What Did Neanderthals Leave to Modern Humans? Some Surprises

Claudia Dreifus, New York Times, January 20, 2017

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At Vanderbilt University, John Anthony Capra, an evolutionary genomics professor, has been combining high-powered computation and a medical records databank to learn what a Neanderthal heritage—even a fractional one—might mean for people today.

We spoke for two hours when Dr. Capra, 35, recently passed through New York City. An edited and condensed version of the conversation follows.

Let’s begin with an indiscreet question. How did contemporary people come to have Neanderthal DNA on their genomes?

We hypothesize that roughly 50,000 years ago, when the ancestors of modern humans migrated out of Africa and into Eurasia, they encountered Neanderthals. Matings must have occurred then. And later.

One reason we deduce this is because the descendants of those who remained in Africa—present day Africans—don’t have Neanderthal DNA.

What does that mean for people who have it?

At my lab, we’ve been doing genetic testing on the blood samples of 28,000 patients at Vanderbilt and eight other medical centers across the country. Computers help us pinpoint where on the human genome this Neanderthal DNA is, and we run that against information from the patients’ anonymized medical records. We’re looking for associations.

What we’ve been finding is that Neanderthal DNA has a subtle influence on risk for disease. It affects our immune system and how we respond to different immune challenges. It affects our skin. You’re slightly more prone to a condition where you can get scaly lesions after extreme sun exposure. There’s an increased risk for blood clots and tobacco addiction.

To our surprise, it appears that some Neanderthal DNA can increase the risk for depression; however, there are other Neanderthal bits that decrease the risk. Roughly 1 to 2 percent of one’s risk for depression is determined by Neanderthal DNA. It all depends on where on the genome it’s located.

Was there ever an upside to having Neanderthal DNA?

It probably helped our ancestors survive in prehistoric Europe. When humans migrated into Eurasia, they encountered unfamiliar hazards and pathogens. By mating with Neanderthals, they gave their offspring needed defenses and immunities.

That trait for blood clotting helped wounds close up quickly. In the modern world, however, this trait means greater risk for stroke and pregnancy complications. What helped us then doesn’t necessarily now.

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What has been the response to your Neanderthal research since you published it last year in the journal Science?

Some of it’s very touching. People are interested in learning about where they came from. Some of it is a little silly. “I have a lot of hair on my legs—is that from Neanderthals?”

But I received racist inquiries, too. I got calls from all over the world from people who thought that since Africans didn’t interbreed with Neanderthals, this somehow justified their ideas of white superiority.

It was illogical. Actually, Neanderthal DNA is mostly bad for us—though that didn’t bother them.

As you do your studies, do you ever wonder about what the lives of the Neanderthals were like?

It’s hard not to. Genetics has taught us a tremendous amount about that, and there’s a lot of evidence that they were much more human than apelike.

They’ve gotten a bad rap. We tend to think of them as dumb and brutish. There’s no reason to believe that. Maybe those of us of European heritage should be thinking, “Let’s improve their standing in the popular imagination. They’re our ancestors, too.’”

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