WASHINGTON—Around 50,000 years ago, anatomically modern humans shacked up with some Neanderthals—and the genetic consequences are still doing a walk of shame through our generations.

The questionable interbreeding left traces of Neanderthal DNA that are linked to mood disorders, mostly depression, as well as tobacco-use disorders, skin conditions, and hypercoagulation (excessive blood clotting), according to a new study published Thursday in Science. The findings lend support to the theory that our past hominin hook-up has had a lasting influence on modern humans’ health. The data also offers hints at genetic adaptations of our ancient ancestors and, potentially, new insights into the diseases they help cause in modern humans, the authors suggest.

Having these traces of Neanderthal DNA doesn’t “doom us” to having these diseases, cautioned John Capra, bioinformaticist at Vanderbilt University and coauthor of the study. The genetic traces linked to disease in modern humans doesn’t mean that Neanderthals were stricken with those diseases either, he added. In fact, some of them could have been advantageous.

For instance, excessive blood clotting can result in strokes and heart attacks in modern humans. However, quick clotting is also a natural defense against bacteria entering a wound site, Capra explained.

He hypothesizes that some of the Neanderthal traces that linger in modern humans may have been advantageous at one point. This would make sense, since the Neanderthals were likely highly adapted to their own environments, he added. “Perhaps spending a night or two with a Neanderthal is a relatively small price to pay for getting thousands of years of adaptations,” Capra said.

Researchers have hypothesized for some time that Neanderthal DNA—the bits that have been maintained in modern humans’ genomes, that is—can influence health. After all, Eurasian genomes contain about 1.5 to 4 percent Neanderthal DNA. But proving that the tiny fragments of ancient DNA has influence has been tricky.

For the study, Capra and colleagues harvested genetic and disease incidence data from the electronic health records of more than 28,000 adults of European ancestry. Next, the researchers compared the genetic data with that of Neanderthal genomes, looking for genetic fingerprints of the ancient hominin’s DNA in modern genomes. Then they looked for links between the presence of Neanderthal DNA and disease incidence in the adults. Capra and colleagues found a number of links, some of which seemed to be associated with sunlight exposure, they speculated. The researchers found Neanderthal DNA variations associated with skin conditions, including actinic keratosis, precancerous skin lesions linked to over exposure to the sun. There were also Neanderthal links to depression, a mood disorder that can in some cases be linked to sun exposure in modern humans, the authors point out.

Less clear, however, was the link to tobacco-use disorders, which was found in the analysis. It’s unlikely that Neanderthals were taking smoke breaks 50,000 years ago outside their caves, Capra said. But the genetic hitch in modern humans in their modern environments may confer a complex neurological trait that now creates a predisposition to nicotine addiction. Studying the link further could offer new information on understanding and even treating addiction in humans, Capra explained.

Moving forward, Capra expects that more research using big genetic and disease datasets will reveal more ancient fragments of our genome and their influence on health. After all, he said, human’s family tree is a lot more bush-like than tree-like.

Science, 2015. DOI: 10.1126/science.aad2149 (About DOIs).