A new study published in the Proceedings of the National Academy of Sciences reveals a unique physiological adaptation in Tibetan women that contributes to their high reproductive success in the low-oxygen environment of the Tibetan Plateau.
Researchers led by anthropologist Cynthia Beall from Case Western Reserve University studied 417 Tibetan women aged 46 to 86 who had lived their entire lives at an altitude of around 3,500 meters above sea level in Nepal. They found that women with the highest number of live births had an average level of hemoglobin, a protein in red blood cells that carries oxygen, but a higher oxygen saturation in their hemoglobin. This suggests that their bodies have adapted to transport oxygen more efficiently without thickening the blood, which could strain the heart.
The study also found that these women had a higher blood flow to their lungs and a wider left ventricle, the main pumping chamber of the heart. These characteristics further enhance oxygen transport throughout the body, allowing them to thrive in the low-oxygen environment.
While cultural factors, such as starting childbirth at a younger age and longer marriages, also played a role in reproductive success, the study emphasizes the importance of physiological adaptation in this context. The findings demonstrate that natural selection continues to shape human evolution, favoring individuals with traits that best suit their environment.
This study provides further evidence that humans are still evolving in response to the challenges they face, offering valuable insights into the ongoing process of human evolution.