Researchers found that Tibetan women who had the most children had higher blood oxygen levels than those who did not.
- A new study from Case Western Reserve University reveals a link between oxygen intake and reproductive success among women living on the Tibetan high plateau.
- The researchers noticed that women with the most children had higher blood oxygen saturation than others.
- This trait is linked to a variant of the EPAS1 gene. It could be descended from Denisova Man who lived in Siberia around 50,000 years ago.
As altitude increases, the amount of oxygen decreases making living conditions more difficult for humans. And yet, Tibetan women manage to carry life even though they live at very high altitude.
Researcher Cynthia Beall of Case Western Reserve University and her team tried to unlock the secrets of the fertility of these women who live in extreme conditions. They discovered that they have physiological traits boosting their ability to reproduce in a low-oxygen environment.
Reproduction at high altitude: Tibetan women have higher oxygen saturation
To understand how humans have managed to have offspring in the heart of the Tibetan mountains for more than 10,000 years, researchers followed 417 Tibetan women aged 46 to 86 who live between 3,600 and 4,200 meters above sea level. in a place located in the Kingdom of Mustang in Nepal, at the southern end of the Tibetan plateau. They recorded the number of children delivered, their pregnancy history as well as physiological measurements. They also took DNA samples.
By studying the data collected, scientists discovered that women who had the most children had a unique set of blood and heart traits that helped their bodies provide oxygen. They had levels of hemoglobin (the molecule that transports oxygen) close to average. On the other hand, their oxygen saturation was higher. For them, this specificity allows “more efficient delivery of oxygen to cells without increasing the viscosity of the blood: the thicker the blood, the more tense the heart is”.
“This is a case of natural selection in progress”explains Cynthia Beall in a press release. “Tibetan women have evolved in a way that balances the body’s oxygen needs without overtaxing the heart.”
Oxygenation: a genetic trait that comes from Denisova Man
In their article published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) on October 21, 2024, the researchers specify that the genetic trait is a variant of the gene EPAS1 which is unique to indigenous populations of the Tibetan Plateau and regulates hemoglobin concentration. They argue that the latter must have descended from Denisova Men, an extinct species of the genus Homo who lived in the Altai Mountains in Siberia around 50,000 years ago.
Other traits, such as increased blood flow to the lungs and larger heart ventricles, also contribute to improved oxygen delivery. “These traits have contributed to greater reproductive success, providing insight into how humans adapt to low oxygen levels in the air and their bodies throughout their lives“, conclude the authors.