Neanderthal genes seen in modern humans may have entered our DNA through a period of interbreeding that began about 47,000 years ago and lasted about 7,000 years, according to new research.

Neanderthals were among modern humans’ closest extinct relatives; The ancestors of both lineages diverged about 500,000 years ago. More than a decade ago, scientists discovered that Neanderthals interbred with ancestors of modern humans who migrated from Africa. Today, the genomes of modern humans outside Africa contain approximately 1-2% Neanderthal DNA.

Researchers are still unsure when and where Neanderthal DNA entered the modern human genome. For example, did Neanderthals and modern humans mix at one particular place and time outside of Africa, or did they interbreed in many places and times?

To solve this mystery, researchers analyzed more than 300 genomes of modern humans from the last 45,000 years. These included samples from 59 individuals who lived between 2,200 and 45,000 years ago and 275 different modern humans. The scientists published their findings in the BioRxiv preprint database. (Since the study is currently under review for publication in a scientific journal, the study’s authors declined to comment.)

Scientists focused on how much Neanderthal DNA they could see in these modern human samples. Comparing how the level of Neanderthal ancestors changed DNA By studying modern humans in different places and at different times, they were able to estimate when and for how long Neanderthals and modern humans interbred.

The researchers found that the best explanation for most of the Neanderthal DNA in the modern human genome is a single major period of interbreeding that occurred about 47,000 years ago and lasted about 6,800 years.

Since modern humans began leaving Africa at least 194,000 years ago, the likely place they met Neanderthals was West Asia, where Africa meets Eurasia, said paleoanthropologist Chris Stringer of the Natural History Museum in London. The new study told Live Science. He stated that modern humans of Neanderthal origin may have later spread throughout the world.

The scientists also investigated how Neanderthal DNA was preserved over time in the modern human genome. The longer a piece of Neanderthal DNA has been around, the more likely it is that it may have provided evolutionary benefit to modern humans. By contrast, rapidly sorted out Neanderthal DNA probably carried some evolutionary disadvantages. The researchers found that surviving Neanderthal genes were associated with skin color, metabolism and the immune system, likely providing immediate benefits to modern humans facing new evolutionary pressures outside Africa.

Given the rate at which most Neanderthal DNA was removed from the modern human genome, the study estimates that more than 5% of the modern human genome was of Neanderthal origin by the time the newly identified period of interbreeding ended. In other words, “about one in 20 parents in our ancestral population were Neanderthals,” population geneticist Fernando Villanea of ​​the University of Colorado Boulder, who was not involved in the study, told Live Science.

Interbreeding between Neanderthals and modern humans may have occurred at other times, but it did not leave a permanent mark on the world, Rajiv McCoy, a population geneticist at Johns Hopkins University in Baltimore who was not involved in the new study, told Live Science. gene pool. For example, a modern human jaw from about 37,000 to 42,000 years ago found in Romania in 2002 contains Neanderthal DNA not found in other modern human genomes. This may reflect hybridization, which “does not contribute to modern human diversity,” according to McCoy. .

Previous studies have shown that the interbreeding that introduced Neanderthal DNA into the modern human genome occurred between 50,000 and 60,000 years ago, Stringer said. New estimate of 47,000 years ago “has distributional implications” homo sapiens Since they are all available except Africa [живі] Populations outside Africa (Chinese, Indians, Indonesians, indigenous Australians, etc.) bear signs of this event, marking the time when their ancestors began to disperse, less than about 47,000 years ago, Stringer said.

But Stringer said, “There is archaeological evidence of human presence in northern Australia around 65,000 years ago.” “So this evidence is either wrong; populations to which it belongs homo sapiens but they disappeared or were submerged as a result of later settlement; or that population wasn’t actually there homo sapiens The second possibility “seems much less likely given the complex behavior implied by the evidence, but it would certainly be a big bombshell.”

Interestingly, the DNA exchange appears to have been unidirectional; so modern human DNA does not appear to have entered the Neanderthal genome. “There is currently little evidence that gene flow is in the opposite direction; homo sapiens “To the Neanderthal,” Stringer pointed out. “Maybe it happened, but we haven’t discovered it yet. “Or maybe they didn’t, which has implications for the behavior of the two populations.” Or perhaps such hybrids were less successful for some reason, such as being less healthy or less fertile, he said.