One of the oldest known bones from a modern human in Europe contains around 6 to 9 percent Neanderthal DNA, more than any other human sequenced to date, according to genetic analysis by an international research team.
The findings imply that some of the first modern humans who came to Europe interbred with local Neanderthals.
All present-day humans who have their roots outside sub-Saharan Africa carry 1 to 3 percent Neanderthal DNA in their genomes. Until now, researchers thought it most likely that early humans coming from Africa mixed with Neanderthals in the Middle East around 50,000 to 60,000 years ago, before spreading into Asia, Europe and the rest of the world. Neanderthals then became extinct about 40,000 years ago.
However, radiocarbon dating of remains from sites across Europe suggested that modern humans and Neanderthals lived alongside one another in Europe for several thousand years, suggesting that they could have interbred there as well.
The amount of Neanderthal DNA measured in the current study, from the jawbone of a man who lived somewhere between 37,000 and 42,000 years ago in Romania, suggests that the man had Neanderthals in his family tree as recently as four to six generations earlier.
“The data from the jawbone imply that humans mixed with Neanderthals not just in the Middle East but in Europe as well,” said Qiaomei Fu, a research fellow in genetics at Harvard Medical School and co-first author of the study.
The findings were published June 22 in Nature.
The jawbone was found in 2002 in Oase Cave in southwestern Romania. An international team led by researchers from the “Emil Racoviţă” Institute of Speleology in Romania subsequently came to study the site. Researchers from HMS, the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and the Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences in Beijing, then analyzed DNA from the jawbone.
The researchers estimated how recently the man’s ancestors had interbred with Neanderthals based on calculations of how lengths of DNA inherited from an ancestor shorten with each generation. They also found that “exceptionally large” segments of some of the man’s chromosomes were of Neanderthal origin.
“It is such a lucky and unexpected thing to get DNA from a person who was so closely related to a Neanderthal,” said Svante Pääbo of the Max Planck Institute, who led the study. “I could hardly believe it when we first saw the results.”
“One of the most exciting things about the Oase individual is that he is from a population that did not contribute much or at all to Europeans today,” said David Reich, HMS professor of genetics, who led the study’s analyses of population history. “The genetic data show that he was a member of a pioneer population of modern humans who got to Europe early, mixed with local Neanderthals and then was displaced by later migrations.”
“We hope that DNA from other human fossils that predate the extinction of Neanderthals will help reconstruct the interactions between Neanderthals and modern humans in even more detail,” said Mateja Hajdinjak, a graduate student at the Max Planck Institute and co-first author of the study.
“When we started the work on Oase site, everything was already pointing to an exceptional discovery,” said Oana Moldovan, the Romanian researcher who initiated the systematic excavation of the cave in 2003.
“But such discoveries require painstaking research to be confirmed,” added Silviu Constantin, her colleague who worked on dating of the site. “We have previously shown that Oase is indeed the oldest modern human in Europe known so far, and now this research confirms that the individual had a Neanderthal ancestor. What more could we wish for?”