New research explores the connection between oxygen delivery and reproductive success in Tibetan women
Living at high altitudes, where the air is thin and oxygen is scarce, poses a considerable challenge. Nevertheless, for over 10,000 years, women from the high Tibetan Plateau have not only survived but also flourished in these conditions.
A recent study conducted by Cynthia Beall, an esteemed professor emerita at Case Western Reserve University, addresses this phenomenon. Published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), the research highlights how the unique physiological traits of Tibetan women support their reproductive success in low-oxygen settings.
The research findings, according to Beall, not only highlight the extraordinary adaptability of Tibetan women but also offer significant insights into how humans can adjust to extreme environments. This kind of study can shed light on human development, our potential responses to future environmental challenges, and the underlying biological issues faced by people suffering from oxygen deficiency at all altitudes.
“Gaining a better understanding of how populations like these adapt,” Beall noted, “enhances our comprehension of human evolution processes.”
The research details
Beall and her research team examined 417 Tibetan women, ages 46 to 86, residing at altitudes between 12,000 and 14,000 feet in the Upper Mustang region of Nepal, located on the southern fringe of the Tibetan Plateau.
The team gathered information regarding the women’s reproductive experiences, their physiological readings, DNA samples, and various social influences. Their goal was to explore how traits related to oxygen delivery, particularly under conditions of high-altitude hypoxia (which refers to low oxygen levels in both the air and blood), affect live birth rates—a crucial aspect of evolutionary fitness.
Adapting to thin air
The study revealed that women with the highest number of live births possessed a distinctive combination of blood and heart characteristics that facilitated oxygen delivery. These women maintained hemoglobin levels close to the average of the group but exhibited higher oxygen saturation, resulting in more effective oxygen flow to their cells without increasing blood thickness; thicker blood can put additional pressure on the heart.
“This exemplifies ongoing natural selection,” Beall explained, also serving as the university’s Sarah Idell Pyle Professor of Anthropology. “Tibetan women have evolved to meet oxygen needs without overburdening the heart.”
A glimpse into human evolution
Beall’s diverse research team, which included long-term collaborators Brian Hoit and Kingman Strohl from the Case Western Reserve School of Medicine, conducted fieldwork in 2019. The team collaborated closely with local communities in the Nepal Himalayas, hiring local women as research assistants and consulting with community leaders.
Among the genetic traits studied, one likely dates back to the Denisovans who lived in Siberia around 50,000 years ago; their descendants later settled on the Tibetan Plateau. This trait involves a variant of the EPAS1 gene found exclusively in indigenous populations of the Tibetan Plateau that regulates hemoglobin levels. Additional adaptations, such as enhanced blood flow to the lungs and larger heart ventricles, improved oxygen delivery further. These adaptations contributed to higher reproductive success and provide insight into how humans thrive under consistently low oxygen conditions.
