New research from the University of Washington finds DNA from ancient hominids can raise the risk of depression, tobacco addiction and heart attack — but only by a tiny margin.
Do you have bad skin or suffer from depression? Are you hooked on cigarettes or plagued by atherosclerosis?
New research from the University of Washington and Vanderbilt University suggests you might be able to ascribe a tiny bit of the blame to a distant ancestor’s dalliance with Neanderthals.
The study, published in the journal Science, examined the genes and medical records of 28,000 people to determine whether the small amount of Neanderthal DNA most humans carry in their cells still affects biology and health. More than 3,000 members of the Washington-based Group Health Cooperative were included in the analysis.
What the scientists found was a surprising number of links between genes passed down from the extinct hominids and a wide range of conditions, including depression, nicotine addiction, heart attacks, corns and calluses. In most cases, the effect was small, accounting for less than 2 percent of an individual’s total risk for any particular condition.
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“I would describe it as a pervasive but modest effect,” said UW geneticist Joshua Akey, a co-author of the study. “You can blame your Neanderthal ancestry a little — but not too much — for whatever range of afflictions you have.”
The discovery that ancient Homo sapiens occasionally mated with their stockier, beetle-browed cousins came just a few years ago, when scientists extracted Neanderthal DNA from fossil bones and compared it to the genome of modern humans.
Experts believe the two species encountered each other about 50,000 years ago, when modern humans were migrating out of their African birthplace into Eurasia — long the domain of Neanderthals. Some of those encounters led to hybrid offspring. As a result, people of Eurasian descent can trace 1 to 4 percent of their genetic material back to Neanderthal forebears.
Earlier studies found high concentrations of Neanderthal DNA in portions of the genome that influence skin, hair and parts of the immune system. The new research delved more deeply into the archaic DNA’s distribution and function.
The scientists tapped a vast repository called eMERGE, which contains medical records and genetic sequences from patients at nine sites across the country, including Group Health. The medical records yielded diagnoses for each patient, while the genetic sequences allowed the scientists to zero in on bits of DNA inherited from Neanderthals.
Then they compared the data sets to see if the presence of Neanderthal DNA raised or lowered the risk for certain diseases and conditions.
“Our main finding is that Neanderthal DNA does influence clinical traits in modern humans,” said senior author John Capra, of Vanderbilt. “Traits involved in the immune system, traits involved in our skin, but also psychiatric traits and neurological traits.”
While many of the associations appear negative from today’s perspective, interbreeding must have conferred some advantages on ancient humans, or natural selection would have largely purged the Neanderthal DNA after so long, said co-author Dr. Gail Jarvik, head of medical genetics at the UW.
For example, skin-related genes from Neanderthals may have helped modern humans adapt to the colder, less sunny climate of Eurasia. But today, those same genes appear to slightly raise the risk of certain types of skin lesions.
“I think this probably tells us more about what was important to our ancestors than what we should be worried about today,” Jarvik said.
Another set of Neanderthal genes, which foster rapid blood clotting, may have proved valuable in sealing wounds and preventing infection by unfamiliar germs that early humans would have encountered as they expanded their territory. Now, though, those genes seem to elevate the risk of stroke and other circulatory problems.
When it comes to depression, some Neanderthal genes raise the risk, while others lower it. And many key genes in the innate immune system, one of the body’s front-line defenses against infection, can be traced to Neanderthals.
“Maybe we have to take the bad with the good,” Akey said.
A better understanding of genetic variability and its sources can aid the quest for cures and treatments, he said.
“But for me, the thing that’s most fascinating about these studies is that we can take a look at DNA sequences of people today and make inferences about what happened 50,000 years ago.”