For more than 10,000 years, Tibetan women living on the high Tibetan Plateau have not only survived but thrived despite the challenges of breathing thin air.
At these extreme altitudes, there is much less oxygen, making it harder for people to get the oxygen they need with every breath.
However, these women have adapted over generations to live and reproduce in this low-oxygen environment.
A recent study led by Cynthia Beall, a professor emerita from Case Western Reserve University, sheds light on how Tibetan women have developed unique physiological traits that help them thrive at high altitudes.
The study, published in the Proceedings of the National Academy of Sciences, focused on how these adaptations enhance their reproductive success.
Beall and her research team studied 417 Tibetan women between the ages of 46 and 86, living at elevations between 12,000 and 14,000 feet in a region of Upper Mustang, Nepal.
The researchers collected information about the women’s reproductive histories, measured their physical traits, took DNA samples, and considered social factors.
The goal of the study was to understand how certain physiological traits that help with oxygen delivery might be linked to the number of live births—a key measure of survival and adaptation in such challenging conditions.
The study found that women who had the most children shared a specific combination of blood and heart traits that helped their bodies deliver oxygen efficiently.
Their hemoglobin levels, which help carry oxygen in the blood, were near the average for the group.
However, these women had higher oxygen saturation levels, meaning their bodies were better at delivering oxygen to their cells.
This efficient oxygen delivery helped them avoid the strain of thickening blood, which can put extra pressure on the heart.
“This shows how natural selection is still ongoing,” said Beall. “Tibetan women have evolved to balance their oxygen needs without overworking their hearts.”
The study also discovered that a genetic trait likely inherited from an ancient human species called the Denisovans, who lived in Siberia 50,000 years ago, played a role in this adaptation.
This genetic variant, known as EPAS1, is unique to populations on the Tibetan Plateau and helps regulate hemoglobin levels. In addition, other traits like increased blood flow to the lungs and larger heart ventricles further supported oxygen delivery.
Beall’s interdisciplinary research team included collaborators from the Case Western Reserve School of Medicine and other international researchers.
They conducted their fieldwork in 2019, working closely with local communities in the Nepal Himalayas. The team hired local women as research assistants and collaborated with community leaders to ensure a successful study.
The findings from this study not only highlight the remarkable resilience of Tibetan women but also provide valuable insights into human adaptation. This research could help scientists understand how humans might respond to extreme environments and low oxygen levels, both now and in the future.
By understanding these adaptations, scientists gain a deeper appreciation of human evolution and how populations can thrive in even the most challenging conditions.
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