In the five years since scientists confirmed Neanderthal DNA is present in people of Eurasian ancestry, headlines have tended toward either the jocular or the melodramatic:
"Neanderthal chefs spiced up their diet" ... "Neanderthals drew first #hashtags" ... "Bone-chilling secrets of Neanderthal sex"
On Thursday, a straightforward, even prosaic headline was stripped across the top of an article in the journal Science:
"Neanderthal-Derived DNA May Influence Depression and More in Modern Humans"
If anything, that's an understatement.
The first-ever study directly comparing Neanderthal DNA to the human genome confirmed a wide range of health-related associations -- from the psychiatric to the podiatric -- that link modern humans to our broad-browed relatives.
"Our main finding is that Neanderthal DNA does influence clinical traits in modern humans," lead author John Capra, an evolutionary geneticist at Vanderbilt University, said in a statement.
Among the more intriguing points: Snippets of Neanderthal DNA contribute to the contemporary risk for myriad ills, including heart attack, nicotine addiction and mood disorders as well as incontinence, foot callouses and precancerous skin lesions.
Those skin conditions as well as depression are known to be influenced by sunlight exposure, which is why the researchers think Neanderthals' eventual migration from southern to northern hemispheres influenced their genetic susceptibility -- and ours.
"These results establish the impact of [Neanderthal] DNA on diseases that involve traits potentially influenced by environmental differences," they write.
The researchers concluded that Neanderthals likely lived long enough in their new homelands to adapt to a new environment. Some Neanderthal genes, appearing at a much higher frequency than the scientists expected, would have provided a benefit in early human populations as they moved between continents. But those same genes became disadvantageous hundreds of thousands years later.
One example is a genetic variant that increases blood coagulation. This trait might have aided wound healing in Neanderthals as they encountered new pathogens in more northern and western environments. Today, however, increased coagulation increases the risk of blood clots and strokes.
"The brain is incredibly complex," noted Corinne Simonti, a Vanderbilt doctoral student who was another lead author, "so it's reasonable to expect that introducing changes from a different evolutionary path might have negative consequences."
Neanderthals are thought to have migrated from Africa to Europe and Asia about 400,000 years ago. Interbreeding around 50,000 years ago resulted in the genomes of modern Eurasians containing between 1.5 percent and 4 percent Neanderthal DNA. Not long after, in epochal terms, Neanderthals went extinct during a particularly cold period on the European continent.
The study was a collaboration of 21 researchers from 10 different institutions, including Vanderbilt and the National Human Genome Research Institute. They began by accessing digitized health records managed by the Electronic Medical Records and Genomic Network, which links the data from nine hospitals around the country. One of them is Vanderbilt University Medical Center, which maintains a repository of patient DNA extracted from discarded blood tests.
The scientists searched for specific medical conditions and traits in 28,000 records, then analyzed the genomes of the patients to see if they carried Neanderthal DNA. Ultimately, this allowed the researchers to determine how these patients' ancient DNA might have influenced the risk for a host of medical conditions and traits.