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Humans are still evolving, as shown by a community in the Tibetan Plateau that has developed unique adaptations helping them thrive at high altitudes with thin air and lower oxygen levels for more than 10,000 years.
Over thousands of years, humans have evolved various adaptations to survive in our planet's environments, such as skin pigmentation, which helps protect against ultraviolet (UV) radiation.
Adaptations are still being observed, particularly in the region of the Tibetan Plateau, aptly nicknamed the “Roof of the World”. It is a vast landscape in Central Asia with a cold and dry climate and thin air because of its high elevation 4,500 meters above sea level.
Lower atmospheric pressure, which occurs at higher altitudes, can result in less oxygen entering the lungs, blood and our body’s tissues with each breath. This is why mountain climbers may experience hypoxia which is often referred to as altitude sickness.
Tibetan Plateauen.wikipedia.org
Despite thin air, Tibetans’ bodies adapt to deliver oxygen efficiently. Anthropologist Cynthia Beall of Case Western Reserve University in the US studies the human response to hypoxic living conditions. Along with her team, she discussed some of the specific adaptions in Tibetan communities in research published in October 2024.
The team looked at evolutionary fitness, which refers to an organism’s ability to survive and reproduce in a given environment to pass on its genes to the next generation. These survival traits are likely to be identified in women who are able to survive the stresses of pregnancy and childbirth, and these children will be likely have the traits to survive and pass on these traits to the next generation.
The researchers studied 417 women aged between 46 and 86 who lived all their lives in Nepal above altitudes of 3,500 metres. Beall and the team recorded the number of live births ranging between 0 and 14 per woman, with an average of 5.2.
The researchers measured haemoglobin levels, the protein in red blood cells that carries oxygen to body tissues, and how much oxygen the haemoglobin was actually transporting. Surprisingly, the women with the highest rate of live births had average levels of haemoglobin, however the oxygen saturation of the protein was high.
This suggests they have evolved to maximise oxygen delivery without thickening the blood, which would place more stress on the heart as it would have to pump blood with increased viscosity. The women with the highest reproductive success rate also had wider than average left ventricles in their hearts, and this chamber is responsible for pumping oxygenated around the body.
"Previously we knew that lower haemoglobin was beneficial, now we understand that an intermediate value has the highest benefit. We knew that higher oxygen saturation of haemoglobin was beneficial, now we understand that the higher the saturation the more beneficial. The number of live births quantifies the benefits," Beall told ScienceAlert.
"It was unexpected to find that women can have many live births with low values of some oxygen transport traits if they have favourable values of other oxygen transport traits."
"This is a case of ongoing natural selection," Beall said, via The Daily. “Tibetan women have evolved in a way that balances the body’s oxygen needs without overworking the heart.”
Once again, human evolution continues to amaze us at every altitude!
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