If you’re irritated by the morning people in your life, you might have Neanderthals to blame for their existence, at least a little bit. New research suggests that our hominin relatives possessed genetic variations that predisposed them to waking up early and that they passed on these genes to our Homo sapiens ancestors through interbreeding. The study also found evidence that some people today still carry that genetic legacy with them.
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Neanderthals (Homo neanderthalensis) are thought to be our closest extinct human relatives. Their lineage split away from the family tree branch that eventually gave rise to modern-day humans somewhere between 300,000 and 700,000 years ago (modern humans themselves emerged about 300,000 years ago). But they and other human species lived at the same time as our direct ancestors, with Neanderthals only dying out about 40,000 years ago. For most of their existence, Neanderthals lived in parts of what we now call Europe and Asia.
More recent research has shown that Neanderthals did more than just co-exist with Homo sapiens—they also boinked. This intermixing may have begun when modern humans left Africa some 70,000 years ago and spread across Europe and Asia, coming across Neanderthals in the area. Most populations of humans today are thought to have between 1% to 4% of their genome come from Neanderthals. And the authors of a new paper, published Thursday in the journal Genome Biology and Evolution, say that some of these persisting genes might help turn us into morning people.
Our propensity for being an early bird or night owl is largely affected by our circadian rhythm, or internal body clock. Though everyone’s body clock is roughly 24 hours, some research has suggested that having a shorter circadian period can make us better at falling asleep and waking up earlier. Other factors like an area’s latitude also affect our early bird/night owl type, and the team behind the new work cites research in animals indicating that having a shorter body clock can especially increase morningness in higher latitudes.
The group speculates that, since Neanderthals tended to live in higher latitude places, they would possess genetic variants tuned to make them early risers as a result. And when modern humans settled into these areas and mingled with Neanderthals, it’s these genes that would have had a better chance of sticking around and being passed down to today’s humans, since they continued to provide a possible evolutionary advantage.
To test their hypothesis, they first identified hundreds of potential genetic variations that could potentially affect circadian rhythm in both our direct human ancestors and Neanderthals. Then they used artificial intelligence to track down genetic variants that would likely result in clearly different body clocks for the two species. This finding also meant that it was possible for Neanderthals to transfer some of their circadian-related variants over to modern humans.
Next, the team scoured through data from the UK Biobank, a long-running research project that has collected genomes from hundreds of thousands of people, looking for variants thought to have originated from Neanderthals. Many of these variants were not only tied to people’s circadian rhythms but specifically associated with being an early bird.
“By combining ancient DNA, large-scale genetic studies in modern humans, and artificial intelligence, we discovered substantial genetic differences in the circadian systems of Neanderthals and modern humans,” said lead author John Capra, an epidemiologist at the University of California, San Francisco, in a statement from the journal’s publisher. “Then by analyzing the bits of Neanderthal DNA that remain in modern human genomes we discovered a striking trend: many of them have effects on the control of circadian genes in modern humans and these effects are predominantly in a consistent direction of increasing propensity to be a morning person.”
While Neanderthals may have helped make some people early risers, the study authors say there’s much left unknown about this influence. They now plan to run similar studies on other, more diverse populations of humans and test in the lab exactly how these Neanderthal genes could affect our morningness. They’d also like to look for other common traits shaped by our gone-but-not-forgotten human cousins.
