Wednesday, May 5

The oldest genome of a European reveals continuous sex with Neanderthals | Science


The skull of a woman who lived about 45,000 years ago in the Czech Republic, one of the remains analyzed.
The skull of a woman who lived about 45,000 years ago in the Czech Republic, one of the remains analyzed.

The bones of four people who lived in Europe 45,000 years ago have just shed some light on one of the darkest and most exciting chapters in the history of our species.

Among all of them stands out the faceless skull of a woman who lived in what is now the Czech Republic. The remains of the other three individuals, all male, were found in a cave in Bulgaria along with necklaces and punches typical of early modern human groups. Two teams of paleoanthropologists have managed to extract enough DNA from these fossils, the oldest known of our species, to reconstruct their entire genome.

The results show that one of the Bulgarian men had a Neanderthal relative less than 180 years ago. The other three individuals also had relatives of that species. All descended from hybrids of sex between Neanderthals and sapiens. The genome of the Czech Republic woman also contains 3% Neanderthal DNA. Before this study, only the genomes of two were known homo sapiens of the time, one that lived in Siberia about 45,000 years ago and another that lived in Romania about 40,000 years ago. They both carried Neanderthal DNA, in fact the second was a Neanderthal great-great-grandson.

All of this evidence, the study authors say, shows that crosses between Neanderthals and modern humans were much more frequent and recent than previously thought. In fact, their results support the theory that Neanderthals were never completely extinct, but were absorbed into the sapiens groups, which accepted them into their bosom.

This new data completes a history of inter-species sex that lasted tens of thousands of years.

“Interaction with Neanderthals must have been extremely frequent,” explains Svante Pääbo, the Swedish geneticist who has revolutionized human evolution research thanks to the analysis of ancient DNA and obtained the first complete genome of a Neanderthal. “The most surprising thing is that the three individuals from Bulgaria [y la de la República Checa] they had Neanderthal ancestors in their recent history ”, highlights Pääbo, who is the main author of the analysis of the Bulgarian fossils, published today in Nature. “This tells us that early modern humans interbred with Neanderthals frequently when they encountered them. It is possible that part of the explanation for the disappearance of Neanderthals is that they were simply absorbed by larger groups of our species ”, he highlights.

These new data complete a history of inter-species sex that spanned tens of thousands of years. The first evidence of a cross was found in the genome of a Neanderthal that lived 100,000 years ago in the Altai Mountains of Siberia and carried a significant fraction of DNA sapiens. Then, about 60,000 years ago, groups of sapiens that had left Africa in search of new territories encountered Neanderthals and crossed paths again. The last chapter happened already in Europe about 45,000 years ago and, judging by the evidence, it was widespread. As a result of this miscegenation, all current humans outside of Africa carry 2% Neanderthal DNA.

In a complementary article to the studies, geneticist Carles Lalueza-Fox puts forward a daring hypothesis. There is sufficient evidence that the sapiens had children with Neanderthals, cared for them and assumed them as their own, but there is little to the contrary, he explains.

“It is possible that modern humans tolerated hybrids and Neanderthals did not. Or it could be that Neanderthals rejected their hybrid children once they were born, ”writes Lalueza-Fox. The geneticist explains that the Neanderthal groups were very small and inbred, closed and isolated from each other. Meanwhile, the sapiens groups could be broader and more social, open to contact and collaboration with others. In any case, “the assimilation of Neanderthals is a very possible scenario, so that the only ones who survive in the end are those who end up in groups of sapiens. Afterwards, their genetic signal is diluted with the passage of time ”, he points out.

That is exactly what can be seen in the four humans analyzed: they had at least 3% Neanderthal DNA and genetic sequences much longer than humans today. Pääbo offers an explanation: “Previous studies have shown that after crosses, parts of the Neanderthal DNA were lost very quickly. One interpretation would be that in that DNA there were sequences that did not allow us to be a modern human, although we do not know what sequences they are.

The paleoanthropologist María Martinón-Torres believes that these works “tell us that only modern humans who had intimate contact with Neanderthals entered Europe, or in other words, that the Homo sapiens that finally managed to enter Europe was through a close relationship with Neanderthals ”. However, it warns of a limitation. “We cannot generalize too much from studies that are based on a few individuals. Can we imagine how controversial it would be if we made inferences about the origin of a current culture or population from the genetic study of only four people? ”, He highlights.

The genetic analysis of these remains uncovers migrations and extinctions of human groups unknown to date. Today’s humans in Asia and America still carry some of the DNA of the human group that lived in Bulgaria 45,000 years ago, which implies that this group migrated eastward and managed to survive. In contrast, the group of women in the Czech Republic, whose analysis is published in Nature Ecology & Evolution, disappeared forever without a trace in current populations. In the same cave in Bulgaria, the remains of a woman who lived 38,000 years ago and from whom modern Europeans do carry some DNA have been analyzed.

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