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Oldest known case of Neanderthal-human sex revealed by DNA test

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Traces of DNA found in remains Neanderthal woman show date of first human-Neanderthal couplings is tens of millennia earlier than previously thought

The DNA discovery shows that both Neanderthals and modern humans inherited DNA from prehistoric trysts.
Science editor

Last modified on Wed 14 Feb 2018 16.41 EST

A Neanderthal woman who lived and died in a Siberian cave 50,000 years ago has led researchers to the oldest known case of sex between modern humans and their beefy, thick-browed cousins.

Tests revealed that the female, whose remains were recovered from the Altai mountains on the Russia-Mongolia border, carried traces of DNA from Homo sapiens who appear to have mated with her ancestors 100,000 years ago.

The discovery pushes back - by tens of millennia - the date of the first known couplings between the two groups, and shows that both Neanderthals and modern humans inherited DNA from the prehistoric trysts.

Researchers have known since 2010 that people alive today carry as much as 4% Neanderthal DNA. The genetic legacy, which may affect human immune systems, and the risk of depression and even nicotine addiction, is a smoking gun for interbreeding that took place after modern humans left Africa 60,000 years ago and met up with the Neanderthals.

Dorsal view of the Neanderthal woman’s toe bone.
Dorsal view of the Neanderthal woman’s toe bone. Photograph: Bence Viola

The latest study is the first to ask whether the archaic genes flowed in both directions. It finds that while European Neanderthals bore no traces of modern human DNA, the Altai Neanderthal did. The scientists narrowed the suspects down to early human pioneers who left Africa about 40,000 years before the great migration that saw humans colonise the world. Their adventure was not entirely successful: like the Neanderthals, they appear eventually to have died out.

“An early modern human population left Africa much earlier than had been shown before and met with Neanderthals, possibly those moving from Europe towards the East, some time around 100,000 years ago,” said Sergi Castellano, who led the study at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Writing in the journal, Nature, the researchers describe how they compared complete and partial Neanderthal genomes with those from modern Africans who do not carry Neanderthal DNA. They found no trace of modern human DNA in Neanderthals from Spain or Croatia, but the Altai Neanderthal had strands of DNA that closely matched those of the modern Africans. One strand of modern human DNA found in the Altai Neanderthal involved a gene called FOXP2 which has been linked to language development, but Castellano said it was too early to say whether Neanderthals benefited from the DNA.

Modern humans evolved in Africa about 200,000 years ago. When they left the continent for the north, they encountered Neanderthals who had already settled in Europe and Asia and adapted to the cooler temperatures, lack of sunlight, and different diseases. The interbreeding swapped genes among the two groups.

Scientists have other evidence that Homo sapiens left Africa early but failed to establish themselves beyond the continent. They have recovered 100,000-year-old modern human skeletons from the Skhul and Qafzeh caves in Israel. Meanwhile, a set of 47 modern human teeth found in a cave in southern China was recently dated to at least 80,000 years old.

The excavation of the female Neanderthal’s remains, in the Denisova cave in the Altai Mountains.
The excavation of the female Neanderthal’s remains, in the Denisova cave in the Altai Mountains. Photograph: Bence Viola

“Not only is this the first evidence of modern human DNA entering Neanderthal populations, rather than the reverse process, but this is also a separate and much earlier interbreeding than the one placed at 60,000 years onwards,” said Chris Stringer, head of human origins at the Natural History Museum in London. He said that the interbreeding could have occurred anywhere in southern Asia.

“Does this change the view that the pre-60,000 year old modern human dispersals failed? If both the early modern human groups and the early intermixed Neanderthals went completely extinct, then this was still ultimately a failed expansion,” he added.

Stringer said scientists cannot say whether the sex took place in peaceful relationships, or whether the groups stole each other’s women, or whether abandoned or orphaned babies from one group were adopted by the other.

Adam Siepel, a senior author on the study at Cold Spring Harbor Laboratory in New York, said: “Because children typically stay with their mother, it may suggest that this was a case where a human man mated with a Neanderthal woman, and then she raised the child in her Neanderthal community, into which it was successfully integrated enough to mate itself.

“An alternative, and perhaps slightly less likely, scenario would have a Neanderthal man and a human woman mating and integrating as a family into a Neanderthal community — perhaps by coercion or perhaps not,” he said.