The world is split between morning people and night-owls (regularly blamed as lazy: “the early bird catches the worm”). But it might just be a question of genes, specifically Neanderthal genes. According to a study published in ”Genome Biology and Evolution”, Neanderthals, living in Eurasia, experienced more variations in seasonal daylight than humans living in Africa near the Equator. They were morning people.
Although evolutionary study is a constant work in progress, since the ‘90s scientists reckon that Neanderthals diverged some 700,000 years ago – probably in Africa – from the lineage that gave rise to modern humans, and they migrated North. That’s not the whole story: those migrants split too, about 400,000 years ago, Neanderthals going to the West and the group known today as Denisovans to the East. They both disappeared, according to the fossil records, about 40,000 years ago. Meanwhile, modern humans had expanded out of Africa too, sometimes interbreeding with both Neanderthals and Denisovans.
Genetic material retrieved from fossils enables scientists to compare our DNA with DNA from those extinct humanoids. According to John Capra, a geneticist at the University of San Francisco, having Neanderthal DNA may have offered some evolutionary advantages (for instance, protection from illnesses found in Eurasia and not in Africa).
But also, some of the genes from Neanderthal and Denisovans are related to sleep. Humanoids living in Euroasia may have adapted to seasonal variations of light in days and nights, making the most of daylight when they had it. Thus, those Euroasian Neanderthals may have had a more flexible circadian rhythm, our internal clock regulating the sleep-wake cycle.
The researchers compared 246 genes that help to control our body clock, finding over 1,000 mutations unique only to living humans and Neanderthal or Denisovans. They went on to compare data from the UK Biobank, a British database holding the genome of half a million volunteers who also answered a long list of questions related to their health. Bingo: those who had body-clock mutations coming from those ancient humanoids had more chance of being morning people.
There are, however, many factors influencing our circadian rhythm. Also, the study is only related to genetic material coming from the British database. Scientists are now examining other databases in the world. They also hope to find solutions for people who have sleep problems, exacerbated by stress and the glow of our smartphones at night.
