The Legacy of Neanderthals

Once our closest relatives, Neanderthals were recently discovered to have interbred with modern humans, accounting for anywhere between 1.5 and 2.1 percent of DNA in people outside Africa. This left many scientists wondering whether this genetic legacy is somehow continuing to impact our species.

According to a new study reported in Scientific American, genetic variants of Neanderthal origin were “significantly linked” to a greater risk of 12 conditions, including heart attack, artery thickening, and even nicotine addiction.

Some of the scientists’ discoveries confirm previous ideas. For example, earlier research suggested that Neanderthal DNA influenced skin cells known as keratinocytes that help protect the skin from environmental damage such as ultraviolet radiation and germs. The new findings suggest that Neanderthal genetic variants increase the risk of developing sun-triggered skin lesions known as keratoses, which are caused by abnormal keratinocytes.

“When we started this study, we expected that if we found anything at all, we would find an influence of Neanderthal DNA on bodily systems that are involved in interactions with the environment,” Capra said. “We hypothesized this because Neanderthals had been living in Central Asia and Europe for hundreds of thousands of years before our recent ancestors ever reached these areas—and thus had likely adapted to the distinct environmental aspects of these regions, compared to Africa, in terms of climate, plants and animals, and pathogens.”

Capra and his colleagues also found that a number of Neanderthal genetic variants influenced the risk for depression, with some variants increasing the risk and others reducing it.

“The brain is incredibly complex, so it’s reasonable to expect that introducing changes from a different evolutionary path might have negative consequences,” study lead author Corinne Simonti, a graduate student of human genetics at Vanderbilt University, said in a statement.”

It is fascinating to think that Neanderthals are still with us, in some sense, tens of thousands of years later, influencing a range of biological factors. And while the legacy of our partial Neanderthal heritage — again, only for those outside of Africa — seems negative, it may have actually been key to our initial evolutionary success.

The researchers suggest that some Neanderthal genetic variants might have provided benefits in modern human populations as they first moved out of Africa thousands of years ago. However, those variants may have later become detrimental in modern, Western environments, the scientists said. One example is Neanderthal DNA that increases blood clotting; while this can help seal wounds and prevent germs from entering the body, it can also increase the risk for stroke, miscarriage and other problems, Capra said.

The researchers suggest that Neanderthal DNA may not have contributed to differences in skin colors between modern humans, unlike what previous research has suggested. Instead, differences in modern human skin color probably developed very recently, Capra said. “Neanderthals may also have had a range of skin colors,” Capra added.

Future research can compare Neanderthal DNA with data gleaned from other sources of medical information, such as lab tests, doctors’ notes and medical images, the researchers said. “There is still much to learn about the effects of interbreeding on different populations in recent human history,” Capra said.

Pretty fascinating stuff.

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