Vol. 328. no. 5979, pp. 680 - 684
DOI: 10.1126/science.328.5979.680
PALEOGENETICS:
Close Encounters of the Prehistoric Kind
Ann Gibbons
The long-awaited sequence of the Neandertal genome suggests that modern humans and Neandertals interbred tens of thousands of years ago, perhaps in the Middle East.
Kissing cousins. A few Neandertals mated with early modern humans and passed on some of their genes to living humans.
CREDIT: TOMISLAV MARICIC
The archaeological record in the caves is ambiguous on that question, and anthropologists have fought bitterly over it. Some claim that the anatomy of fossils shows that Neandertals, our closest cousins, did mate with modern humans, either in the Middle East or in Europe. But others thought modern humans coming out of Africa completely replaced Neandertals with little or no interbreeding. And the genetic evidence from ancient bones showed no sign that Neandertals had swapped genes with our ancestors—until now.
On page 710, an international team of researchers presents their first detailed analysis of the draft sequence of the Neandertal genome, which now includes more than 3 billion nucleotides collected from the bones of three female Neandertals who lived in Croatia more than 38,000 years ago. By comparing this composite Neandertal genome with the complete genomes of five living humans from different parts of the world, the researchers found that both Europeans and Asians share 1% to 4% of their nuclear DNA with Neandertals. But Africans do not. This suggests that early modern humans interbred with Neandertals after moderns left Africa, but before they spread into Asia and Europe. The evidence showinginterbreeding is "incontrovertible," says paleoanthropologist John Hawks of the University of Wisconsin, Madison, who was not involved in the work. "There's no other way you can explain this."
As a result, many people living outside Africa have inherited a small but significant amount of DNA from these extinct humans. "In a sense, the Neandertals are then not altogether extinct," says lead author Svante Pääbo, a paleogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was surprised to find he was part Neandertal. "They live on in some of us."
The team also used the Neandertal DNA like a probe to find the genes that make us modern. Even though the genomes of humans and Neandertals are 99.84% identical, the researchers identified regions that have changed or evolved since our ancestors and Neandertals diverged sometime between 270,000 and 440,000 years ago—their new, slightly younger estimate of the split. So far, the team has detected tantalizing differences in genes involved in metabolism, skin, the skeleton, and the development of cognition, although no one knows yet how these genetic changes affect physiology. "This is a groundbreaking study!" enthuses evolutionary geneticist Hendrik Poinar of McMaster University in Hamilton, Canada. "We can actually discuss an extinct human species—Neandertals—on a genetic level rather than strictly on morphological grounds."
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