Evolution May Have Deleted Neanderthal DNA

Natural selection may be behind the dearth of Neanderthal DNA in modern humans.

By | November 9, 2016

WIKIMEDIA COMMONS, DRMIKEBAXTERThe modern human genome should, by all accounts, have more Neanderthal genes. Experts agree that early European and Asian humans almost certainly bred with Neanderthals, an ideal recipe for rich, complex genotypes 60,000 years later. And yet, non-African humans tend to have less than 4 percent Neanderthal DNA. Researchers may now have figured out why: in a November 8 PLOS Genetics study, scientists pinpoint natural selection, and the relatively large populations of humans versus Neanderthals, as reasons for these apparent reductions in Neanderthal DNA.

“The human population size has historically been much larger, and this is important since selection is more efficient at removing deleterious variants in large populations,” study coauthor Ivan Juric, population geneticist at 23andMe, said in a statement. “Therefore, a weakly deleterious variant that could persist in Neanderthals could not persist in humans.”

Juric and colleagues developed a method for quantifying the average strength of natural selection against Neanderthal genes. They found that selection against individual Neanderthal alleles is very weak, suggesting that our ancient ancestors accumulated many slightly deleterious alleles, which—within their small enclaves—were hardly noticeable when inherited. But once Neanderthals integrated into larger human populations, the researchers proposed, these alleles entered the crucible of natural selection and were weeded out of modern human genomes.

In the statement, Juric acknowledged that population size was but one factor. “Still,” he said, “I find it fascinating to think that if the Neanderthals had reached larger population sizes in Europe, or if modern human populations had grown slower, some of us today would probably carry a lot more Neanderthal ancestry in our genomes.”

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Avatar of: wctopp


Posts: 110

November 9, 2016

I wonder how easy it is to recognize Neanderthal DNA.  If I've got an A at some point in my gene for X and you've got a B, that doesn't mean that you've got a Neanderthal gene and I don't.  OTOH if you and I both have an A at that point it doesn't mean that I didn't get that A from a Neanderthal but you got it elsewhere.  Neanderthals were enough like us that many of their genes may not be recognizable as clearly different from ours.  What does appear to be lacking is any evidence that they contributed a strongly positive gene or two and I find that surprising.  Some of their genes had to be better at doing their thing than the African equivalent.  It had enormous amounts of time to emerge even in a sparse somewhat inbred population.

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