Since scientists discovered that Neanderthal DNA is present in people of Eurasian origin, hypotheses on the effects of these genes on modern human characteristics have abounded, from skin color to metabolism. Headlines like “Are Neanderthals to blame for your allergies?” saw print and fueled this line of curiosity.

Now, a new study saw that a certain bit of this DNA significantly upped risks for nicotine addiction and depression, and generally influenced clinical traits in modern humans.

“We discovered associations between Neanderthal DNA and a wide range of traits, including immunological, dermatological, neurological, psychiatric and reproductive diseases,” reported senior study author and evolutionary geneticist John Capra of Vanderbilt University in a press release.

The scientists used a database of 28,000 patients whose DNA samples have been matched with anonymized versions of their digitized health data, which came from records from Vanderbilt and eight other hospitals through the Electronic Medical Records and Genomic Network of the National Human Genome Research Institute.

The data informed researchers if each person had ever been treated for certain medical conditions. The researchers then analyzed each person’s genomes to pinpoint the unique Neanderthal DNA set individually carried.

Some of the team’s findings confirmed earlier hypotheses, such as the Neanderthal DNA affecting keratinocytes, cells that help protect the skin from UV radiation and other environmental assaults. It particularly increases the risk of developing keratosis, skin lesions caused by abnormal forms of these cells.

The team was surprised to discover that parts of the DNA were linked to psychiatric and neurological effects, which translated to a higher risk of getting addicted to smoking or becoming depressed.

First author Corinne Simonti explained that since the brain is a greatly complex organ, introducing changes from an altogether different evolutionary path could lead to negative impacts such as these predispositions.

Neanderthals are believed to have migrated from Africa to Europe as well as Asia some 400,000 years ago, with interbreeding about 50,000 years ago resulting in the genomes of modern Eurasians having up to 4 percent Neanderthal DNA. Neanderthals became extinct during a cold spell in the European continent.

Thus, today’s population is believed to retain Neanderthal DNA that gave early humans adaptive strategies at the time that they moved into new non-African settings, which had different pathogens and sun exposure levels.

Sadly, many of those traits may no longer be an advantage today.

Here’s an example: a gene variant raises blood coagulation rate, which could have assisted our ancestors in coping with pathogens present in new environments. This variant helped seal wounds faster and prevent pathogenic invasion.

Now, the gene variant has turned detrimental as excess coagulation ups the risk for conditions such as stroke, pulmonary embolism and complications in pregnancy.

The study is limited to linking the DNA variants with physical characteristics noted in hospital billing codes, but Capra’s team is currently using other data in medical records such as lab tests and medical images to expand their research.

The findings were published Feb. 12 in the journal Science.

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