genes cluster among present-day Southeast Asians (SN: 9/22/12, p. 5).

Evidence that Neandertal interbreeding began no more than 60,000 years ago supports the idea that a wave of H. sapiens dispersed out of Africa around that time, occasionally mated with Neandertals and passed Neandertal DNA to human populations that led to all non-Africans today, says paleoanthropologist Chris Stringer of the Natural History Museum in London.

Paleogeneticist Mattias Jakobsson of Sweden's Uppsala University finds it intriguing that the Siberian man displays equal relatedness to present-day Asians, a 24,000-year-old Siberian child and a 7,000-year-old Spanish hunter-gatherer (SN: 5/17/14, p. 26). Unlike Paabo's team, Jakobsson suspects the man belonged to a population that has yet to be pinned down but nonetheless helped give rise to current East Asians and Europeans.

Caption: A 45,000-year-old leg bone found in Siberia yielded the oldest known Homo sapiens DNA.
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Title Annotation:HUMANS & SOCIETY
Author:Bower, Bruce
Publication:Science News
Geographic Code:1USA
Date:Nov 29, 2014
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