Humans didn't breed with Neanderthals

Posted by Emma Woollacott

Just as we were all getting used to being part-Neanderthal, Cambridge University scientists say we might not be, after all.

Research over the last two years has appeared to indicate that humans interbred with Neanderthals deep in the past, leaving traces of their DNA within us.

But a new study indicates that it's common ancestry, not hybridisation, that best explains the average one-to-four per cent DNA that those of European and Asian descent share with Neanderthals. 

"Our work shows clearly that the patterns currently seen in the Neanderthal genome are not exceptional, and are in line with our expectations of what we would see without hybridisation," says the university's Dr Andrea Manica.

"So, if any hybridisation happened - it's difficult to conclusively prove it never happened - then it would have been minimal and much less than what people are claiming now."

Neanderthals and modern humans share a common ancestor who is thought to have spanned Africa and Europe about half a million years ago.

About 350-300 thousand years ago, though, the two populations became separated. The Europeans evolved into Neanderthals, and the Africans into modern humans.

However, as today, populations wouldn't have been completely mixed across continents: closer populations would have been more genetically similar to each other than those further apart. And because of this, the amount of ancestral DNA shared with Neanderthals would vary.

By examining the different genetic makeup among modern human populations, the scientists attempted to quantify this variation. They simulated a large number of populations representing Africa and Eurasia over the last half-million years, and estimated how much similarity would be expected between a random Neanderthal individual and modern humans in Africa and Eurasia. The resuts were pretty much what we see today.

"Thus, based on common ancestry and geographic differences among populations within each continent, we would predict out of Africa populations to be more similar to Neanderthals than their African counterparts - exactly the patterns that were observed when the Neanderthal genome was sequenced; but this pattern was attributed to hybridisation," says Manica.

"Hopefully, everyone will become more cautious before invoking hybridisation, and start taking into account that ancient populations differed from each other probably as much as modern populations do."