Human Evolution Unfolding In The High Altitudes Of Tibetan Plateau

In order to survive in the low oxygen conditions of the Tibetan Plateau, people living there have evolved special adaptations over the course of more than 10,000 years, according to a new study. The Tibetan communities have adapted to survive and flourish in spite of the thinner air, which contrasts with most people who would suffer from hypoxia. This illustrates how humans continue to evolve in response to challenging living situations.

This phenomenon is clarified by the research conducted by Cynthia Beall, a University Professor Emerita at Case Western Reserve University. The study, which was published on October 21 in the Proceedings of the National Academy of Sciences (PNAS), shows how the physiological characteristics of Tibetan women enhance their capacity to procreate in an oxygen-poor environment.

"Adaptation to high-altitude hypoxia is fascinating because the stress is severe, experienced equally by everyone at a given altitude, and quantifiable," anthropologist Cynthia Beall of Case Western Reserve University in the US told ScienceAlert. "It is a beautiful example of how and why our species has so much biological variation."

When comparing the pregnancy-related biology of Tibetan women with that of migrants to high altitudes, Tibetan women have lower hemoglobin concentration, higher oxygen saturation of hemoglobin and uterine artery blood flow, and heavier newborns. Among Tibetan women who have completed childbearing, unelevated hemoglobin concentration, higher oxygen saturation, and a higher pulse rate correlate with higher lifetime reproductive success. This pattern of human variation suggests the action of natural selection on oxygen delivery phenotypes.

"Previously we knew that lower hemoglobin was beneficial, now we understand that an intermediate value has the highest benefit. We knew that higher oxygen saturation of hemoglobin was beneficial, now we understand that the higher the saturation the more beneficial. The number of live births quantifies the benefits," Beall said.

"It was unexpected to find that women can have many live births with low values of some oxygen transport traits if they have favorable values of other oxygen transport traits."