Early to bed and early to rise people can thank their ancient ancestors for the habit – or at least the Neanderthals with whom their ancestors procreated, scientists say.
DNA inherited from our thick-browed cousins may contribute to some people’s tendency to be larks, researchers have found, making them more comfortable getting up and going to bed earlier than others.
While most genes acquired by modern humans through ancient interbreeding have been wiped out by evolution, a small fraction remain, most likely because they helped early modern humans adapt to the new environment when they left Africa for Eurasia.
“By analyzing the bits of Neanderthal DNA that remain in modern human genomes, we discovered a striking trend,” said John Capra, an epidemiologist at the University of California, San Francisco. Many of them affected genes that control body clocks in modern humans, he said, in most cases “increasing propensity to be a morning person”.
Waves of Homo sapiens migrated from Africa to Eurasia about 70,000 years ago. Upon their arrival, they encountered the Neanderthals, who had already adapted to life in the colder climate, which had occupied the area hundreds of thousands of years earlier. Thanks to interbreeding between the groups, people alive today carry up to 4% Neanderthal DNA, including genes linked to skin pigmentation, hair, fat and immunity.
Capra and his colleagues analyzed DNA from modern humans and Neanderthals and found that different genetic variants were involved in the body clocks, or circadian rhythms, of the two groups. Since the ancestors of modern humans mated with Neanderthals, it was possible that some people alive today carried the Neanderthal variants, they reasoned.
To check, the researchers turned to UK Biobank, which contains genetic, health and lifestyle information on half a million people. Not only did many people carry the variants, the genes were consistently linked to early waking, the scientists write Genome Biology and Evolution.
But being a morning person doesn’t require Neanderthal genes. Hundreds of different genes influence when people sleep and wake, and there are also many environmental and cultural influences. In general, the Neanderthal genes have only a small impact.
Capra suspects that many modern humans carry Neanderthal genes because they helped their ancestors adapt to life at higher latitudes. “We don’t think being a morning person is actually what was beneficial. “Rather, we think it’s a sign of a faster running clock that can better adapt to seasonal variation in light levels,” Capra said. “At higher latitudes, it is beneficial to have a clock that is more flexible and can change better to match the changing seasonal light levels.”
Prof Mark Maslin, from University College London, who was not involved in the study, said: “Now we have genetic evidence that some of us really are morning people.
“When humans evolved in tropical Africa, day lengths averaged 12 hours. Now hunter gatherers only spend 30% of their waking time gathering food, so 12 hours is a lot of time. But the further north you go, the shorter and shorter the days become in the winter when food is particularly scarce, so it makes sense for Neanderthals and humans to start gathering food as soon as there is any light to work for.”
