Neanderthal genes found in modern humans may have entered our DNA through an interval of interbreeding that began about 47,000 years ago and lasted nearly 7,000 years, new research shows.
Neanderthals were among the most extinct relatives of modern humans (Homo sapiens), with the ancestors of both lineages diverging about 500,000 years ago. More than a decade ago, scientists revealed that Neanderthals interbred with the ancestors of modern humans who migrated from Africa. Today it contains the genomes of modern human populations outside Africa about 1% to 2% of Neanderthal DNA.
Researchers are still unsure when and where Neanderthal DNA found its way into the modern human genome. For example, did Neanderthals and modern humans interbreed at one specific place and time outside Africa, or did they interbreed at many places and times?
To solve this mystery, researchers analyzed more than 300 modern human genomes over the past 45,000 years. These include samples from 59 individuals who lived between 2,200 and 45,000 years ago and 275 diverse contemporary modern humans. The scientists posted their findings on the internet BioRxiv preprint database. (As the study is currently under review for possible publication in a scientific journal, the study authors declined to comment.)
The scientists focused on how much Neanderthal DNA they could see in these modern human samples. By comparing how the level of Neanderthal ancestry varied in modern humans DNA at different locations and times, they were able to estimate when Neanderthals and modern humans interbred, and for how long.
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The best explanation for most of the Neanderthal DNA found in the modern human genome was a single major period of interbreeding about 47,000 years ago that lasted about 6,800 years, the researchers found.
If modern humans began to leave Africa at least 194,000 years ago, a likely place where they encountered Neanderthals was western Asia, where Africa connects to Eurasia, Chris Stringera paleoanthropologist at the Natural History Museum in London who was not involved in the new study told LiveScience. Modern humans with Neanderthal ancestry could then have spread around the world, he noted.
The scientists also examined how Neanderthal DNA persisted in the modern human genome over time. The longer a piece of Neanderthal DNA lasted, the more likely it was to provide modern humans with some evolutionary advantage. Conversely, the rapidly exterminated Neanderthal DNA likely presented some sort of evolutionary disadvantage. The researchers found that the Neanderthal genes that persisted are linked to skin color, metabolism and the immune systemwhich likely provided a direct benefit to modern humans as they faced new evolutionary pressures outside Africa.
Given the rate at which most Neanderthal DNA was eliminated from the modern human genome, the study estimated that when the newly identified period of interbreeding ended, more than 5% of the modern human genome was Neanderthal in origin. In other words, “about one in twenty parents in our ancestral population was a Neanderthal.” Fernando Villaneaa population geneticist at the University of Colorado Boulder who did not participate in this study told LiveScience.
Rajiv McCoy, a population geneticist at Johns Hopkins University in Baltimore who did not participate in this new work, told LiveScience that interbreeding between Neanderthals and modern humans may have occurred at other times, but they have not left lasting marks in modern times. human gene pool. For example, a modern human jaw from about 37,000 to 42,000 years ago found in Romania in 2002 possesses Neanderthal DNA not found in other modern human genomes, which could reflect an interbreeding event “that has not contributed to contemporary human diversity,” McCoy said.
Stringer noted that previous research suggested that the interbreeding that introduced Neanderthal DNA into the modern human genome occurred between 50,000 and 60,000 years ago. The new estimate of 47,000 years ago ‘has implications for… Homo sapiens spread outside Africa, because they all exist [living] Populations outside Africa – Chinese, Indians, Indonesians, indigenous Australians and so on – bear the marks of this event, which is therefore limited to when their ancestors began to disperse, to less than about 47,000 years ago,” Stringer said.
However, “there is archaeological evidence of human habitation in northern Australia approximately 65,000 years ago,” Stringer said. “So that evidence is wrong; the populations were Homo sapiens but they became extinct or were engulfed by a later dispersal; or the population was actually not Homo sapiensThe latter possibility “seems much less likely given the complex behavior implied by the evidence, but would of course be a huge bombshell.”
Curiously, the DNA exchange appears to have been one-way – meaning that modern human DNA does not appear to have made its way into the Neanderthals’ genomes. “There is currently little evidence that genes flow in the opposite direction, that is: Homo sapiens to Neanderthal man,” Stringer noted. ‘Maybe it happened, but we haven’t discovered it yet. Or perhaps it didn’t happen, with consequences for the behavior of the two populations.” Or perhaps such hybrids were less successful for some reason, he noted – perhaps they were less healthy or less fertile, for example.