New Delhi: Tibetan women in the high Tibetan Plateau have not only subsisted but have successfully reproduced for over 10,000 years in a low oxygen condition. A recent study by Distinguished University Professor Emerita Cynthia Beall of Case Western Reserve University shows how these women have adapted to develop special genetic and physiological adaptations for high-altitude survival and reproduction. The research is published in PNAS and helps to reveal more about the need for the EPAS1 gene variant and particular blood factors that support oxygen transport under severe conditions.
Inhaling thin air is difficult at high altitudes, especially above 12,000 feet, because the air is much thinner. However, the indigenous women of the Tibetan Plateau are far from fragile; they are evolutionarily conditioned survivors. Beall and her team recruited 417 women from the Tibetan population of Upper Mustang, Nepal, aged between 46 and 86 years old, living at altitudes of 12000–14000 feet. They collected information on the women’s previous pregnancies, their physical characteristics, blood types, and social demographics, hoping to determine how oxygen-carrying traits affected reproductive rates, which are considered a measure of the women’s evolutionary fitness.
This research revealed that those women who have the largest number of children have the particular blood and heart characteristics that allow for the maximum oxygen-carrying capacity without overloading the heart. Even though their haemoglobin levels were only average, they had higher oxygen saturation, which allowed for better oxygen delivery to the cells without raising the viscosity of the blood, which in turn would put extra work on the heart.
Natural Selection in Action
“This natural selection process continues to this date and shows how the Tibetan women have adapted to meet their oxygen requirements without stressing the heart, according to Beall. These adaptations are reflective of an ongoing process of natural selection of hypoxic-enhancing traits that would favour reproductive success. Oxygen delivery efficiency was most pronounced in women with improved heart function and the highest saturation, which influenced the reproductive success of those women.
A glance at the Genes of the Ancient Ancestors
The research team from Case Western Reserve School of Medicine and other international colleagues have established a genetic factor—the EPAS1 gene variant—presumably derived from the Denisovans, a type of archaic human who lived about 50,000 years ago. This gene helps adjust the concentration of haemoglobin, and coupled with increased lung blood flow and larger heart ventricles, the woman is able to deliver oxygen effectively even in low-ooxygen environment.
These results suggest that the Tibetan women are very adaptable to the harsh environment and have important implications for the study of human evolution and adaptation to the changing environment.
