Early modern humans interbred with Neanderthals

All present-day humans who have their roots outside sub-Saharan Africa carry one to three percent of Neanderthal DNA in their genomes. Until now, researchers have 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. However, radiocarbon dating of remains from sites across Europe suggests that modern humans and Neanderthals both lived in Europe for up to 5,000 years and that they may have interbred there, too.

In 2002, a 40,000-year-old jawbone was found by cavers in Oase Cave in south-western Romania and the site was subsequently studied by an international team led by the researchers of the Emil Racovita Institute of Speleology in Romania. Researchers from the Max Planck Institute for Evolutionary Anthropology (Germany), Harvard Medical School (USA), and the Key Laboratory of Vertebrate Evolution and Human Origins in Beijing (China) have now analyzed DNA from this fossil, which is one of the earliest modern-human remains found in Europe. They estimate that five to 11 percent of the genome preserved in the bone derives from a Neanderthal ancestor, including exceptionally large segments of some chromosomes. By estimating how lengths of DNA inherited from an ancestor shorten with each generation, the researchers estimated that the man had a Neanderthal ancestor in the previous four to six generations.

"The data from the jawbone imply that humans mixed with Neanderthals not just in the Middle East but in Europe as well" says Qiaomei Fu, one of the lead researchers of the study. "Interestingly, the Oase individual does not seem to have any direct descendants in Europe today," says David Reich from Harvard Medical School who coordinated the population genetic analyses of the study. "It may be that he was part of an early migration of modern humans to Europe that interacted closely with Neanderthals but eventually became extinct."

"It is such a lucky and unexpected thing to get DNA from a person who was so closely related to a Neanderthal" comments Svante Paabo from the Max Planck Institute for Evolutionary Anthropology who led the study. "I could hardly believe it when we first saw the results." "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," says Mateja Hajdinjak, another key researcher involved in the study.

"When we started the work on Oase site, everything was already pointing to an exceptional discovery," remembers Oana Moldovan, the Romanian researcher who initiated the systematic excavation of the cave in 2003. "But such discoveries require painstaking research to be confirmed," adds 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?"