Morning person? You may have Neanderthal genes to thank.

Neanderthals were morning people, A new study indicates. And some today’s early risers may credit the 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 reported being early risers.

Since the 1990s, studies of Neanderthal DNA have revealed the tangled history of our species. About 700,000 years ago, our lineages split, most likely in Africa. While the ancestors of modern humans remained largely in Africa, the Neanderthal lineage migrated to Eurasia.

About 400 thousand years ago, the population split into two parts. The hominins that spread westward became Neanderthals. Their cousins ​​to the east evolved into a group known as the Denisovans.

The two groups lived for hundreds of thousands of years, hunting and gathering plants, before they disappeared from the fossil record about 40,000 years ago. By then, modern humans had spread out of Africa, occasionally interbreeding with Neanderthals and Denisovans.

Today, parts of their DNA can be found in most living humans.

Research conducted by John Capra, a geneticist at the University of California, San Francisco, and other scientists over the past few years suggests that some of these genes convey a survival advantage. For example, immune genes inherited from Neanderthals and Denisovans may have protected them from new pathogens they did not encounter in Africa.

Dr. Capra and his colleagues were intrigued when they discovered that some genes from Neanderthals and Denisovans that had become more common over generations were linked to sleep. In their new study, published in the journal Genome Biology and Evolution, they investigated how these genes affected the circadian rhythms of extinct hominins.

Inside the cells of every animal species, hundreds of proteins interact with each other throughout each day, rising and falling on a 24-hour cycle. Not only does it control sleep and wake-up time, but it also affects our appetite and metabolism.

To explore circadian rhythms in Neanderthals and Denisovans, Dr. Capra and his colleagues looked at 246 genes that help control the body’s circadian clock. They compared versions of genes found in extinct hominins with those found in 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 may have important effects on how the body’s biological clock works. The researchers speculated, for example, that some circadian clock proteins that are abundant in our cells were very rare in Neanderthal and Denisovan cells.

Next, scientists looked at the small number of circadian clock variants that some living people had inherited from Neanderthals and Denisovans. To find out what effects these variables had on people, they conducted a study UK BiobankIt is a British database containing 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. To Dr. Capra’s surprise, almost all of the ancient body clock variables increased the odds that the volunteers were morning people.

“That was the most exciting moment in the study when we saw that,” Dr. Capra said.

Geography may explain why ancient hominins woke up so early. The first humans lived in Africa, fairly close to the equator, where the length of day and night remained 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 biological clocks may have adapted to the new environment.

As modern humans expanded out of Africa, they also faced the same challenge of adapting to higher latitudes. After they interbred with Neanderthals and Denisovans, some of their descendants inherited circadian genes better suited to their new homes.

However, all these conclusions stem from a database limited to British people. Dr. Capra began to look Other databases Volunteers from other origins. If the links hold, Dr. Capra hopes ancient body clocks will inspire some ideas about how to adapt to the modern world, where circadian rhythms are disrupted by night shifts and glowing smartphones. These disorders not only make it difficult to get a good night’s sleep; They can also raise it Risk of cancerObesity and a host of other disorders.

One way to test for Dr. Capra’s genetic variants is to engineer different human cells in the laboratory so that their genes are more like those of humans, said Michael Daneman, an evolutionary geneticist at the University of Tartu in Estonia who was not involved in the new study. Neanderthals and Denisovans. Scientists can then grow groups of cells and watch them go through their daily cycles.

“This step forward not only advances our knowledge of how Neanderthal DNA influenced present-day humans, but also provides a path to expanding our understanding of Neanderthal biology itself,” he said.