Imma Perfetto
Cosmos science journalist
Researchers have found the body traits which help ethnic Tibetan women reproduce in the oxygen-scarce, highest region on Earth.
Women with the most live births had a combination of blood and cardiovascular characteristics which enhance oxygen delivery to the body’s tissues.
“Understanding how populations like these adapt gives us a better grasp of the processes of human evolution,” says Cynthia Beall of Case Western Reserve University in the US, who led the study.
Insights into the ways humans can adapt to extreme environments can also offer clues to how we might respond to future environmental challenges.
The 417 women included in the study were aged 46 to 86 and lived more than 3,500m above sea level in the Upper Mustang District of Nepal, on the border of Nepal and the Tibet Autonomous Region.
To study the women, who self-identify as ethnically Tibetan, Beall and colleagues worked closely with local communities in the Nepal Himalayas, ethnic Tibetan female nurses and research assistants from Nepal.
They collected data on the women’s reproductive histories, physiological measurements, DNA samples and social factors to examine whether traits related to oxygen delivery in the body in the face of high-altitude hypoxia (low levels of oxygen in the air and the blood) influenced reproductive success across their lifetimes.
But as a result of wishes expressed by the women in community engagement prior to starting fieldwork, they did not collect blood samples but used a non-invasive fingertip device.
Women reporting the most live births had about average levels of haemoglobin, the molecule that carries oxygen in the blood, but had higher blood oxygen saturation. This allows more efficient oxygen delivery to cells without increasing the thickness of the blood, which places more strain on the heart.
“This is a case of ongoing natural selection,” says Beall.
“Tibetan women have evolved in a way that balances the body’s oxygen needs without overworking the heart.”
In addition, traits such as high blood flow into the lungs, wide left ventricles of the heart, and low hypoxic heart rate responses helped these women effectively transport oxygen to their tissues.
The study appears in the journal Proceedings of the National Academy of Sciences.