We know that modern humans successfully managed to leave Africa around 65,000 years ago, and that when they did they bumped into other species of human living in different areas. We know that we must have met Neanderthals along the journey, because parts of their DNA still survive in the genome of everyone not of African heritage, meaning that our ancestors interbred with the ancient human species. But that was not the first time that our species tried to leave the African continent, and it turns out, not the first time that we met Neanderthals.
New research has found that interbreeding between the two species happened much earlier than previously thought, around 100,000 years ago. But rather than discovering traces of Neanderthal DNA in modern humans, this new study has looked in the other direction. After analyzing bones from Homo neanderthalensis found in a Siberian cave, the researchers found traces of human DNA. They found that the regions of the genome that were shared between the two species were common in Africans, suggesting that a group of ancient modern humans tried to leave the continent, mated with Neanderthals, and then themselves went extinct.
It now seems that modern humans (red) and Neanderthals (green) mated much earlier than previously thought. Credit: Ilan Gronau
“I was looking to see if I could find regions in the genome where the Neanderthal genome from Siberia has sequences resembling those in humans,” said Martin Kuhlwilm, the co-first author of the paper published in Nature, in a statement. “We know that contemporary non-Africans have traces of Neanderthal in them, so they were not useful to us. So we instead used genomes of contemporary individuals from across Africa to identify mutations which most of them have in common. Some of these mutations occur together in regions of the [Siberian] Neanderthal genome, a sign of interbreeding.”
The team looked at the genetics from a few different Neanderthal remains from across Europe, as well as that of another extinct ancient human species known as the Denisovans. They found that the markers from human DNA were only present in the Neanderthals who lived and died in the Altai Mountains in Siberia, but not in the ones from Spain or Croatia, or in the Denisovans. This implies that when modern humans interbred with Neanderthals 100,000 years ago, likely to have occurred in the Middle East where they both lived at the same time as far back as 120,000 years ago, the decedents migrated to Siberia, but not to the rest of Europe.
The modern human lineage that did the deed with the Neanderthals then died out, one of many failed attempts that our own species made in dispersing from the African continent. The segments of DNA persevered in the Neanderthal bones remain the only evidence that the meeting ever took place. The next time the two species would meet again would be 50,000 years later, when modern humans managed to survive, and it was the Neanderthals who eventually died out.
Main image credit: Erich Ferdinand/Flickr CC BY 2.0