DNA Testing Suggests Limited Human-Neanderthal Interbreeding
Neanderthal genes seen in modern humans may have entered our DNA through an interval of interbreeding aroud 47,000 years ago
Neanderthals were among the closest 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 out of Africa.
Today, the genomes of modern human populations outside Africa contain about 1% to 2% of Neanderthal DNA.
Researchers are still unsure about when and where Neanderthal DNA made its way into the modern human genome. For instance, did Neanderthals and modern humans intermingle 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 spanning the past 45,000 years. These included samples from 59 individuals who lived between 2,200 and 45,000 years ago and 275 diverse present-day modern humans.
The scientists posted their findings on the BioRxiv preprint database. (As the study is currently under review for potential publication in a scientific journal, the study’s 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 human DNA across different locations and times, they could estimate when Neanderthals and modern humans interbred, and for how long.
As modern humans started leaving Africa at least 194,000 years ago, a likely place for them to encounter Neanderthals was western Asia, where Africa connects with Eurasia, Chris Stringer, a paleoanthropologist at the Natural History Museum in London who was not involved in the new study, told Live Science.
Modern humans bearing Neanderthal ancestry could have then dispersed across the globe, he noted.
The scientists also investigated how Neanderthal DNA persisted in the modern human genome over time. The longer a chunk of Neanderthal DNA lasted, the more likely it bestowed some kind of evolutionary benefit to modern humans.
Conversely, Neanderthal DNA that got weeded out quickly likely conferred some type of evolutionary disadvantage. The researchers found the Neanderthal genes that lasted are linked to skin color, metabolism and the immune system, likely providing some kind of immediate benefit to modern humans as they encountered 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 20 parents in our ancestral population was a Neanderthal,” Fernando Villanea, a population geneticist at the University of Colorado Boulder who did not take part in this study, told Live Science.
Rajiv McCoy, a population geneticist at Johns Hopkins University in Baltimore who did not participate in this new work, told Live Science that interbreeding between Neanderthals and modern humans may have also taken place at other times, but that these did not leave any lasting traces in the modern human gene pool.
For instance, a modern human jaw from about 37,000 to 42,000 years ago found in Romania in 2002 possesses Neanderthal DNA not seen in other modern human genomes, which may reflect an interbreeding event “that did not contribute to contemporary human diversity,” according to McCoy.
Stringer noted that prior research suggested that the interbreeding that introduced Neanderthal DNA into the modern human genome took place between 50,000 and 60,000 years ago.
The new estimate of 47,000 years ago “has implications for Homo sapiens dispersals outside of Africa, because all extant [living] populations outside of Africa — Chinese, Native Americans, Indonesians, Native Australians and so on — carry the signs of this event, which therefore constrains when their ancestors began to disperse, to less than roughly 47,000 years ago,” Stringer said.
However, “there is archaeological evidence of human occupation in northern Australia about 65,000 years ago,” Stringer said. “So either that evidence is wrong; the populations were Homo sapiens but they went extinct or were swamped by a later dispersal; or the population was not, in fact, Homo sapiens.”
The latter possibility “seems much less likely given the complex behavior implied by the evidence, but would be a huge bombshell, of course.”
Curiously, the exchange of DNA appears to have been one way — meaning modern human DNA seems to have not entered Neanderthal genomes. “There is little evidence of gene flow in the reverse direction at this time — that is, Homo sapiens to Neanderthal,” Stringer noted.
“Maybe it did happen but we haven’t yet detected it. Or perhaps it did not happen, with implications for the behavior of the two populations.”
Or perhaps such hybrids were less successful for some reason, he noted — for instance, perhaps they were less healthy, or less fertile.
See more here livescience.com
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Howdy
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“Neanderthal genes seen in modern humans may have entered our DNA through an interval of interbreeding aroud 47,000 years ago”
Such shortsightedness. Why could it not be intentional?
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Wisenox
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I’m neander, and happy about it. I suspect that the mixing with Neanderthals gave us a spark of intelligence, and perhaps neither species was as intelligent as the offspring.
Akin to the Liger, the mixing likely had different results if the Neander was the mother or father. Differences in cranial structure may have contributed to convolutions and intelligence. The offspring may have been very large if the mother was one of the species, but smaller if the mother was the other species; maybe even sterile.
I credit modern human’s ability to visualize abstract concepts to the neander side.
It would be nice to see if historical innovations predominantly arise in neander-mix populations, or elsewhere.
I’m an introvert and part neander, and I like them both.
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Evolution Denier
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What a sophisticated Photoshopped image of a Neanderthal! But that’s all evolution theorists have is fabricated pictures, altered bones and skulls, and fictional animations. Any artist for hire can make pictures that are lies and not real! Any sculptor for hire can cleverly take chimp facial bones and fuse them to a human skull. Pictures and fabricated bone fragments do not make evolution true.
Evolution theorists have a monopoly on teaching their “evolution religion” in the public schools and on MSM, and at all the government owned natural “history” museums across the land. So the public accepts evolution as probably true to some extent.
But thinking people see through the Photoshopped pictures of Neanderthals, and the hoax skulls, the animations, and phony illustrations in National Geographic magazine. Thinking people know that evolution is false. Thinking people go to the zoo, and the zookeeper never finds an apeman baby born in the chimpanzee cage in the morning! The only thing that is ever born in the chimp cage is another chimp!
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sunsettommy
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Your comment was all opinion, try to add some science into it next time.
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S.C.
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Dear Kettle, you are black. signed Pot.
It seems to me that a good example of ‘natural selection’ exponentially sped up exists as part of our every day lives. Canines and people teamed up at least 10,000 years ago. Humans, being the dominant partner, have taken on the role of selector, but, natural or not, traits deemed favorable have been enhanced through breeding, and bad traits likewise weeded out. This, of course is where the various breeds came from.
For the most part, modern dogs’ ancestry lies in wolves. So, if chihuahuas and huskies and setters all came from wolves, does this support the theory of evolution? I say no. Regardless of the breed, show one to any two year old and she will point and say “doggie.”
No new species have arisen, only various genes have been turned on or off. This is not the same thing as theoretical species jumping because the genes were already there, just recessive.
As for random mutation, it almost always means certain death in the natural world, especially mutations severe enough to alter the number of chromosomes.
There are countless logical errors in evolution, and I won’t go into any of them now, but as Evolution Denier said, “The only thing that is ever born in a chimp cage is another chimp.”
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sunsettommy
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That is an interesting viewpoint however there are NEW genetic combinations created which is why we have so many variations of the dog family when it used to be just wolves in the beginning that is a clear statement of evolution in progress which is why modern dogs are not called wolf at all.
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Herb Rose
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There is obviously a feedback system from the environment directing development and converted into inherited traits. It is not just an exploitation of a random mutation but some direction, based on conditions. DNA may be the blueprint but it is the proteins that determine what parts of the design are used and what proteins are available depends on diet. .
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