Humans and Neanderthals – long-term lovers

We know the Neanderthals interbred with humans – their DNA lives on in us. But a new study shows the affair began 100,000 years ago, much earlier than we thought. Belinda Smith reports.

More than 100,000 years ago, modern humans ventured out of Africa and proceeded to bump uglies with Neanderthals as they went. – IVAN HEREDIA / CSIC

Modern humans' love affair with Neanderthals stretches back far longer than we thought, with a genetic analysis showing they interbred around 100,000 years ago.

An international team led by Martin Kuhlwilm from the Max Planck Institute for Evolutionary Anthropology in Germany found traces of human DNA mixed in 100,000-year-old Neanderthal fossils found in Siberian mountains.

Previously, anthropologists thought the two species first met when modern humans, Homo sapiens, left Africa 65,000 years ago. This new study suggests some modern humans made the move early, encountered – and had sex with – Neanderthals, then went extinct.

The analysis was published in Nature.

"We now find evidence for a modern human contribution to the Neanderthal genome," says Sergi Castellano, senior author of the paper. "This is likely the result of much earlier interbreeding."

The researchers analysed DNA from the fossilised remains of three Neanderthals from the Altai mountains in Siberia, Vindija Cave in northern Croatia and Sidrón Cave in northern Spain.

They also probed the DNA of another early and now extinct human – a Denisovan – also from the Altai mountains. Denisovans and Neanderthals shared a common ancestor 381,000 to 473,000 years ago.

But when they studied the Altai Neanderthal genome, they saw it contained telltale H. sapien genes.

The only way modern human DNA could've found its way into the Neanderthal was, well, sex between the species, 100,000 years ago.

Scenario of interbreeding between modern humans and Neanderthals: Neanderthal DNA in present-day humans outside Africa originates from interbreeding that occurred 47,000 - 65,000 years ago (green arrow). Modern human DNA in Neanderthals is likely a consequence of earlier contact between the two groups roughly 100,000 years ago (red arrow). – Ilan Gronau

The Denisovan, on the other hand, didn't contain any H. sapiens genetic material, nor did the Croatian or Spanish Neanderthals.

This "gene flow" fits with recent evidence that modern humans made their way to southern China as early as 120,000 years ago.

These early movers may have had more opportunity to get it on with other hominins than their relatives, who waited 50,000 years before spreading from Africa, the researchers write.

Further reading:
The Neanderthals live on in us
Depressed? Blame it on the Neanderthals

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