Natural selection is currently unfolding in these remote villages in Nepal

Natural selection is taking place among humans right now – high in the mountains of Nepal, scientists have discovered.

The new research suggests that ethnic Tibetan women, who are physiologically better adapted to living in low-oxygen conditions at high altitudes, are having more children than their peers. This indicates that these beneficial traits are currently being ‘selected’, meaning there is an evolutionary pressure to pass them on to the next generation.

In other words, natural selection happens.

The researchers revealed their findings in a study published Oct. 21 in the journal PNAS. The study examined more than 400 women, aged 46 to 86, living in villages in the Upper Mustang District of Nepal, on the border with Tibet. The villages are 11,500 to 13,500 feet (3,500 to 4,100 meters) above sea level.

People living at high altitudes face harsh environmental conditions, including low air pressure reduces the amount of oxygen available in 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 diseases such as: acute mountain sickness or cerebral edema at high altitudein which the brain swells.

Low-oxygen environments are especially challenging for pregnant women at higher altitudes, due to an increased risk of preeclampsiaa potentially fatal blood pressure condition, and is more likely to cause babies to be born low birth weight. Therefore, in populations living at high altitudes, there may be strong selective pressure for traits that help increase survival, both during and after pregnancy.

Previous research has shown that Tibetans have done so physiological distinguishing features And versions of genes which help them survive in low-oxygen environments more easily than people without these characteristics. In the new study, researchers wanted to see if they could link these genetic and physiological traits to reproductive success to show that evolution occurs through natural selection in these populations.

In biology, ‘reproductive success’ is usually measured by the number of offspring an organism has produced, because that reflects the number of times they have passed on their genes. That is why the researchers kept track of how many children the women in these villages had given birth to. They also took several physiological measurements and analyzed those of the women DNA.

Computer-generated image of red blood cells traveling through blood vessels.

The new study found that Tibetan women who were able to more efficiently deliver oxygen to their tissues through their blood also had more children than others. (Image credit: Roger Sutcliffe via Getty Images)

They found that the women who had the most children had typical levels of childbearing hemoglobin — the blood responsible for transporting oxygen. But their hemoglobin was able to carry more oxygen than women who had fewer children.

In addition, the women with more children had greater blood flow to their lungs. And their left ventricles – the chamber of the heart pumps oxygen-rich blood to the body – were wider than those with fewer children. A wider ventricle means that more oxygen-rich blood can reach a person’s tissues in a given heartbeat.

In a separate analysis, researchers found that about 80% of women in the study carried a version of a gene known as EPAS1, which is thought to lower hemoglobin concentrations in the blood. This may seem counterintuitive, because less hemoglobin means you can’t carry as much oxygen in the blood. However, too much hemoglobin can thicken the blood, making people vulnerable to developing a condition known as hemoglobin chronic mountain sickness.

The fact that the EPAS1 variant is so common suggests that there is a lot of pressure to pass this version of the gene from one generation to the next.

These new findings shed light on how evolution and adaptation occur in humans, study co-author Cynthia Bealla professor emerita of anthropology at Case Western Reserve University in Ohio told LiveScience. The findings could also have applications in medicine – for example, they could potentially provide insight into diseases linked to low oxygen levels, such as asthma and other lung conditions, she suggested.

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