Women living on the Tibetan Plateau have adapted to the low-oxygen environment for thousands of years through various evolutionary changes.
A study published in the journal PNAS by Cynthia Beall, a professor at Case Western Reserve University, reveals the adaptations that enable Tibetan women not only to survive but also to thrive in the harsh mountain environment. Breathing thin air at high altitudes poses a survival challenge, but the research indicates that the unique physiological traits of Tibetan women have improved their reproductive capabilities despite the low oxygen levels in their surroundings, according to Sci Tech Daily.
Tibetan women develop various adaptations to the low-oxygen environment. (Photo: iStock)
Beall and her colleagues studied 417 Tibetan women aged 46 to 86 living at altitudes of 3,657 – 4,267 meters above sea level in Upper Mustang, Nepal, located on the southern edge of the Tibetan Plateau. They gathered data on the women’s reproductive history, measured their physiology, collected DNA samples, and assessed social factors. Their goal was to understand how oxygen delivery characteristics that counteract hypoxemia at high altitudes affect birth rates, a key measure of evolutionary fitness.
The researchers found that a significant number of children exhibited a range of unique blood and heart characteristics that enhance oxygen transport. The women with the highest birth rates had hemoglobin levels (the oxygen-carrying molecule) close to the average of the sample population but had much higher oxygen saturation, allowing for more efficient oxygen delivery to cells without increasing blood viscosity.
“This is a case of ongoing natural selection. Tibetan women are evolving in a way that balances their body’s oxygen needs without overworking the heart,” Beall commented.
Beall’s interdisciplinary research team includes Brian Hoit and Kingman Strohl from Case Western Reserve School of Medicine and several other international scientists, who conducted field surveys in 2019. They actively engaged with the local community in the Himalayan region of Nepal, employing local women as research assistants and collaborating with many community leaders.
One genetic trait they investigated likely originates from Denisovans who lived in Siberia around 50,000 years ago. The descendants of Denisovans later migrated to the Tibetan Plateau. This trait is a variant of the EPAS1 gene, which is found only in indigenous communities on the Tibetan Plateau, helping to regulate hemoglobin levels. Other traits, such as increased blood flow to the lungs and a larger ventricular chamber, also enhance oxygen transport. These features contribute to greater reproductive success, providing insight into human adaptation to low oxygen levels throughout life.
