Harmful Neanderthal genes
Neanderthals gave people a tendency to narcolepsy and schizophrenia
Ekaterina Rusakova, N+1
Geneticists have identified some of the gene variants that Neanderthals passed on to ancient humans. Among the characteristics associated with these genes was the "owl" chronotype; the ability of the skin to tan or burn in the sun, as well as the regulation of the level of "bad" cholesterol, eating disorders and other diseases. The research results are presented in two articles published in The American Journal of Human Genetics and Science (Michael Dannemann, Janet Kelso, The Contribution of Neanderthals to Phenotypic Variation in Modern Humans).
Ancient people, Homo sapience, migrated from Africa to Eurasia about 70-75 thousand years ago. Along the way, they interbred with other subspecies of humans, including Neanderthals, who apparently lived in the Middle East.
Neanderthal Habitat (Ryulong / Wikimedia Commons)
As a result, about two percent of Neanderthal genes appeared in the genome of humans, with the exception of the indigenous inhabitants of Tropical Africa. To date, it is known that some of them have helped people adapt to unfamiliar conditions: to acquire resistance to diseases unknown in Africa. Some Neanderthal genes encode proteins that affect immunity and skin pigmentation. But what role most of the genes inherited from ancient people play (and whether they play at all) is still unclear.
Geneticists from the Institute of Evolutionary Anthropology of the Max Planck Society decided to clarify this question. They analyzed the genomes of 112 thousand people from the UK Biobank and identified 13 archaic haplotypes with Neanderthal genes found in modern humans.
As it turned out, among the Neanderthals there were gene variants associated with influencing human behavior. Some of them are associated with the preferred chronotype of "owls", the tendency to sleep during the day and narcolepsy; others affect the feeling of loneliness. The authors of the study confirmed some of the results found in other papers (1, 2, 3). So, they found among Neanderthal genes mutations associated with mood disorders and the likelihood that a person will smoke; gene variants associated with the regulation of skin tone and its ability to tan (or burn in the sun), and determining hair color. Scientists note that, apparently, among Neanderthals, as well as among modern humans, there were individuals with different skin tones and hair color. At the same time, Neanderthal variants responsible for these traits were found no more often than gene variants of modern humans. The only exception was the red hair color. Researchers did not find a mutation associated with it in archaic haplotypes.
According to scientists, many of the Neanderthal features they discovered — hair and skin tones, chronotype, mood features — are due to exposure to sunlight. By the time modern humans arrived in Eurasia, Neanderthals had lived here for about a hundred thousand years, and apparently had already adapted to a lower level of ultraviolet radiation and a wider range of daylight. Researchers believe that the amount of sunlight influenced the phenotype of Neanderthals, and that Neanderthal gene variants contribute to the change in the phenotype of modern humans today.
The second work was carried out by an international team of researchers, including scientists from Germany, the USA and Russia. In it, geneticists determined the sequence of the nuclear DNA of a Neanderthal woman who lived about 50 thousand years ago. Her remains were found in the Vindija cave in northern Croatia. The cave is known for the fact that very well-preserved remains of Neanderthals were found in it. The researchers were able to isolate pure DNA (the level of contamination did not exceed one percent) and obtain a high-quality genome.
By analyzing the resulting DNA sequence, scientists were able to estimate when the populations of subspecies of ancient people were divided. It turned out that the Neanderthals from Vindia separated from modern humans — Homo sapiens — 520-630 thousand years ago, and from another subspecies of extinct humans, Denisovans — 390-440 thousand years ago.
The researchers also found mutations in the genome of a Neanderthal woman associated with susceptibility to diseases found in modern humans. Among them were variants associated with eating disorders, rheumatoid arthritis and schizophrenia. Some gene variants are associated with the level of low-density cholesterol ("bad" cholesterol) and vitamin D in blood plasma, as well as a reaction to antipsychotic drugs. According to the authors of the work, their results were another proof that Neanderthal variants of genes affect the risk of certain diseases in modern humans.
Neanderthals lived in Europe, the Middle East and Central Asia in the period 600-25 thousand years ago. Scientists offer different hypotheses explaining why Neanderthals became extinct. According to one version, they were mowed down by diseases that people brought from Africa; according to another, they died out during the last ice age due to climate change and the inability to make warm clothes. Perhaps their small number played a role: Neanderthals experienced the "bottleneck effect" for a long time and accumulated harmful mutations that affected the viability of the population.
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