It would certainly explain a lot...

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.

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