"Modern" European humans and Neanderthals may have interbred in the comparatively recent past, suggest Anthroboffins, with the latter contributing a much higher percentage of their stocky DNA to today's humanity than had been thought.
Detailed in a letter published in Nature, titled An early modern human from Romania with a recent Neanderthal ancestor, scientists from Harvard have found a much more prominent link between modern humans and Neanderthals than originally believed.
The boffins analysed the trace DNA that could be obtained from the specimen of a "modern human" found in Peștera cu Oase (meaning the cave with the bones) in Romania, dating from 35,000-40,000 BCE (Before Common Era).
They found that, while Neanderthals are thought to have disappeared in Europe approximately 39,000-41,000 years ago, and are considered to have "contributed 1-3 per cent of the DNA of present-day people in Eurasia", the genome of the individual found in Peștera cu Oase is derived from Neanderthals on the order of 6-9 per cent, so "more than any other modern human sequenced to date".
Three chromosomal segments of Neanderthal ancestry are over 50 centimorgans in size, indicating that this individual had a Neanderthal ancestor as recently as four to six generations back.
However, the Oase individual does not share more alleles with later Europeans than with East Asians, suggesting that the Oase population did not contribute substantially to later humans in Europe.
"It's an incredibly unexpected thing," said Prof David Reich, a co-author of the paper from the Harvard Medical School. "In the last few years, we've documented interbreeding between Neanderthals and modern humans, but we never thought we'd be so lucky to find someone so close to that event."
The Peștera cu Oase individual's genetic information was retrieved from a fossilised jawbone, found in the cave back in 2002.
Through analysis of how the lengths of DNA segments, identifiable to distinct ancestors, shorten with each generation, the researchers used this information to estimate a picture of the kind of relationship that existed between early modern humans and Neanderthals.
"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, the study's first author.
"Interestingly, the Oase individual does not seem to have any direct descendants in Europe today," noted Reich, 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."
"When we started the work on Oase site, everything was already pointing to an exceptional discovery," Oana Moldovan, the Romanian researcher who initiated the systematic excavation of the cave in 2003, said.
"We have previously shown that Oase is indeed the oldest modern human in Europe known so far," said Silviu Constantin, a colleague of Moldovan who worked on dating of the site. "Now this research confirms that the individual had a Neanderthal ancestor. What more could we wish for?" ®