Neanderthals were morning people, a new study suggests. And some modern-day humans who like to get up early might credit genes they inherited from their Neanderthal ancestors.
The new study compared DNA from living humans to genetic material recovered from Neanderthal fossils. It turns out that Neanderthals carried some of the same clock-related genetic variants as people who report being early risers.
Since the 1990s, studies of Neanderthal DNA have revealed the intertwined history of our species. About 700,000 years ago our lineages split, probably 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. The hominids that spread westward became the Neanderthals. Their cousins to the east evolved into a group known as the Denisovans.
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 this time, modern humans had spread out of Africa, sometimes interbreeding with Neanderthals and Denisovans.
And today, fragments of their 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 suggests that some of these genes convey a survival advantage. Immune genes inherited from Neanderthals and Denisovans, for example, could have protected them from new pathogens that they had not encountered in Africa.
Dr. Capra and his colleagues were intrigued to discover that some of the Neanderthal and Denisovan genes that became more common over generations were linked 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.
Inside the cells of every animal species, hundreds of proteins react with each other during each day, increasing and decreasing in a 24-hour cycle. They not only control when we fall asleep and wake up, but also influence our appetite and metabolism.
To explore the circadian rhythms of Neanderthals and Denisovans, Dr. Capra and his colleagues examined 246 genes that help control the biological clock. They compared the gene versions of extinct hominins to those of modern humans.
Researchers have discovered more than 1,000 mutations unique to living humans or Neanderthals and Denisovans. Their analysis revealed that many of these mutations likely had important effects on the functioning of the biological clock. For example, researchers predicted that certain biological clock proteins, abundant in our cells, were very rare in those of Neanderthals and Denisovans.
Next, the scientists looked at the small number of biological clock variants that some living people inherited from Neanderthals and Denisovans. To see what effects these variants had on people, they tested the UK Biobanka British database containing the genomes of half a million volunteers.
In addition to 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 body clock variants increased the chances that volunteers were morning people.
“That was really the most exciting moment of the study, when we saw this,” Dr. Capra said.
Geography could explain why ancient hominids got up early. Early humans lived in Africa, quite close to the equator, where the length of days and nights remains roughly the same throughout the year. But Neanderthals and Denisovans moved to higher latitudes, where days 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: adapting to higher latitudes. After interbreeding with Neanderthals and Denisovans, some of their descendants inherited biological clock genes better suited to their new home.
All these conclusions, however, come from a database limited to the British. Dr. Capra begins to examine other databases volunteers with other ancestors. If the connections hold, Dr. Capra hopes ancient biological clocks can inspire ideas about how we can adapt to the modern world, where circadian rhythms are disrupted by night shifts and glowing smartphones. These disruptions not only make it difficult to get a good night’s sleep; they can also increase 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 modify various human cells in the laboratory so that their genes more closely resemble those of Neanderthals and Denisovans. Scientists could then grow clumps of cells and watch them go through their daily cycles.
“This step forward not only advances our knowledge of how Neanderthal DNA influences modern-day humans,” he said, “but also provides a pathway to expand our understanding of biological Neanderthal itself. »