Neanderthal DNA May Help Explain Why Some People Are Early Risers

If you’re a morning person, you may be able to thank your Neanderthal ancestors for your easy ability to wake up. Some people today might be early risers because of DNA they inherited from Neanderthals tens of thousands of years ago, suggests new research published Thursday in the journal Genome Biology and Evolution.

When early humans migrated from Africa to Eurasia roughly 70,000 years ago, some of them mated with Neanderthals, who had already adapted to the colder, darker climates of the north. The ripple effects of that interbreeding still exist today: Modern humans of non-African ancestry have between 1 and 4 percent Neanderthal DNA.

Some of that DNA relates to sleep—more specifically, the internal body clock known as the circadian rhythm. For the new study, researchers compared DNA from today’s humans and DNA from Neanderthal fossils. In both groups, they found some of the same genetic variants involved with the circadian rhythm. And they found that modern humans who carry these variants also reported being early risers.

For Neanderthals, being “morning people,” might not have been the real benefit of carrying these genes. Instead, scientists suggest, Neanderthals’ DNA gave them faster, more flexible internal body clocks, which allowed them to adjust more easily to annual changes in daylight.

“In general, it seems that having a faster running clock leads people [and other organisms] to be earlier risers and have an easier time adapting to seasonal variation,” says study co-author John Capra, an evolutionary and computational geneticist at the University of California San Francisco, to Popular Science’s Laura Baisas.

This correlation makes sense in the context of human history, says Mark Maslin, an earth systems scientist at University College London who was not involved in the research, to the Guardian’s Ian Sample.

When early humans moved north out of Africa, they would have experienced variable daylight hours—shorter days in the winter and longer days in the summer—for the first time. The Neanderthals’ circadian rhythm genes likely helped early humans’ offspring adapt to this new environment.

“When humans evolved in tropical Africa, the day lengths were on average 12 hours long,” Maslin tells the Guardian. “Hunter gatherers spend only 30 percent of their awake time collecting food, so 12 hours is loads of time. But the farther north you go, the shorter and shorter the days get in winter when food is particularly scarce, so it makes sense for Neanderthals and humans to start collecting food as soon as there is any light to work by.”

Notably, the findings do not prove that Neanderthal genes are responsible for the sleep habits of all early risers. Lots of different factors beyond genetics can contribute to when people wake up, including social and environmental influences.

The study also only included DNA from people living in the United Kingdom—it came from a database called the U.K. Biobank—so the findings may not necessarily apply to all modern humans. Next, the research team hopes to study other genetic databases to see if the same link holds true for people of other ancestries.

If the findings do apply more broadly, they may one day be useful for improving sleep in the modern world, reports the New York Times’ Carl Zimmer.

Sleep and wakefulness patterns are far from the only traits that can be traced back to Neanderthals. Their genetics may also play a role in humans’ hair color, skin tone, mental health, weight and even some behaviors, like smoking. Neanderthal DNA has also been linked with a variety of diseases in humans, including heart disease.

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.