In the rarefied atmosphere of Nepal’s highlands, researchers are observing the evolution of humans in real-time as they adjust to one of the planet’s most extreme environments. At elevations above 3,500 meters (approximately 11,500 feet), oxygen levels plummet. Most individuals who climb to these heights without proper acclimatization face the threat of altitude sickness, a situation that arises when the body is unable to obtain sufficient oxygen. However, for many generations, populations on the Tibetan Plateau have not just survived but flourished under these circumstances.
A research project spearheaded by anthropologist Cynthia Beall from Case Western Reserve University uncovers how individuals in this area have physically adapted to confront the challenges of low-oxygen living. The team examined 417 women, all long-time inhabitants of high-altitude regions in Nepal. By assessing various metrics from hemoglobin levels to heart size, they aimed to identify which characteristics enabled some women to have more offspring than others, a critical measure of evolutionary success.
The women who experienced the greatest number of live births did not possess the highest or lowest hemoglobin levels. Instead, their measurements fell within the average range. What truly distinguished them, however, was their oxygen saturation. Their bloodstream was better at transporting oxygen without becoming viscous, a balance that alleviates pressure on the heart. These women also exhibited wider heart ventricles and enhanced blood flow to the lungs. Collectively, these characteristics result in more oxygen being delivered to tissues, which is essential in an environment where the air contains less of it.
This phenomenon extends beyond mere survival. It pertains to reproduction and the transmission of traits that facilitate life at high altitudes. While sociocultural aspects also influence family size, the physiological benefits were unmistakable. These attributes are not coincidental; they represent natural selection at work. Human evolution is far from complete. It is occurring right now, within the lungs, blood, and hearts of individuals inhabiting the Himalayas. And as we investigate these transformations, we hope to gain insights not only into our past but also into our future.
