Humans mated with Neanderthals 50,000 years ago
Chance discovery of ancient leg bone enables scientists to determine when early humans first mated with extinct cousins, the Neanderthals
An ancient leg bone found on the bank of a Siberian river has helped scientists work out when early humans interbred with the Neanderthals.
A local ivory carver spotted the bone sticking out of sediments while fossil hunting in 2008 along the Irtysh river near the settlement of Usti-Ishim in western Siberia. The bone was identified as a human femur, but researchers have learned little else about the remains until now.
The importance of the find became clear when a team led by Svante Paabo and Janet Kelso at the Max Planck Institute for Evolutionary Anthropology in Leipzig ran a series of tests.
Radiocarbon dating put the remains at 45,000 years old. The team went on to extract DNA from the bone, which allowed them to reconstruct the oldest modern human genome ever.
The genetic material showed the thigh bone belonged to a man who carried about 2 per cent Neanderthal DNA, a similar amount to people from Europe and Asia today. The presence of Neanderthal DNA meant that interbreeding between them and modern humans took place at least 45,000 years ago.
But amid the DNA were more clues to when humans and Neanderthals reproduced. Strands of Neanderthal DNA found in modern humans can act like a biological clock, because they are fragmented more and more with each generation since interbreeding happened. The strands of Neanderthal DNA in the Siberian man were on average three times longer than those seen in people alive today. The scientists calculate that Neanderthals contributed to the man's genetic ancestry somewhere between 7,000 and 13,000 years before he lived.