A recent study reveals that Tibetan communities have evolved unique physiological adaptations over more than 10,000 years, enabling them to survive and flourish in the harsh, oxygen-poor environment of the Tibetan Plateau. This discovery highlights how human evolution continues to respond to challenging living conditions.
The research, led by Cynthia Beall, University Professor Emerita at Case Western Reserve University, was published on October 21 in the Proceedings of the National Academy of Sciences (PNAS). It explores how Tibetan women have evolved to improve their reproductive success despite the low oxygen levels at high altitudes, a condition known as hypoxia, which affects most people living at such elevations.
“Adaptation to high-altitude hypoxia is fascinating because the stress is severe, experienced equally by everyone at a given altitude, and quantifiable,” Beall told ScienceAlert. “It is a beautiful example of how and why our species has so much biological variation.”
The study compares the pregnancy-related biology of Tibetan women with that of migrants to high altitudes. It found that Tibetan women have lower hemoglobin concentrations, higher oxygen saturation of hemoglobin, and improved uterine artery blood flow, resulting in healthier newborns. These traits, shaped by natural selection, help them cope with the low oxygen environment.
For Tibetan women who have completed childbearing, those with intermediate hemoglobin levels, higher oxygen saturation, and elevated pulse rates tend to have more children. This suggests that these oxygen-delivery traits are beneficial for reproduction.
Beall explains, “We knew that lower hemoglobin was beneficial, but now we understand that an intermediate value has the highest benefit. Similarly, higher oxygen saturation of hemoglobin provides greater benefits. The number of live births quantifies these advantages.”
This study underscores the power of natural selection in shaping physiological traits that allow people living at high altitudes to thrive, illustrating the remarkable diversity in human biology.