Nepal’s Upper Mustang, on the edge of the Tibetan Plateau, is home to life in severely thin air. Here, oxygen levels drop to about 60% of what many people are used to. While visitors may experience headaches and fatigue, Tibetan women in this region are thriving—many even having large families.
A recent study in the Proceedings of the National Academy of Sciences highlights these women’s unique adaptations that enhance oxygen efficiency, leading to greater reproductive success under low-oxygen conditions. This research offers important insights into human evolution and how we might adapt to extreme environments in the future.
According to lead author Cynthia Beall, a professor emerita at Case Western Reserve University, this study helps us understand how natural selection operates today: “Understanding how populations like these adapt gives us a better grasp on human evolution.”
The research team analyzed 417 ethnic Tibetan women, aged 46 to 86, who live between 3,600 and 4,200 meters (over 11,800 feet). They measured each woman’s live births, oxygen levels, and heart structure, which helped reveal the connection between oxygen efficiency and reproductive success. The women with balanced hemoglobin levels had the most live births, averaging about 5.2 children each.
Beall noted that “higher oxygen saturation of hemoglobin was beneficial; the higher the saturation, the more beneficial.” These women also displayed features like larger left ventricles in their hearts, which aid in effective blood oxygenation without causing health issues typical of high altitudes, such as increased blood viscosity.
At the genetic level, a variant of the EPAS1 gene was key in their adaptations. Found mainly in Tibetans, this gene likely originated from Denisovans—an ancient human relative that interbred with modern humans over 50,000 years ago. The study confirmed that women carrying this gene variant had traits tied to high fertility and effective oxygen delivery.
As Beall stated, “Tibetan women have evolved to balance the body’s oxygen needs without overworking the heart.” This natural selection process is crucial for thriving in such extreme conditions.
Interestingly, adaptation to high altitudes isn’t exclusive to Tibetans. Indigenous Andean groups in Peru and Bolivia have adapted differently, primarily by having higher hemoglobin levels. While this can improve oxygen capacity, it also makes the blood thicker, which can strain the heart.
Tibetans, on the other hand, maintain normal or slightly lower hemoglobin levels. They have adapted with enhanced blood flow to the lungs, ensuring better oxygenation without the metabolic costs that other populations experience. This illustrates a fascinating example of convergent evolution, where different groups facing similar challenges develop distinct biological solutions to thrive.
Overall, the breakthroughs in understanding how Tibetan women adapt offer us a glimpse into ongoing human evolution. As we face new environmental challenges, these insights may help guide future adaptations.
For more on the latest scientific research, see the full study in PNAS.
