A new study suggests that, compared with their peers, ethnic Tibetan women who are physiologically better adapted to living in low-oxygen conditions at high altitudes are having more children. This suggests that these beneficial traits are being \u201cselected for,\u201d meaning there is evolutionary pressure to pass them on to the next generation.<\/p>\n
In other words, natural selection occurs.<\/p>\n
The researchers presented their findings in a study published Oct. 21 in the journal PNAS. The study involved more than 400 women aged 46 to 86 living in villages in Nepal’s Upper Mustang region, bordering Tibet. The villages are located at elevations ranging from 11,500 to 13,500 feet (3,500 to 4,100 meters) above sea level.<\/p>\n
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People living at high altitudes face harsh environmental conditions, including low air pressure, which reduces the amount of oxygen available to the body. These low oxygen levels can cause tissues to stop functioning, leading to symptoms such as confusion and difficulty breathing. In more severe cases of this condition, called hypoxia, people can develop fatal illnesses such as acute mountain sickness or high-altitude cerebral edema, in which the brain swells.<\/p>\n
Low-oxygen environments are particularly challenging for pregnant women at high altitudes due to an increased risk of preeclampsia, a potentially fatal blood pressure condition, and a higher likelihood of having low-birth-weight babies. Thus, in populations living at high altitudes, there may be strong selective pressure for traits that help improve survival, both during and after pregnancy.<\/p>\n
Previous studies have shown that Tibetans have physiological traits and versions of genes that help them survive in low-oxygen environments more easily than people without these characteristics. In the new study, the researchers wanted to see if they could link these genetic and physiological traits to reproductive success to show that evolution is occurring through natural selection in these populations.<\/p>\n
In biology, \u201creproductive success\u201d is typically measured by counting how many offspring an organism produces, since this reflects the number of times they pass on their genes. So the researchers recorded how many children the women in these villages had. They also took various physiological measurements and analyzed the women\u2019s DNA.<\/p>\n
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They found that women who had the most children had typical levels of hemoglobin, the element in the blood that carries oxygen. But their hemoglobin was able to carry more oxygen than women who had fewer children.<\/p>\n
What’s more, women with more children had more blood flow to their lungs. And their left ventricles \u2014 the chambers of the heart that pump oxygenated blood around the body \u2014 were wider than those of women with fewer children. A wider ventricle means more oxygenated blood can get to a person’s tissues in a single heartbeat.<\/p>\n
In a separate analysis, the researchers found that about 80% of the women in the study carried a version of a gene known as EPAS1, which is thought to lower the concentration of hemoglobin in the blood. This may seem counterintuitive, since low hemoglobin levels mean you can\u2019t carry as much oxygen in your blood. However, too much hemoglobin can thicken the blood, making people vulnerable to developing a condition known as chronic mountain sickness.<\/p>\n
The fact that the EPAS1 variant is so common suggests that there is a high burden of passing this version of the gene from generation to generation.<\/p>\n
Papua New Guineans, genetically isolated for 50,000 years, carry Denisovan genes that help their immune systems, research suggests.<\/strong><\/span><\/p>\n Genes inherited from Denisovans, extinct human relatives, may help lowlanders in Papua New Guinea fight infections, while mutations in red blood cells may help highlanders survive at high altitudes.<\/p>\n The people of Papua New Guinea, who were genetically isolated for millennia, carry unique genes that help them fight infections, and some of these genes come from our extinct human cousins, the Denisovans.<\/p>\n The study also found that highland and lowland inhabitants developed different mutations that helped them adapt to very different environmental conditions.<\/p>\n “New Guineans are unique because they have been isolated since they settled in New Guinea more than 50,000 years ago,” one of the study’s senior authors, Fran\u00e7ois-Xavier Ricaud, a biological anthropologist at the French National Center for Scientific Research (CNRS), told Live Science in an email.<\/p>\n Not only is the island nation’s predominantly mountainous terrain particularly challenging, but infectious diseases account for more than 40% of deaths.<\/p>\n So local people had to find a biological and cultural strategy for adaptation, which means Papua New Guinea’s population is a “fantastic cocktail” for studying genetic adaptation, Rico said.<\/p>\n\n Modern humans first arrived in Papua New Guinea from Africa about 50,000 years ago. There, they interbred with Denisovans, who had lived in Asia for tens of thousands of years. As a result of this ancient interbreeding, Papua New Guineans contain up to 5% Denisovan DNA in their genomes.<\/p>\n In a new study published April 30 in the journal Nature Communications, scientists analyzed the genomes of 54 highlanders from Mount Wilhelm, who lived at elevations between 7,500 and 8,900 feet (2,300 and 2,700 meters) above sea level, and 74 lowlanders from Daru Island, who lived at elevations less than 330 feet (100 meters) above sea level.<\/p>\n They found that mutations that lowlanders likely inherited from the Denisovans increased the number of immune cells in their blood. Highlanders, meanwhile, developed mutations that increased the number of red blood cells in their blood, which helps reduce hypoxia at altitude. This isn\u2019t unusual, as people from several other high-altitude environments have developed different mutations to combat hypoxia.<\/p>\n Variants in the Denisovan genes may affect the function of a protein called GBP2, which helps the body fight pathogens that are only found at lower altitudes, such as the parasite that causes malaria. So these genes may have been selected during evolution to help humans fight infection at lower altitudes where pathogens are common, the team said.<\/p>\n Next, the team wants to figure out how these mutations cause changes in the blood of Papua New Guineans, Rico said. To decipher that, they will need to study how these mutations affect the activity of the genes in which they are found.<\/p>\n Natural selection has acted on hundreds of human genes over the past 3,000 years. New research shows that human ingenuity has not exempted us from the forces of evolution.<\/strong><\/span><\/p>\n New research shows that natural selection \u2013 the evolutionary process that determines which traits become more common in a population \u2013 has been acting on us for the past 3,000 years, right up to the present day.<\/p>\n And it appears to have surprising effects on complex traits coded by multiple genes, such as those linked to intelligence, mental illness and even cancer.<\/p>\n In natural selection, genes that provide some advantage in survival or reproduction are passed on and persist in a population, while those that result in decreased survival or fewer offspring become less common. There is no doubt that natural selection has shaped human evolution in our more distant past. But the impact of natural selection in the recent past is a much more contentious issue.<\/p>\n The new study suggests that natural selection is indeed an important factor in the modern era, although the methods used in the study have been flawed in the past, said John Novembre, a computational biologist at the University of Chicago who was not involved in the new study. That means the results should not be taken as the final word on modern natural selection.<\/p>\n The new study focuses on traits that arise from combinations of multiple gene variants, such as intelligence and skin pigmentation. The complex genetics of these traits makes it difficult to decipher the effects of individual genes. To detect these subtle effects, researchers conduct genome-wide association studies (GWAS), in which they scan genetic markers across the genome to find short genetic sequences that are more common in certain traits than others.<\/p>\n These results can be difficult to interpret, even when comparing people at the same point in time. New research ups the ante by looking not just at the genes associated with complex traits, but also at the signs of natural selection on those traits. Essentially, genes that become more common over time are under positive selection: They are beneficial in some way and are thus more likely to be passed on. Genes that become less common over time are under negative selection. They are somehow harmful to survival or reproduction and are thus less likely to be passed on.<\/p>\n In their study, published November 15 in the journal Nature Human Behaviour, the scientists found a total of 755 traits that showed signs of selection over the past 2,000 to 3,000 years.<\/p>\n For the modern samples, the researchers used data from people of European descent in the UK BioBank, a repository of genetic and medical data from 500,000 participants. To delve deeper into history, the researchers also used three sets of ancient human DNA from the pre-Neolithic, Neolithic and post-farming Middle East, totaling 512 people. The researchers looked at three time periods: the modern era, the last 2,000 to 3,000 years and up to about 100,000 years ago. The oldest data is the most unreliable, said study leader Guan Ning Lin, a professor in the School of Biomedical Engineering at Shanghai Jiaotong University.<\/p>\n\n Although the researchers had detailed health and lifestyle information from the UK BioBank, they only had partial genetics for older samples and no direct information on things like how many children a person had or what they ate. So they used the genes themselves to infer traits. If a gene known to be involved in height increased in frequency over time, the researchers took that as a signal that height might be under positive natural selection.<\/p>\n The traits that appeared to be under selection ranged from skin features such as \u201ceasiness to tan\u201d to various body measurements. Somewhat surprisingly, genes linked to some seemingly undesirable traits became more common over time, including genes linked to conditions such as skin cancer, inflammatory bowel disease and anorexia nervosa. This suggests that some of these disorders arise as side effects of genes that are beneficial for other reasons, the researchers suggested.<\/p>\n Ling and his colleagues were most interested in the question of why disorders with complex genetics, such as schizophrenia or attention deficit hyperactivity disorder (ADHD), persist despite natural selection.<\/p>\n One of the biggest problems is something called \u201cstratification.\u201d Differences between two populations can appear to be genetic when they are actually environmental. Because GWAS can\u2019t show that a gene causes a trait, only that they are linked, the results can quickly get weird. To use a classic example from a 1994 paper, chopstick-using skills are clearly not a gift from DNA: they are a matter of practice from an early age. But a GWAS study in a diverse population like San Francisco could very easily find evidence of genes associated with chopstick-using skills simply by identifying genes that are more common in East Asian populations than in European populations.<\/p>\n This mistake did happen. Over the past decade, several papers have appeared claiming that variations in genes that control height are more common in northern Europe than in southern Europe, and that natural selection is pushing northern Europeans to be taller on average, according to a 2012 study published in the journal Nature Genetics.<\/p>\n But it turns out that the influence of these genetic variants was overestimated, Novembre said. When looking at the same genetic variants in less diverse populations (a strategy to reduce the stratification problem), the evidence for natural selection disappeared. The study identified previously unknown environmental differences between northern and southern Europeans and mistakenly assumed they were purely genetic. The researchers had to completely rethink the results, and they\u2019re still unsure whether natural selection has anything to do with the height differences across Europe, according to a 2019 paper in the journal eLife.<\/p>\n Using only people of European descent helps limit the stratification problem. But there is still potential for a stratification problem to arise.<\/p>\n Among the hundreds of traits that the researchers found may be subject to natural selection, a few stood out. Focusing on contemporary data, the researchers found that higher IQ was associated with more sexual partners but fewer children. Meanwhile, ADHD and schizophrenia were also associated with more sexual partners. These two conditions are examples of traits that may be problematic in everyday life but improve mating success.<\/p>\n Looking back over more than 100,000 years of human history, the researchers found that traits related to skin tone and body size were the most likely to show selection pressure. These include things like facial size, height, and torso length. For example, genes related to facial shape and size appear to have been under natural selection over the past 100,000 years, the researchers found, which may be linked to changes in the jaw and skull related to diet and brain growth.<\/p>\n Looking back 3,000 years, the researchers found that inflammatory bowel disease appeared to be favored by natural selection. This could be an example of a trait that is beneficial in one context and harmful in another, Lin said.<\/p>\n But it can be very difficult to show why a particular trait is associated with evolutionary success. To use height as an example, being tall might benefit reproduction by making someone more attractive to potential sexual partners. Or perhaps height is simply a side effect of an efficient metabolism that improves survival rates, and that the increased likelihood of surviving to reproductive age can lead to genes being passed on to the next generation. If genes tend to change together \u2014 and many do \u2014 natural selection may act on an entirely different trait than the one that seems most intuitive. For example, variants that make skin easier to tan, which were found to be highly selected for in the new study, are likely associated with many other traits, such as rates of skin cancer, freckles, and hair color. It\u2019s hard to know exactly which pathway leads to someone reaching reproductive age, attracting a fertile partner, and having lots of children, and which genes are just lucky hangers-on in the process.<\/p>\n To complicate matters, there are cases where the genetics of a trait can be completely overwhelmed by the environment. Something similar could theoretically happen with human intelligence. IQ is partly heritable, so if it is true that people with higher IQs have fewer children, that might lower the collective IQ of the population over time. But if the environment becomes more conducive to brain development\u2014better nutrition, less lead or other pollutants\u2014the population might well become smarter.<\/p>\n One approach to identifying natural selection would be to combine large-scale GWAS with studies of the genomes of individual families. Family members, especially siblings, tend to grow up in fairly similar environments, making it easier to tell when genes influence a particular trait. These family studies can be used to test the claims made by large GWAS samples, figuring out which genes still have an effect when as many environmental factors as possible are removed from the equation.<\/p>\n The scientists plan to conduct family studies to learn more about the genetics of complex conditions like schizophrenia. They are also working to quantify genetic variants that can cause both beneficial and harmful effects, he said. The new study\u2019s findings are a starting point and a reminder that natural selection is still a force in human biology.<\/p>\n\n","protected":false},"excerpt":{"rendered":" Scientists have discovered that natural selection is happening right now among humans high in the mountains of Nepal. The physiological traits that help Tibetan women survive at high altitude are being selected for within the population, meaning they could become more common. The people of Papua New Guinea, who have been genetically isolated for millennia, carry unique genes that help them fight off infections, and some of these genes come from our extinct human cousins, the Denisovans.…<\/p>\n![\"\"](\"https:\/\/planeta21vek.ru\/artemiada\/wp-content\/uploads\/2024\/11\/papua241124.jpg\")
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