Modern man and Neanderthals had sex across the species barrier, according to leading geneticist Professor Svante Paabo.
Professor Paabo, who is director of genetics at the renowned Max Planck Institution for Evolutionary Anthropology in Leipzig, made the claim at a conference in the Cold Springs Laboratory in New York.
But Prof Paabo said he was unclear if the couplings had led to children, of if they were capable of producing offspring.
“What I’m really interested in is, did we have children back then and did those children contribute to our variation today?” he said in an article in The Sunday Times.
“I’m sure that they had sex, but did it give offspring that contributed to us? We will be able to answer quite vigorously with the new [Neanderthal genome] sequence.”
The phenomenon is already seen in modern animals such as horses and zebras, and lions and tigers, but resulting offspring have always been infertile.
In recent years, fossils with both Neanderthal and modern human features have been found suggesting the two species interbred but previous scans of Neanderthal genes reveal Neanderthal DNA to have a very different make-up to modern man’s.
It is hoped the new claim will provide an answer to these conflicting discoveries.
Neanderthals were primitive beings that lived alongside modern man 30,000 years ago. The two species coexisted for 10,000- 12,000 years before Neanderthals eventually died out.
Prof Paabo is seeking to prove his theory by examining Neanderthal fossils for traces of modern man’s DNA. But if Neanderthal DNA existed in modern man’s genes, he believes it will have been diluted below detectable levels.
His findings will be published in his analysis of the Neanderthal genome shortly.