When Homo sapiens ventured from Africa into the colder lands of Eurasia, those ancient humans encountered other species of ancient humans and began … mixing their genes.

Those DNA-mixing events have passed genetic material down over tens of thousands of years, and now, researchers believe that they can pinpoint where a surviving mental health issue among modern humans came from.

But for once, we can’t blame the Neanderthals. The DNA in question comes directly from Denisovans. Researchers published a study in the journal PLOS Genetics in which they stated that the Denisovan-originated human gene variant SLC30A9 has passed into a majority of modern populations, and could be to blame for knocking off modern mental equilibrium.

SLC30A9 helps control the transportation of zinc across cell membranes.

The gene, coding for the ZnT9 protein, has some real benefits—especially in cold climates, as its role in cellular metabolism helped humans adapt to cold weather.

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But it has some cons as well. Namely, zinc imbalances may result in neurological abnormalities such as depression, hyperactivity disorder, autism spectrum disorder, and schizophrenia.

“We propose that adaption to cold may have driven this selection event,” the authors wrote, “while also impacting predisposition to neuropsychiatric disorders in modern humans.”

Continue here: Popular Mechanics