Researchers have sequenced DNA from the leg bone of a Neanderthal man who died 38,000 years ago and said today it shows the Neanderthals are truly distant relatives of modern humans who interbred rarely, if at all, with our own immediate ancestors.
They estimate that modern humans and Neanderthals split from a common ancestor at least 370,000 years ago, and possibly 500,000 years ago, although we share 99.95 percent of our DNA.
"We see no evidence of mixing 40,000, 30,000 years ago in Europe. We don't exclude it, but see no evidence," Edward Rubin of the US Department of Energy Joint Genome Institute in Walnut Creek, California, who led one study, told reporters.
This conflicts with some evidence from other researchers, including a team who said earlier this month that humans may have inherited a brain gene from Neanderthals. The researchers reported their findings jointly in the journals Nature and Science.
Dr Rubin's team used one method to isolate and sequence part of the Neanderthal's DNA, while another team, led by Svante Paabo of the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, used a separate method to sequence a much larger amount.
Dr Paabo was the first scientist to find and sequence Neanderthal DNA, in 1997, and first suggested that Neanderthals did not mix with modern humans. "I think the sequence data will serve as a DNA time machine that will tell us about biology and aspects that we will never be able to get from their bones and a limited number of associated artifacts," Dr Rubin said.
Neanderthals and modern humans are both descended from Homo erectus, which left Africa and spread around the world about 1.5 million years ago.