A recent study indicates that early hominids were morning people. And some modern humans who enjoy getting up early may attribute this to genes inherited from their Neanderthal ancestors.
The new research compared DNA from living humans to genetic material from Neanderthal fossils. It turns out that Neanderthals shared some clock-related genetic variants with people who claim to be early risers.
Studies of Neanderthal DNA have revealed our species’ intertwined history since the 1990s. Our lineages split about 700,000 years ago, most likely in Africa. While modern humans’ ancestors largely remained in Africa, the Neanderthal lineage migrated into Eurasia.
The population split about 400,000 years ago. The hominins that spread west became known as Neanderthals. Their cousins to the east evolved into the Denisovans.
The two groups hunted game and gathered plants for hundreds of thousands of years before disappearing from the fossil record around 40,000 years ago. By then, modern humans had spread beyond Africa, occasionally interbreeding with Neanderthals and Denisovans.
And today, DNA fragments from them can be found in the majority of living humans.
Neanderthal and Denisovan genes linked to sleep revealed survival advantage
Recent research by John Capra, a geneticist at the University of California, San Francisco, and colleagues suggested that some of those genes conferred a survival advantage. Immune genes passed down from Neanderthals and Denisovans, for example, could have protected them from pathogens they had never encountered before 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. They investigated how these genes might have influenced the daily rhythms of extinct hominins in their new study, which was published in the journal Genome Biology and Evolution.
Hundreds of proteins react with each other inside the cells of every animal species throughout the day, rising and falling in a 24-hour cycle. They not only control when we sleep and wake up, but they also have an impact on our appetite and metabolism.
Neanderthal and Denisovan genes influence body clock, favoring morning people
Dr. Capra and his colleagues looked at 246 genes that help control the body clock to investigate the circadian rhythms of Neanderthals and Denisovans.
They compared the gene versions in extinct hominins to those in modern humans.
The researchers discovered over 1,000 mutations that were only found in living humans, Neanderthals, and Denisovans. Their research revealed that many of these mutations had a significant impact on how the body clock worked. Some body-clock proteins that are abundant in our cells, for example, were predicted to be much scarcer in the cells of Neanderthals and Denisovans.
The researchers then examined the small number of body-clock variants that some living people inherited from Neanderthals and Denisovans. They investigated the UK Biobank, a British database containing the genomes of half a million volunteers, to see what effects those variants had on people.
Along with their DNA, the volunteers answered a slew of health-related questions, such as whether they were early risers or late-night owls. Dr. Capra was surprised to find that almost all of the ancient body clock variants increased the likelihood that the volunteers were morning people.
“That was really the most exciting moment of the study when we saw that,” Dr. Capra said.
Ancient hominins adapted body clocks to varied latitudes, influencing sleep
Geography may explain why ancient hominins awoke early. Early humans lived in Africa, near the Equator, where the length of days and nights remained roughly constant throughout the year. However, Neanderthals and Denisovans moved to higher latitudes, where the day lengthened in the summer and decreased in the winter. Their circadian clocks may have adapted to the new environment over hundreds of thousands of years.
When modern humans left Africa, they faced the same problem of acclimating to higher latitudes. They interbred with Neanderthals and Denisovans, and some of their descendants inherited body clock genes that were better suited to their new environments.
All of these conclusions, however, are based on a database that only includes British citizens. Dr. Capra is looking into other databases of volunteers with different ancestries. If the links hold up, Dr. Capra hopes that ancient body clocks can inspire some ideas about how we can adapt to the modern world, where night shifts and glowing smartphones disrupt circadian rhythms. These disruptions not only make it difficult to get a good night’s sleep; they can also increase the risk of cancer, obesity, and a variety of other diseases.
One way to test Dr. Capra’s variants, according to Michael Dannemann, an evolutionary geneticist at the University of Tartu in Estonia who was not involved in the new study, would be to engineer various human cells in the lab so that their genes were more like those of Neanderthals and Denisovans. Scientists could then grow clusters of the cells and observe their daily cycles.
“This step forward not only advances our knowledge of how Neanderthal DNA influences present-day humans,” he said, “but also offers a pathway to expanding our understanding of Neanderthal biology itself.”
