Neanderthals did not interbreed with humans, scientists find

Neanderthals did not interbreed with humans, scientists find
The genetic traits between humans and Neanderthals are more likely from a shared ancestry rather than interbreeding, a British study has suggested.
ByTelegraph Reporters 14 August 2012 • 8:45am
Their analysis contradicts recent studies that found inter-species mating, known as hybridisation, probably occurred.Credit: Photo: ALAMY
Cambridge University researchers concluded that the DNA similarities were unlikely to be the result of human-Neanderthal sex during their 15,000-year coexistence in Europe.
People living outside Africa share as much as four per cent of their DNA with Neanderthals, a cave-dwelling species with muscular short arms and legs and a brain slightly larger than ours.
The Cambridge researchers examined demographic patterns suggesting that humans were far from intimate with the species they displaced in Europe almost 40,000 years ago.
The study into the genomes of the two species, found a common ancestor 500,000 years ago would be enough to account for the shared DNA.
Their analysis, published in the journal Proceedings of the National Academy of Sciences (PNAS), contradicts recent studies that found inter-species mating, known as hybridisation, probably occurred.
Dr Andrea Manica, who led the study, said: "To me the interbreeding question is not whether there was hybridisation but whether there was any hybridisation that affected the subsequent evolution of humans. I think this is very, very unlikely.
"Our work shows clearly 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.
"So, if any hybridisation happened then it would have been minimal and much less than what people are claiming now."
Evidence has shown that Neanderthals were driven into extinction by humans who were more efficient at finding food and multiplied at a faster rate.
A previous study in 2010 suggested that interspecies liaisons near the Middle East resulted in Neanderthal genes first entering humans 70,000 years ago.
Modern non-Africans share more with Neanderthals than Africans, supporting the claim that the mixing occurred when the first early humans left Africa to populate Europe and Asia.
The existence of a 500,000-year-old shared ancestor that predates the origin of Neanderthals provides a better explanation for the genetic mix.
Diversity within this ancestral species meant that northern Africans were more genetically similar to their European counterparts than southern Africans through geographic proximity.
This likeness persisted over time to account for the overlap with the Neanderthal genome we see in modern people today.
Differences between populations can be explained by common ancestry, Dr Manica said.
"The idea is that our African ancestors would not have been a homogeneous, well-mixed population but made of several populations in Africa with some level of differentiation, in the way right now you can tell a northern and southern European from their looks," she said.
“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.
"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.”
Northern Africans would be more similar to Europeans and ancient similarity stayed because there wasn't enough mixing between northern and southern Africans.
Population diversity, known as substructure, cant explain data on the shared genes, said David Reich, a professor of genetics at Harvard Medical School, in Boston who authored the 2010 study.
We have ruled out the possibility that ancient substructure can explain all the evidence of greater relatedness of Neanderthals to non-Africans than to Africans, he added.
Dr Manica said hybridisation between Neanderthals and humans can never be disproved entirely.