Inhabitants of the Tibetan Plateau have evolved over thousands of years to thrive in low-oxygen environments, according to a new study. Researchers reveal that the adaptation allows Tibetans to survive despite the harsh conditions at high altitudes, where most people would struggle with hypoxia due to the thinner air.
The study, led by Cynthia Beall, an anthropologist and University Professor Emerita at Case Western Reserve University, was published on Oct. 21 in the Proceedings of the National Academy of Sciences (PNAS). It highlights the unique physiological traits of Tibetan women that have evolved over millennia to enhance their reproductive success in oxygen-poor environments.
Beall's research focuses on the impact of low-oxygen conditions on human biology, specifically the physiological differences between Tibetan women and non-native high-altitude residents. The study emphasizes the evolutionary traits that help Tibetan women give birth to healthier babies and have greater reproductive success, even in an environment where oxygen levels are dangerously low.
"Adaptation to high-altitude hypoxia is fascinating because the stress is severe, experienced equally by everyone at a given altitude, and quantifiable. It is a beautiful example of how and why our species has so much biological variation," Beall told ScienceAlert.
The study found that Tibetan women have a lower concentration of hemoglobin, higher oxygen saturation in hemoglobin, and greater blood flow in the uterine artery. These traits contribute to healthier pregnancies and heavier newborns, which is critical in a region where oxygen deprivation can lead to serious health complications.
Natural selection appears to have favored these traits among Tibetan women, increasing their reproductive success over generations. Beall explained that certain oxygen transport traits—such as higher oxygen saturation—offer significant benefits in the harsh Tibetan environment. Women with intermediate levels of hemoglobin, for instance, had better reproductive outcomes than those with very high or low levels.
"Previously we knew that lower hemoglobin was beneficial, now we understand that an intermediate value has the highest benefit," Beall said. "The higher the oxygen saturation, the more beneficial it is for reproductive success. The number of live births quantifies the benefits."
The study also revealed that even women with less optimal oxygen transport traits could still have many successful pregnancies if other traits, like oxygen saturation, were favorable.
