Neanderthals were morning people, a new study suggests. And some modern humans who like to get up early could attribute genes they inherited from their Neanderthal ancestors.
The new study compared DNA from living humans with genetic material recovered from Neanderthal fossils. It turns out that Neanderthals carried some of the same clock-related genetic variants as people who claim to be early risers.
Since the 1990s, studies of Neanderthal DNA have exposed the intertwined history of our species. About 700,000 years ago, our lineages split, most likely in Africa. While the ancestors of modern humans largely remained in Africa, the Neanderthal lineage migrated to Eurasia.
About 400,000 years ago, the population split in two. Hominids who spread westward became Neanderthals. Their eastern cousins evolved into a group known as Denisovans.
The two groups lived for hundreds of thousands of years, hunting and gathering plants, before disappearing from the fossil record about 40,000 years ago. By then, modern humans had expanded out of Africa, occasionally interbreeding with Neanderthals and Denisovans.
And today, fragments of its DNA can be found in most living humans.
Research in recent years by John Capra, a geneticist at the University of California, San Francisco, and other scientists suggested that some of those genes conveyed a survival advantage. Immune genes inherited from Neanderthals and Denisovans, for example, could have protected them from new pathogens they had not encountered in Africa.
Dr. Capra and his colleagues were intrigued to discover that some of the genes in Neanderthals and Denisovans that became more common over generations were related to sleep. For their new study, published in the journal Genome Biology and Evolution, they investigated how these genes could have influenced the daily rhythms of extinct hominids.
Within the cells of each animal species, hundreds of proteins react with each other throughout each 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 influence our appetite and metabolism.
To explore the circadian rhythms of Neanderthals and Denisovans, Dr. Capra and his colleagues looked at 246 genes that help control the biological clock. They compared the gene versions of extinct hominids with those of modern humans.
The researchers found more than 1,000 mutations that were unique only to living humans or to Neanderthals and Denisovans. Their analysis revealed that many of these mutations likely had important effects on the functioning of the biological clock. The researchers predicted, for example, that some biological 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 biological clock variants that some living people have inherited from Neanderthals and Denisovans. To see what effects those variants had on people, they tested the UK Biobanka British database containing the genomes of half a million volunteers.
Along with their DNA, volunteers provided answers to a long list of health-related questions, including whether they were early risers or night owls. To Dr. Capra’s surprise, almost all of the older variants of the biological clock made volunteers more likely to be early risers.
“That was really the most exciting moment of the study, when we saw that,” Dr. Capra said.
Geography could explain why ancient hominids were early risers. The first humans lived in Africa, fairly close to the equator, where the length of days and nights remains approximately the same 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 to the new environment.
When modern humans expanded out of Africa, they also faced the same challenge of adapting to higher latitudes. After interbreeding with Neanderthals and Denisovans, some of their descendants inherited biological clock genes that were better suited to their new homes.
All of these conclusions, however, arise from a database limited to the British. Dr. Capra is starting to look other databases of volunteers with other ancestries. If the links hold, Dr. Capra hopes ancient biological clocks can inspire some ideas about how we can adapt to the modern world, where circadian rhythms are disrupted by night shifts and shiny smartphones. These interruptions not only make it difficult to get a good night’s sleep; They can also lift the risk of cancerobesity and a host of 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 Dr. Capra’s variants would be to engineer several human cells in the lab so that their genes looked more like those. of Neanderthals and Denisovans. Scientists could then grow groups of cells and watch them go through their daily cycles.
“This step forward not only improves our knowledge of how Neanderthal DNA influences modern humans,” he said, “but also offers a path to expand our understanding of Neanderthal biology itself.”
