Early humans not only lived side-by-side with Neanderthal cave-dwellers, they probably mated with them.
And as a result of these interspecies liaisons, as much as 4 percent of the genes of modern people living outside of Africa originated with Neanderthals, says a report on the mapping of the Neanderthal genome published Thursday in the journal Science.
An international research team used dental drills to tease powder and DNA from the 40,000-year-old bones of three females found in a Croatian cave and then sequenced the DNA. By comparing these ancient genes to those of modern people, the scientists say they've settled the debate over human-Neanderthal sex and are filling in pieces of our evolutionary history.
"The main finding is that there was gene flow from Neanderthals into the genomes of all modern non-Africans," said co-author David Reich, associate professor of genetics at Harvard Medical School in Boston.
Researchers, led by Svante Paabo of the Max Planck Institute for Evolutionary Biology in Leipzig, Germany, compared the Neanderthal genomes to those of five modern humans from Africa, Papua New Guinea, China and France. They found that 1 percent to 4 percent of the genes of Asians and Europeans came from Neanderthals, while the Africans had no genes that were uniquely Neanderthal in origin.
This suggests Neanderthal genes made their way into the population of early humans in the Middle East or northern Africa at least 45,000 years ago, Reich said.
Neanderthals became extinct 30,000 years ago. Or perhaps not.
"The Neanderthals are not totally extinct," Paabo said. "Some of them live on in us."
Blame them for caveman in us