Getting up before the first morning light and with the chickens on the roost, some people don’t want it any other way. These early birds may owe their habit to Neanderthals.

All modern humans trace their origins to Africa about 300,000 years ago. The environment and climate influenced the evolution of our ancestors. About 70,000 years ago they moved to Asia and Europe. There they encountered a completely different climate. Not only was it much colder, the amount of daylight in summer and winter also fluctuated much more than they were used to.

Chewing and darkness
Other hominids, such as Neanderthals and Denisovans, had lived in Eurasia for more than 400,000 years and were therefore used to the cold and the difference between the seasons. They split from modern humans about 700,000 years ago and developed in a completely different climate. As a result, they had a specific gene package that differed considerably from that of modern humans. However, when the latter moved towards Asia, they soon crossed with these other branches. These early humans thus received a number of genes from Neanderthals. And while most specimens of these hominids were not that useful and thus disappeared, a few were preserved. Consider ancient genetic variants linked to differences in hemoglobin levels in Tibetans who live at high altitudes, immune resistance to new diseases, the amount of skin pigment and fat composition.

Plus genetic variants that influence the biological clock and thus help adapt to the variation in daylight. At least, that’s what the researchers suspected; it had not been studied in humans until now. So they looked for genetic evidence for differences in this circadian clock of Neanderthals and modern humans.

Hundreds of genetic variants
And with success. They identified 246 genes and hundreds of genetic variants in both Neanderthals and modern humans, which could potentially influence genes involved in the biological clock. Using artificial intelligence, they identified 28 genes that contained variants with the potential to alter splicing in archaic hominins and 16 circadian genes that were aberrantly regulated in early hominins and modern humans. Since Neanderthals and humans interbred, it seems logical that some humans inherited circadian variants from Neanderthals.

To test this, the researchers looked to see whether the genetic variants that passed from Neanderthals to modern humans were linked to the body’s preference for waking and sleeping. To do this, they used the data of hundreds of thousands of people from the British Biobank, the well-known database with long-term health data of at least half a million Britons. And it was perfect. There appeared to be many genetic variants with an effect on sleep preference. In fact, the researchers discovered that these variants increase the chance of being an ‘early bird’, or the extent to which we are morning people. So it seems that we inherited our need to get up early straight from the Neanderthals.

Useful for getting up early
That has been particularly useful in the past. The need to get up early and go to bed early is associated with a shorter biological clock. This is useful at higher latitudes, because it has been shown that it is easier to adjust the sleep/wake rhythm to the amount of daylight. In fruit flies, for example, it has already been proven that a shorter circadian period makes it much easier for the animals to adapt to the long summer days.

This seems to be the case with humans too. The preference for being a morning person probably had an evolutionary advantage for our ancestors who came to live in Europe. So it was a useful genetic trait to inherit from the Neanderthals.

Early birds
Lead researcher John Capra explains how they made this special discovery. “By combining ancient DNA, large-scale genetic studies in modern humans and artificial intelligence, we have discovered substantial genetic differences in the circadian systems of Neanderthals and modern humans,” he explains. “We then analyzed bits of Neanderthal DNA that have survived in the human genome and discovered an unusual trend: many of those genes influence the control of circadian genes in modern humans, and they are overwhelmingly in the direction of our tendency to have a to be a morning person. This adjustment is consistent with the effect on the biological clock of life at higher latitudes and likely allows us to align our internal clock with the changing amount of daylight seasonally,” the researcher said.

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