Scientists from Vanderbilt University, the University of Pennsylvania and the University of California ( USA ) have explained the genetic reasons why many people are larks. The reason for their existence is the crossing of people of modern anatomical type with Neanderthals and Denisovans, thanks to which adaptations were acquired to seasonal changes in light hours in Eurasia. The results of the study are published in the bioRxiv preprint archive .
It is known that the ancestors of the Neanderthals arrived in Eurasia before modern humans. They were forced to acquire many adaptations in order to survive in their new environment, including changing circadian rhythms to match the changing seasons and the associated length of the day. The lineages of archaic hominins and Homo sapiens diverged approximately 700,000 years ago and became geographically isolated as the ancestors of modern humans continued to live in Africa until the second wave of migration 60,000 years ago.
Scientists have followed the evolution of that part of the genome that determines the chronotype – individual characteristics in the daily rhythms of the body. After analyzing the genomes of archaic and modern humans, they found 28 circadian genes (regulating the daily activity of the body) that contain at least one mutation specific to Neanderthals or Denisovans and affecting splicing – the process of maturation of messenger RNA that carries information about the protein sequence. In addition, 16 circadian genes have been identified that are regulated differently in archaic and modern humans.
This indicates the existence of introgression, when genetic material is transferred from one species to another through repeated crossing of interspecific hybrids with one of the parent species. In this case, the descendants from the crossing of Neanderthals and Homo sapiens interbred with modern humans. The researchers found evidence for at least 26 circadian genes with traits of adaptive introgression, including PER2 and MYBBP1A.
The authors note that the strongest introgressive effects on the chronotype increase morning activity, which is consistent with adaptation to high latitudes in other species. Thus, the transfer of genetic material from Neanderthals and Denisovans actually caused people to become larks.