Depression affects 350 million people worldwide; could Neanderthals be to blame? A new study says yes, and it attributes 12 different conditions that plague humanity to Neanderthal-derived DNA.

There’s been a lot of disagreement in the scientific community about the influence of Neanderthal-derived DNA on modern humans. A 2012 study argued that Neanderthals only have similar DNA to modern humans because they share a common ancestor, but this perspective is not widely held.

Most scientists believe that Neanderthals bred with anatomically modern humans before going extinct. When those humans first emigrated from Africa and encountered Neanderthals in Asia and Europe, they interbred so frequently, scientists say, that most people today have a tiny bit of Neanderthal DNA preserved in their genes.

In past research, parts of the human genome have been found to carry genetic variants derived from Neanderthals, and it is estimated non-African humans inherited 1.5 to 4 percent of their DNA from Neanderthals. But because Neanderthal DNA is so difficult (and expensive) to identify in individuals, scientists have not been able to fully understand and agree upon the role of Neanderthal-derived DNA on modern human traits — until now.

By comparing a map of Neanderthal haplotypes (groups of genes inherited together), with the electronic health records of 28,000 adults of European descent, study author Corinne Simoniti and colleagues were able to correlate individual Neanderthal alleles (gene variants) with human phenotypes (observable traits).

The researchers found that Neanderthal-derived DNA was associated with 12 medical conditions affecting our skin, immune system, metabolism, and mental health, including depression, myocardial infarction, and blood disorders.

The study’s authors state that these Neanderthal alleles may have helped our ancestors move out of Africa, but in the modern era, have become harmful in Western environments.

Source: Simonti CN et al. The phenotypic legacy of admixture between modern humans and Neandertals. Science. 2016