Anthropologists have dealt a blow to theories that Homo sapiens and Neanderthals interbred, bequeathing humans today with some of the genetic legacy of their mysterious cousins.
Living in genetic isolation, the European range evolved bit by bit into Neanderthals, while the African range eventually became Homo sapiens
Over the past two years, several studies have suggested that H. sapiens got it on with Neanderthals, an enigmatic hominid who lived in parts of Europe, Central Asia and the Middle East for up to 300,000 years but vanished some 30,000 to 40,000 years ago.
Evidence for this comes from fossil DNA, which shows that on average Eurasians and Asians share between one and four per cent of their DNA with Neanderthals but Africans almost none.
But a new study by scientists at Britain’s University of Cambridge says the shared DNA came from a shared ancestor, not from “hybridisation” or reproduction between the two hominid species.
Reporting in the US journal Proceedings of the National Academy of Sciences (PNAS), Andrea Manica and Anders Eriksson at the university’s Evolutionary Ecology Group devised a computer model to simulate a genetic odyssey.
It begins with a common ancestor of Neanderthals and H. sapiens who lived around half a million years ago in parts of Africa and Europe.
Around 300,000-350,000 years ago, the European population and the African population of this hominid became separated.
Living in genetic isolation, the European range evolved bit by bit into Neanderthals, while the African range eventually became H. sapiens, which expanded in waves out of Africa from around 60,000-70,000 years ago.
Communities of H. sapiens that were geographically closer to Europe – possibly in North Africa – retained a relatively larger share of the ancestral genes, according to the theory.
They also became the first colonisers of Eurasia during the progressive “Out of Africa” migration.
This could explain why modern-day Europeans and Asians but not Africans have the tiny bit of genetic similarity 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,” Ms Manica said in a press release.
“So, if any hybridisation occurred – it’s difficult to conclusively prove it never happened – then it would have been minimal and much less than what people are claiming now.”
One of the great questions of anthropology is what happened to the Neanderthals.
Hybridisation would have answered that, at least partly.
By interbreeding with humans, the Neanderthals were not wiped out by H. sapiens or by climate change as some contest. Instead, Neanderthal genes were merged into the genome of the dominant strain of Homo.
In a separate study published in PNAS, scientists led by Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that Neanderthals and H. sapiens split between 400,000 and 800,000 years ago, an earlier date than thought.
The team also calculates that humans split from chimpanzees – our closest primate relative – around seven to eight million years ago, earlier than the six to seven million years ago that is a common estimate.