Genetics Predicts the End of Neanderthals: They Didn’t Die Out, We Assimilated Them | Science

In 2010, a Swedish geneticist who had spent his youth obsessed with reconstructing the genetic material of an Egyptian mummy achieved much greater success. That same year, Svante Pääbo uncovered the first genome of a Neanderthal, the closest relative to our species, and confirmed that we had sex and children with them tens of thousands of years ago. It was a cataclysm in human evolutionary history, and its effects are still felt by most of the world’s population, who still carry a small percentage of Neanderthal DNA in every cell. In 2022, his lab colleagues threw Pääbo into a pond to celebrate winning the Nobel Prize in Medicine for his discoveries.

A new ability to extract and read DNA from fossils has provided evidence of how and where sexual encounters took place between the human species native to Europe, the Neanderthals, and us, Homo sapiensoriginating from Africa. Until now, science has focused on the influence of Neanderthal genes on our species, such as that Neanderthals and Denisovans, another human species discovered by Pääbo, gave us the necessary genes needed to live in the highest regions of the planet, and others that strengthened our immune system in the past but made it more vulnerable in the present. The biggest mystery remains why, if we were so compatible, the Neanderthals disappeared forever 40,000 years ago, leaving us, sapiens, the only human species on planet Earth.

A study is published this Thursday that turns that story around and asks what influence sapiens DNA had on Neanderthals, and whether we somehow contributed to their extinction. The results he publishes The scienceA guide to the world’s best science, it reveals unknown chapters of this history.

“Our data support the idea that the most important factor in the extinction of Neanderthals is probably that they were simply absorbed by sapiens,” molecular biologist Liming Li of Princeton University in the US and the first author of the study explains to the newspaper.

The researchers analyzed the only three surviving Neanderthal genomes: that of a man found in Vindija, Croatia, who lived about 52,000 years ago, another found in Chagyrskaya, in the Altai Mountains of Siberia, Russia, about 80,000 years ago, and a third Neanderthal from Denisova Cave, also in the Altai Mountains, who lived about 120,000 years ago. They compared their genomes with those of 2,000 modern sapiens to calculate how much genetic material we passed on to Neanderthals and when it happened.

The work confirms that the first and largest encounter between the two species occurred much earlier than previously thought, around 200,000 years ago. Groups Homo sapiens After leaving Africa, they arrived in Europe and had sex and children with Neanderthals, to whom they passed on up to 10% of their genome. This is a significant amount, considering that modern sapiens from outside Africa retain about 2% of Neanderthal DNA. The most interesting thing is that these groups of sapiens never managed to settle in either Europe or Asia, and they completely died out.

About 120,000 years ago, another wave of Sapiens moved beyond their original continent, probably in search of game and new territories. The climate was favorable for them, creating a land bridge between Africa and the Sinai Peninsula, through which they reached the Middle East and the Arabian Peninsula. In this case, encounters must have been fewer, since the Neanderthals received only 0.5% of their DNA. Nor did this wave of migrants manage to stay in Europe, a continent where Neanderthals lived for hundreds of thousands of years, despite terrible ice ages.

In the final stages of this history, gene flow changed, and it was sapiens that began to receive important genetic contributions from their sister species. Between 60,000 and 50,000 years ago, sapiens occupied up to 10% of the Neanderthal genome, and this percentage increased with subsequent interbreeding.

And one last scary fact: the percentage of sapiens DNA in the last Neanderthals, who lived about 40,000 years ago, is zero. By then, they were the last human species to go extinct.

At this point, the work reveals a illuminating insight. The presence of sapiens DNA in the Neanderthal genome has led to their population size being overestimated to this day. The new calculation suggests they were 26% smaller, fewer than 2,500 individuals, spread out in small, isolated tribes across vast Europe. What’s more, they suffered from inbreeding and were burdened by the arrival of sapiens, whose clans were larger, better connected, and had the weapons to kill from a distance.

“Eventually, successive waves of sapiens immigration from Africa overwhelmed the Neanderthals until they could no longer remain a distinct species and were finally assimilated into the sapiens genetics,” says geneticist Joshua Akey, a co-author of the study.

Eiki adds: “We knew from previous studies that the Neanderthal presence on the X chromosome was much lower, which is related to the fact that hybrid boys survive less than girls. There are also indications that some Neanderthal genes were harmful and were removed from our genome. So it looks like there was some incompatibility in these crosses, but it must not have been very large, since it did not prevent sapiens from having Neanderthal ancestors and vice versa.” The Neanderthals are gone forever, but thanks to the fact that both species adopted and cared for their mixed-race children, their genetics are still alive and actively contribute to many physiological functions of sapiens, from fast blood clotting to a tendency to suffer from certain mental illnesses.

Geneticist Carles Lalueza-Fox was one of the first to talk about Neanderthal assimilation. A new study cites a Spanish researcher describing how unidirectional gene flow led to sapiens becoming more numerous and diverse when they interbred with Neanderthals, while they became fewer and weaker. Although the story can be more or less sad, depending on who is telling it. “Sometimes we think of the last Neanderthal as a lonely individual who can’t find a partner,” Lalueza-Fox explains. He adds: “I think of him more as someone who had a partner Homo sapiens“.

You can follow ITEM V Facebook, X And Instagramor sign up here to receive our weekly newsletter.