Depressed? Blame it on the Neanderthals

It turns out our Neanderthal ancestors passed on some genetic shortcomings that are responsible for a  range of modern day health problems from depression to stroke and even the difficulty of giving up smoking.

US scientists analysed the genomes of 28,000 adults and found the impact Neanderthal DNA had on 1,000 different clinical conditions.

The researchers analysed data from the Electronic Medical Records and Genomics Network, which contains genome information from patients of Vanderbilt University Medical Centre and other hospitals around the US.

They looked for Neanderthal DNA, which makes up 1% to 4% of the genome in people with Eurasian origin.

The scientists then analysed the patients’ anonymised electronic health records which contained information on clinical traits, such as dermatological, immunological or psychiatric diseases.

Some findings confirmed ideas that were already floating around. The study for instance showed Neanderthal DNA increases the risk of keratosis – thick, scaly pre-cancerous skin growths that can plague fair-skinned people.

Other associations were more surprising.

For one, Neanderthal DNA significantly increased the risk for nicotine addiction. It also increased the risk for mood disorders and depression.

“The brain is incredibly complex, so it’s reasonable to expect that introducing changes from a different evolutionary path might have negative consequences,” said the paper’s first author Corinne Simonti.

Many of these Neanderthal-specific genes, the authors say, would have helped our ancient ancestors discover new territory 40,000 years ago as they migrated out of Africa. Analysing medical records today is a new way to investigate these events in recent human evolution, they add.

The study for example linked Neanderthal DNA to high inflammation and blood clotting, so-called “hypercoagulation”. This would have helped Neanderthals seal wounds more quickly and fend off pathogens in new environments. But the trait has become redundant. In today’s (relatively) safe environment, blood that clots better is more likely to lead to strokes, pulmonary embolisms and pregnancy complications.

So is it all bad news? No – Neanderthal DNA was for instance linked to a reduction in digestive problems. (That’s not to say paleo diets would do the same today.)

So far the researchers have only analysed the medical records for physical symptoms.

The team, which published its findings in Science, are in the process of trawling through the records in more detail, analysing lab tests, medical images and doctors’ notes to uncover more about what the Neanderthals may have left us with.