Neanderthals, humans didn’t breed?
British researchers have cast doubt on the theory that modern humans and Neanderthals interbred and instead are more likely to have common ancestry to explain genetic similarities.
The theory of hybridisation, advanced by a number of studies in the last two years, suggests that modern humans, who evolved in Africa, and Neanderthals, who inhabited Europe, had at some point interbred as genetic evidence shows that on average Eurasians and Neanderthals share between 1-4 per cent of their DNA. In contrast, Africans have almost none of the Neanderthal genome. These differences have been explained by hybridisation which occurred as modern humans exited Africa and bred with the Neanderthals.
However, researchers at the University of Cambridge have now suggested that common ancestry, not hybridisation, better explains the average 1-4 per cent DNA that those of European and Asian descent (Eurasians) share with Neanderthals.
Neanderthals and modern humans once shared a common ancestor who is thought to have spanned Africa and Europe about half a million years ago. Just as there are very different populations across Europe today, populations of that common ancestor would not have been completely mixed across continents, but rather closer populations would have been more genetically similar to each other than populations further apart. About 350-300 thousand years ago, the European range and the African range became separated.
The European range evolved into Neanderthal, the African range eventually turned into modern humans. However, because the populations within each continent were not freely mixing, the DNA of the modern human population in Africa that were ancestrally closer to Europe would have retained more of the ancestral DNA (specifically, genetic variants) that is also shared 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. 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,” Dr Andrea Manica, from the University of Cambridge, who led the study said.
The study, published in the journal PNAS, concluded that when modern humans expanded out of Africa 60-70K years ago, they would have brought out that additional genetic similarity with them, making Europeans and Asians more similar to Neanderthals than Africans are on average — undermining the theory that hybridisation, and not common ancestry, explained these differences.
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