The evolution of our species is often symbolized as a four-legged chimpanzee slowly transforming into an upright hunter. But our story doesn’t end there. Today, evidence suggests that humans are still evolving, and it shows in our own physiology: from our skin to our eyes to our blood. Take, for example, our intestine. It contains one of the strongest documented examples of modern natural selection that scientists have yet found. About 10,000 years ago, humans in some parts of the world began domesticating cows and other herbivorous animals. Then, they learned to milk these animals. But the problem was that the intestines of adult mammals were not prepared for lactose. However, some of our ancestors had genetic variants that meant they could tolerate dairy without getting sick. That made the difference. Modern genetic studies in Europe, East Africa, and the Middle East suggest that, over time, lactose tolerance variants spread through natural selection. Today, that’s probably why 30 to 35 percent of the world’s adult population can tolerate lactose. Meanwhile, in the Andes of South America, it is not milk but the potato that has shaped the evolution of the human intestine. Potatoes are a common staple food in Peru. (maphke/iStock/Getty Images) The highland Quechua people of indigenous Andean descent were among the first in the world to domesticate the potato. Earlier this year, researchers discovered that this population appears to be better equipped for starch digestion than almost any other on Earth. “Biologists have long suspected that different groups of humans have evolved genetic adaptations in response to their diets,” said evolutionary anthropologist Omer Gokcumen of the University at Buffalo. “But there are very few cases where the evidence is this strong.” When the ancestors of indigenous Andean people began growing potatoes, those with a higher number of copies of a given genetic variant likely gained an evolutionary advantage. As of about 10,000 years ago, those with about 10 or more copies had a survival or reproductive advantage of 1.24 percent per generation. That’s small, but it’s enough to add up over the millennia.” “Humans in the Andes appear to have developed an unusual genetic capacity. Adaptations to our environment also run through our veins. Take humans living on the Tibetan plateau as an example. Here, high-altitude living for more than 10,000 years has led to fascinating adaptations among local communities. For years, anthropologist Cynthia Beall of Case Western Reserve University in the US has been studying how the human body responds to a lack of oxygen at high altitude. In 2024, she and her team reported evidence showing that Tibetan communities possess adaptive traits that improve their blood’s ability to deliver oxygen. selection,” Beall said at the time. frameborder=”0″ enable=”accelerometer; autoplay; write to clipboard; encrypted media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” enablefullscreen> The example is especially strong given the association with playback. Among 417 Nepalese women who had lived their entire lives at altitudes above 3,500 meters (11,480 feet), those who demonstrated the highest live birth rate showed red blood cells with unusually high oxygen saturation. “We knew that higher oxygen saturation of hemoglobin was beneficial; “We now understand that the higher the saturation, the more beneficial,” Beall told ScienceAlert’s Michelle Starr. “The number of live births quantifies the benefits.” Non-invasive measurement of hemoglobin concentration and oxygen saturation. (Sienna R. Craig) Some signs of natural selection can also be seen on the outside of our bodies. Skin pigmentation, for example, is a commonly used example cited from our species’ adaptation to sun exposure. It is widely accepted that early humans in Africa had darker skin because it provided protection against DNA damage caused by strong ultraviolet radiation. But farther from the equator, selective pressures appear to favor lighter skin. A map showing global differences in ultraviolet (UV) radiation, human skin pigmentation, and genes associated with skin color. historical and gene flow between populations (Liu et al., Molecular Ecology, 2024) This year, the largest ancient DNA data set yet revealed evidence of natural selection among Western Eurasians. Nearly 500 genetic variants were identified in this lineage that had changed in the last 10,000 years. The strongest evolution in the data set concerned skin pigmentation. Over the past 10,000 years, the results suggest that genetic variants associated with lighter pigmentation have become more common in this human population. “It plausibly reflects selection for greater synthesis of vitamin D in regions with little sunlight in farmers with little in their diets,” the authors suggest. Even the way you are reading this article right now could be a product of natural selection. Myopia has increased in recent decades. In 2021, researchers found evidence in the UK Biobank that the condition is associated with mutant alleles. These alleles have increased in frequency over the last 25 years, possibly because of natural selection. While myopia could be a disadvantage for survival, some of the genetic variants linked to this trait may have other advantages for reproduction. argues that certain genes confer beneficial effects early in life, but cause detrimental effects later. “We estimate that, in the United Kingdom alone, natural selection adds more than 100,000 cases of myopia per generation, and we argue that antagonistic pleiotropy should be widely considered in humans and beyond,” the authors of the 2021 study concluded. Evolution does not always make us healthier. or in better shape. Related: The ‘shadow’ in evolution that explains why long life has a cost Natural selection favors genes that help us survive, but sometimes, they can carry other traits that are not so advantageous. As the modern world continues to change shape around us, so will the evolutionary pressures that shape our species. Human evolution is far from over. This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. While we take pride in our process, we’re only human. If you spot an error, please let us know.
