Unless you’re African, your skin probably carries traces of your Neanderthal forebears.
According to new research, our ancient human ancestors acquired some skin genes that helped them survive outside Africa by mating with Neanderthals.
When humans wandered out of Africa and into Europe and Asia around a hundred thousand years ago, our closest hominid relatives, the Neanderthals, had already been there.
“So, of course, there’s always been the possibility that they would have met and that they would have interbred,” said genetics graduate student Benjamin Vernot at the University of Washington. “But there hasn’t been evidence for that. And we finally got evidence in 2010.”
That 2010 discovery found that non-Africans inherit about 1 to 3 percent of their DNA from Neanderthals.
The next question was, which 1 to 3 percent?
Vernot and his colleagues went looking through the genomes of 665 people for statistical patterns that would identify Neanderthal genes.
They published their findings in two scientific journals, Science
The scientists found several genes dealing with a protein called keratin, found in skin, hair and fingernails, that trace back to Neanderthals in more than 60 percent of those studied.
Vernot says those genes must have helped our ancestors adapt to the environment outside Africa. But he said they don’t know exactly how.
“We know that two of the genes are associated with pigmentation. So, it could be that we inherited lighter skin from Neanderthals,” he said. “But it’s really difficult to pin that down.”
“These two papers provide the first evidence that genes from Neanderthals affected modern humans in an important way: they were favored by natural selection,” said University of California at Berkeley geneticist Montgomery Slatkin, who was one of the scientists who sequenced the Neanderthal genome but was not involved in this research.
The scientists also were struck by how unevenly Neanderthal genes are spread throughout the human genome.
“There are places where lots of us share genes with Neanderthals, and there are places where nobody does,” said Harvard University geneticist Sriram Sankararaman.
The researchers found almost no Neanderthal versions of genes - called alleles - in parts of the genome dealing with fertility, for example.
And that makes sense, he added. “What we are seeing is the action of alleles that are causing incompatibilities being driven out of the population.”
Humans and Neanderthals were different species, and offspring of these kinds of mixed marriages “tend to be less fit or less fertile, or sometimes sterile,” said Sankararaman.
For example, horses and donkeys can mate, and they are more distantly related than humans and Neanderthals were. But they produce mules, which are sterile. So, genes that cause infertility would not survive.
Researchers also found Neanderthal genes in parts of the genome linked with a number of ailments, including diabetes, lupus, Crohn’s disease and smoking behavior.
“There, the interpretation is not very clear at all,” Sankararaman said. Researchers don’t know if those genes raise or lower the risk of disease.
“It doesn’t mean that the Neanderthal allele is causing a certain disease,” he added. “It’s just associated with that.”
So, if you can’t stop smoking, don’t blame the Neanderthals.