No one knows exactly what happened to the Neanderthals. We know they died out, and our homo sapiens ancestors lived on. Since 2010, we’ve known that they interbred with our ancestors, as those of us who don’t originate in sub-Saharan Africa have genomes that contain 1 to 4 percent Neanderthal DNA. And as of today, we also know they might have something to do with our current propensity for depression.
In a study newly published in Science, Corinne Simonti and her team from Vanderbilt University found the places in our genomes where Neanderthal genetic variants are associated with known traits found in electronic medical records.
They found a goldmine of associations.
Some were physical conditions that are easily tied to the climates in which the Neanderthals lived. According to The Atlantic, those associations included skin disorders and blood clotting issues that might have originally been advantageous against UV radiation and diseases.
Unexpectedly, the team also found Neanderthal DNA to be a risk factor for psychiatric disorders–including depression. This doesn’t mean Neanderthals were responsible for depression, of course, but it does mean that it might have an influence.
Sun exposure influences depression risk, so the link between Neanderthal variants and mood disorders may again reflect their role in adapting modern humans to new climates. But that’s just a guess: “It seems Neanderthal DNA has an effect on systems that regulate our moods or behaviors,” says [Tony Capra, who led the study], “but for now, I don’t feel comfortable saying more than that.”
As Capra points out, these genetic links don’t tell us much–yet. What they give us is a new avenue of research.
“The Neanderthal genes are not disease agents,” says John Hawks from the University of Wisconsin-Madison, who was not involved in the study. But they’re “there in the brain, doing things, and having some detectable effects on behavioral outcomes. That’s amazing.” He and Capra both note that working out the role of these genes might help us to understand the underlying biology behind depression and other disorders.
The study was made possible through eMERGE (Electronic Medical Records and Genomics), a large-scale initiative to analyze the DNA of thousands of volunteers. Those analyses were compared against the volunteers’ medical records, allowing researchers to identify genes related to traits on a broad scale.
In 2011, the same data was used to explore genetic links between major depressive disorder and bipolar disorder, and in 2015 researchers used it to find a genetic relationship between Tourette’s syndrome and OCD. Our ancient genetic history may be fascinating, but it’s just one small part of what we can learn from this sort of shared data.