Do you like to get up early? You may have Neanderthal genes

Neanderthals were morning people, a new study suggests. And some modern-day humans who like to get up early might attribute that to genes they inherited from their Neanderthal ancestors.

The study, which compared DNA from living humans with genetic material from Neanderthal fossils, found that Neanderthals carried some of the same clock-related genetic variants as people who claim to be early risers.

Neanderthals and Denisovans, another group of hominids, disappeared from the fossil record about 40 thousand years ago. By then, modern humans had spread out of Africa, occasionally interbreeding with Neanderthals and Denisovans.

Today fragments of its DNA can be found in most living human beings. John Capra, a geneticist at the University of California, San Francisco, and his colleagues found that some of the most common Neanderthal and Denisovan genes across generations were related to sleep.

The researchers studied 246 genes that help control the biological clock, comparing the gene versions of extinct hominids with those of modern humans. They found more than a thousand mutations that were unique only to living humans or Neanderthals and Denisovans.

The scientists then polled the UK Biobank, a British database containing the genomes of half a million volunteers. Along with their DNA, volunteers provided answers to health-related questions, such as whether they were early risers or night owls.

To Capra's surprise, almost all of the biological clock variants inherited from Neanderthals and Denisovans made the volunteers more likely to be early risers.

“That was the most exciting moment of the study,” Capra said.

Geography could explain why ancient hominids were early risers. The first humans lived in Africa, relatively close to the Equator, where the length of days and nights is approximately equal throughout the year. But Neanderthals and Denisovans moved to higher latitudes, where the day became longer in summer and shorter in winter. Over hundreds of thousands of years, their circadian clocks may have adapted.

When modern humans spread out of Africa, they faced the same challenge of adapting to higher latitudes. After interbreeding with Neanderthals and Denisovans, some of their descendants inherited biological clock genes better suited to their new homes.

However, these conclusions arise from a database limited to Britons. Capra is beginning to probe other volunteer databases with a different genealogy. If the links hold, Capra hopes ancient biological clocks can inspire ideas about how we can adapt to the modern world, where circadian rhythms are disrupted by night work and shiny smartphones. These interruptions make it difficult to sleep and can increase the risk of cancer, obesity and other disorders.

By: CARL ZIMMER