by Neanderthals were morning people, a new study suggests. And some people today who want to get up early could credit the genes they inherited from their Neanderthal ancestors.
The new study compared DNA in living humans with genetic material obtained from Neanderthal fossils. It turns out that Neanderthals had some of the same clockwork genetic variants as humans who reported early success.
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Since the 1990s, studies of Neanderthal DNA have revealed the interconnected history of our species. About 700,000 years ago, our lines split from each other, probably in Africa. Although the ancestors of modern humans remained largely in Africa, the Neanderthal descendants moved into Eurasia.
Around 400,000 years ago, the population split in two. The hominins that spread back became Neanderthals. A group known as Denisovans evolved from their cousins to the east.
Both groups lived for hundreds of thousands of years, hunting game and gathering plants, before disappearing from the fossil record around 40,000 years ago. By then, modern humans had spread out of Africa, sometimes interbreeding with Neanderthals and Denisovans.
And today, fragments of his DNA can be found in most living people.
Research by John Capra, a geneticist at the University of California, San Francisco, and other scientists over the past few years suggested that some of these genes had a survival advantage. Immune genes inherited from Neanderthals and Denisovans, for example, may have protected them from new pathogens they had not encountered in Africa.
Capra and his colleagues were interested in finding out that some of the genes from Neanderthals and Denisovans that became more common over the generations were related to sleep. For their new study, published in the journal Genome Biology and Evolution, they investigated the impact these genes may have had on the daily rhythms of the extinct hominins.
Within the cells of every animal species, hundreds of proteins react with each other throughout the day, rising and falling in a 24-hour cycle. Not only do they control when we fall asleep and when we wake up, but they also affect our appetite and metabolism.
To explore the circadian rhythms of Neanderthals and Denisovans, Capra and his colleagues looked at 246 genes that help control the body’s clock. They compared the versions of the genes in the extinct hominins with those in modern humans.
The researchers found more than 1,000 mutations that were only unique to living humans or to Neanderthals and Denisovans. Their analysis showed that many of these mutations likely had important effects on how the body clock worked. The researchers predicted, for example, that some body-clock proteins that are abundant in our cells were much scarcer in the cells of Neanderthals and Denisovans.
Next, the scientists looked at the small number of body clock variants that some living humans inherited from Neanderthals and Denisovans. To see how those variants affected people, they explored the UK Biobank, a British database that has the genomes of half a million volunteers.
Along with their DNA, the volunteers provided answers to a long list of health-related questions, including whether they were early risers or night owls. Much to Capra’s surprise, almost every ancient version of body clocks increased the chance that the volunteers were morning people.
“That was the most exciting moment of the study, when we saw that,” Capra said.
Geography may explain why the early hominins became successful. Early humans lived in Africa, relatively close to the equator, where the length of the days and nights remains roughly the same throughout the year. But Neanderthals and Denisovans moved into higher latitudes, where the day was longer in summer and shorter in winter. Over hundreds of thousands of years, their circadian clocks may have adapted to the new environment.
When modern humans rose out of Africa, they also faced the same challenge of adapting to higher latitudes. After interbreeding with Neanderthals and Denisovans, some of their offspring inherited body clock genes that better suited their new homes.
All these conclusions, however, derive from a database limited to British people. Capra is starting to look at other volunteer databases with other elders. If the connections hold, Capra hopes ancient body clocks will prompt some ideas about how we can adapt to the modern world, where circadian rhythms are disrupted by night shifts and loud smartphones. Not only does this disruption make it difficult to get a good night’s sleep; they can also raise the risk of cancer, obesity and many other disorders.
Michael Dannemann, an evolutionary geneticist at the University of Tartu in Estonia who was not involved in the new study, said one way to test Capra’s variants would be to engineer different human cells in the lab so that their genes were more similar to those of Neanderthals and Denisovans. . The scientists could then grow clusters of the cells and watch them go through their daily cycles.
“This step not only advances our knowledge of how Neanderthal DNA influences people today,” he said, “but also provides a way to further our understanding of Neanderthal biology expand itself.”
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