Many people assume that human evolution is something that happened in the distant past, shaping early Homo sapiens before we spread across the planet.
But in reality, evolution never stops. Our bodies are constantly adapting to our environments, and nowhere is this more evident than on the Tibetan Plateau.
At an altitude of over 3,500 meters (11,480 feet), oxygen levels are much lower than at sea level. For most people, this would lead to hypoxia, a condition where the body doesn’t get enough oxygen.
This can cause dizziness, shortness of breath, and even life-threatening complications. Mountain climbers often struggle with these symptoms, yet the communities that have lived on the Tibetan Plateau for over 10,000 years thrive in this environment.
How? Their bodies have evolved remarkable adaptations that allow them to extract and use oxygen far more efficiently than people living at lower altitudes.
And thanks to new research, scientists are beginning to understand exactly how this natural selection process works.
The Science of Survival: A Close Look at Tibetan Adaptations
Anthropologist Cynthia Beall from Case Western Reserve University has spent years studying how the human body responds to living in high-altitude, low-oxygen conditions.
In a study published in October 2024, she and her team revealed specific genetic and physiological traits that help Tibetans survive—and even thrive—where most others would struggle.
One key finding? Women who are best adapted to high altitudes tend to have higher reproductive success.
This means they give birth to more live babies, who then inherit these beneficial traits, ensuring that future generations continue to carry the adaptations forward.
To investigate these adaptations, Beall’s team studied 417 Nepalese women between the ages of 46 and 86 who had lived their entire lives at high altitudes. They measured several physiological traits, including:
- Hemoglobin levels – the protein in red blood cells responsible for carrying oxygen.
- Oxygen saturation – how much oxygen is actually being transported by the blood.
- Blood flow into the lungs – a crucial factor in how well oxygen is absorbed.
- Heart structure – specifically, the size of the left ventricle, which pumps oxygen-rich blood throughout the body.
The Best Adaptation is Balance
Most people assume that in low-oxygen environments, having higher hemoglobin levels would be the best adaptation, since hemoglobin is responsible for transporting oxygen in the blood.
However, Beall’s research uncovered something unexpected.
Women with neither too much nor too little hemoglobin had the highest reproductive success.
Instead, those with the highest oxygen saturation—meaning their blood was exceptionally efficient at carrying oxygen—were more likely to have more children.
Why does this matter? Because too much hemoglobin makes blood thicker and harder to pump, putting extra strain on the heart.
The best-adapted women had just the right balance: enough hemoglobin to transport oxygen effectively, but not so much that it made their blood too viscous.
How the Heart Plays a Role in Evolution
Another crucial adaptation Beall’s team discovered was related to the heart. Women with the highest number of live births tended to have wider-than-average left ventricles, allowing their hearts to pump oxygen-rich blood more efficiently.
This means their bodies could compensate for lower oxygen availability without overworking the heart.
In addition, these women showed higher blood flow to the lungs, which helps absorb as much oxygen as possible from each breath.
These combined traits ensure that their tissues and organs receive an adequate oxygen supply, even in a thin-atmosphere environment where most people would struggle.
The Role of Reproductive Success
Evolution works through natural selection, favoring traits that improve survival and reproductive success.
In this case, the women who had the most children were those with physiological traits best suited for high-altitude living.
This is similar to how people in malaria-prone regions have a higher prevalence of the sickle cell gene—because it provides resistance to malaria, even though it can cause sickle cell disease in some cases. In the Tibetan Plateau, the traits that maximize oxygen efficiency are being passed down to each new generation, gradually refining the population’s ability to survive in extreme environments.
The Role of Culture in Evolution
Interestingly, the study also found that cultural factors play a role. Women who started having children at a younger age and had longer marriages were naturally more likely to have more children.
While this factor alone doesn’t explain the adaptations, it suggests that both biological and social elements influence reproductive success.
Even when accounting for these cultural influences, the study confirmed that physical traits remained the key factor in determining which women had the most children.
The most successful mothers were those whose bodies could best manage oxygen delivery in a low-oxygen environment.
What This Means for Our Understanding of Evolution
Beall’s findings provide a rare opportunity to observe human evolution happening in real time.
Instead of looking at fossils or ancient DNA, scientists can study living populations to see how natural selection continues to shape human physiology today.
“This is a case of ongoing natural selection,” Beall explains. “Understanding how populations like these adapt gives us a better grasp of the processes of human evolution.”
The study sheds light on how humans adapt to extreme environments and provides insights that could even have medical applications.
Understanding how Tibetans efficiently use oxygen might one day help doctors develop treatments for conditions like chronic hypoxia, which affects patients with lung diseases or heart failure.
Evolution is Far from Over
The idea that humans have “finished” evolving is a myth. The Tibetan Plateau is just one example of how human biology continues to change in response to environmental challenges.
As scientists continue to explore high-altitude adaptations, we may discover even more fascinating insights into how our species is still evolving. And who knows?
Perhaps one day, these studies will help unlock secrets that benefit all of humanity, from medical advancements to better understanding our evolutionary journey.
References
Beall, Cynthia. “High-Altitude Adaptation and Natural Selection in Tibetan Populations.” Proceedings of the National Academy of Sciences, October 2024.
Craig, Sienna R., et al. “Noninvasive Measurement of Hemoglobin Concentration and Oxygen Saturation in High-Altitude Populations.” Journal of Human Biology, 2024.
