Inheritance with a burden
The genetic heritage of Neanderthals
A paper has been published in the journal Science, the authors of which tried to establish what genes inherited from Neanderthals give to modern people.
Maxim Russo, "Polit.<url>" based on the materials of Science: Our hidden Neandertal DNA may increase the risk of allergies, depression
In the genome of modern humans, there are a number of genes that penetrated there as a result of the meeting of our ancestors with Neanderthals. Two species (or, according to another version, two subspecies) interbred, giving viable offspring, and as a result, archaic variants of genes (alleles) from the Neanderthal genome penetrated into the genome of modern humans.
The work was published in the journal Science (Simonti et al., The phenotypic legacy of admixture between modern humans and Neanderthals), the authors of which tried to establish what genes inherited from Neanderthals give to modern humans. In a large-scale statistical study, they found that Neanderthal genes increase the risk of depression and allergies. But other studies have also found Neanderthal genes that have brought considerable benefits to people.
On average, the inhabitants of Europe and Asia have about 1.5% of the genome made up of Neanderthal genes. In the inhabitants of Melanesia, an additional 2 to 3% of the genes were obtained from the Denisovan man. Africans, as a rule, do not have Neanderthal genes, since the crossing of modern man with a Neanderthal occurred after modern humans left Africa. Comparing the genomes of several Neanderthals and one sample of the Denisov genome with modern ones, scientists have identified about 12 thousand Neanderthal variants of genes present in modern humans. To establish the exact function of these genes, expensive studies of gene expression in tissues or laboratory animals were required.
A way to get around this obstacle independently came up with geneticists Joshua Akey from Washington State University and Tony Capra from Vanderbilt University in Nashville. They decided to search for Neanderthal versions of genes in the Electronic Medical Records and Genomics (eMERGE) Network medical database. Covering residents of nine US cities, this database links information about their genomes with medical histories. As a result, researchers are able to track correlations between genes and disease symptoms in tens of thousands of people.
Joining forces, Eki and Capra analyzed more than 6,000 Neanderthal haplotypes among the genetic data of 28,416 adult Americans of European descent. As a result, they found about a dozen Neanderthal genes that are statistically associated with an increased risk of a number of disorders. For example, one variant of the gene increases blood clotting. Perhaps faster blood clotting during Neanderthal times reduced the risk of death from a wound when hunting large animals or during childbirth. But now such a gene increases the likelihood of blood clots and stroke.
A number of genes have been associated with neurological disorders, such as depression, which occurs when circadian rhythms are disrupted. Other Neanderthal genes are associated with precancerous skin conditions, so-called keratoses. Capra suggests that the genes responsible for brain chemistry and skin resistance to light radiation were tuned in Neanderthals to the conditions of prehistoric Europe, and now, when people spend a lot of time in artificial light, they act less adequately.
There are Neanderthal genes that regulate the transport of thiamine (vitamin B1), which is responsible for the metabolism of carbohydrates in the body. According to Capra, Neanderthals, who had a lot of meat and nuts in their diet, had enough thiamine, and when feeding modern people, it is often lacking. The study also revealed Neanderthal alleles associated with incontinence, pain in the bladder and urinary tract, and even a gene leading to a predisposition to nicotine addiction.
However, the influence of the Neanderthal genome on our health is not always negative. Two studies published last month in the American Journal of Human Genetics identified three archaic gene variants that boost the innate immune response that helps protect the body from bacteria and pathogenic fungi. All three genes, according to the lead author of one of the papers, Janet Kelso, a bioinformatics specialist from the Max Planck Institute for Evolutionary Anthropology, have spread widely among Europeans and Asians, encouraged by natural selection. According to the lead author of another paper, Lluis Quintana-Murci from the Pasteur Institute in Paris and the National Center for Scientific Research, these genes work together, regulating the expression of so-called toll-like receptors (toll-like receptors). These receptors are located on the surface of various types of cells of the immune system. They recognize various structures of microorganisms and activate the immune response.
Such an example shows that when modern people got into new conditions, where they met with new pathogens, they cut the evolutionary path by borrowing useful genes from close relatives – Neanderthals. Neanderthals had at least 200,000 years to adapt to living conditions in the Middle East and Europe before modern humans appeared there.
However, genes useful in the Pleistocene epoch and in modern Third world countries, where people live in difficult conditions, may be harmful to residents of the United States or Europe, who are less likely to encounter parasites and other pathogens. Janet Kelso and her colleagues found that archaic immune-stimulating gene variants are associated with a high risk of allergies. "The price we pay today for an enhanced immune response is the possible harm to us associated with autoimmune diseases, inflammation and allergies," says Lewis Kitana–Murchi.
How these genes functioned in the Neanderthal body is not entirely clear. Scientists warn that based on the data obtained, it is impossible to conclude that Neanderthals suffered from depression or had skin cancer. In the future, researchers plan to expand the search for Neanderthal alleles and compare them with even more extensive libraries of modern genomes, covering tens or even hundreds of thousands of people. They are confident that they will be able to find many more genetic heritage of Neanderthals.
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19.02.2015