Exploring Human Adaptation to High Altitudes

Exploring Human Adaptation to High Altitudes

Cynthia Beall’s decades of research in the Andes and Himalayas have shaped our understanding of human biological adaptation to extreme environments.
By Jenna Schnuer

While growing up on what used to be farmland in upstate New York, Cynthia Beall, PhD, never dreamed of trekking the Andes or the Himalayas. She wasn’t one of those kids who disappeared into their minds, imagining far-off adventures while their parents stood five feet away asking them to finish their chores.

Beall’s route into the mountains was both more direct and completely by chance. It was the fall semester of her senior year at the University of Pennsylvania, and she needed to fulfill a general education requirement for her diploma. Beall’s course of choice for that requirement? A class called physiological anthropology. “And wow, I loved it,” she says. “I thought, ‘Well, this brings everything together. It’s people, it’s the environment, it’s biology.’” 

The love stuck. Beall became a biological anthropologist. She has been a professor at Case Western Reserve University in Cleveland since 1976. She is also co-director of the university’s Center for Research on Tibet.

“My field, biological anthropology, is focused on understanding why there’s so much human biological variation. And not only why, but how. The ‘why’ is the big question—are they adapted to the environment—the evolutionary questions. The ‘how’ is the genetics, the physiology, the anatomy, the biochemistry.”

The Importance of Altitude

After earning her undergraduate degree in 1970, Beall went on to get her master’s and PhD at The Pennsylvania State University. The focus of her research came into view during her PhD program. Her adviser was researching how people adapt to high altitude in the Andes. He was studying the Quechua people, who lived in a remote high-altitude village. 

Beall joined a team of other PhD students helping him with his research. “It was fascinating because of what we could see about how their biology in many cases mirrored, or was qualitatively similar, to the biological response you and I would make,” Beall says. “Not in everything, but in a number of traits.”

When, say, lowlanders from the U.S. or Europe go to high altitude, their hemoglobin concentrations will increase and stay high. Oxygen saturation goes down. It’s the same for Andean highlanders. 

But things are different when it comes to breathing. When somebody who lives at low altitude decides to trek up a mountain, their breathing increases. But over time, that ventilatory response becomes blunted. Andean highlanders also have a blunted response. “With the hemoglobin, it does not seem to be a function of how long you’ve been in altitude, but with the breathing it does,” Beall says.

Beall’s early work with her adviser also helped her understand why working at altitude was essential for the kind of research she wanted to do. Altitude remains the same. “At high altitude it’s easy to measure the environmental stress by measuring barometric pressure. Everyone at a given altitude has the same stress,” she says.

That’s unlike, for example, looking at the environmental stress of temperature. “If you and I went to the Sahara, you might have different gear than I do, so we might be exposed to temperature slightly differently. Or maybe I went one year, and you went a different year, and it was hotter one year than another,” she says. “So, for some environmental stresses, it’s harder to measure the stress.” 

One of the other elements that Beall considered when she began her work was evolution, but she says it alone could not explain the variation among people, partly because evolutionary changes occur over long timeframes. Instead, the Andean highlanders displayed signs of developmental adaptation, having grown up in an environment with constant exposure to high-altitude stress. This adaptation led to the development of barrel chests, which accommodate larger lungs.

Heading to the Mountains

Beall’s first visit to the field didn’t quite make it to the heights she would eventually work up to. Instead, she and several other graduate students were on the coast of Peru studying Quechua highlanders who had migrated down to lower elevation. 

She started to learn just enough Spanish to hold rudimentary chats. Beall enjoyed talking to the research participants, collecting biological measurements and household data. She continued her work in the Andes throughout graduate school. After completing the program, one of her colleagues at Case Western Reserve University asked, “Have you ever thought about working in the Himalayas?” Her response? “Only in my dreams.”

At the time, most of the Himalayas were not open to foreigners. But a new colleague had worked in Nepal at high altitude. He wasn’t interested in researching biology, but he had some experience, and he knew how to organize a high-altitude trek. Even more importantly, he had contacts in the area who could help make essential introductions to locals Beall could work with along the way.

In less than a year after defending her dissertation, Beall began organizing her first trip to the Himalayas. It would kick off years of research centering on human adaptations to high-altitude hypoxia, mostly focused on Andean, Tibetan and East African highlanders.

Beall outlined the criteria her research required, and her colleague set off to figure out the perfect location. Before long, he came back with good news: “I found the perfect place. It’s only an eight-day walk.” Beall thought she misheard. “You mean eight hours?” No, eight days. 

Beall had no experience with camping or hiking on the flat farmland where she grew up. While her graduate work in the Andes exposed her to high-altitude research, it didn’t involve trekking or camping. “I was used to being outside,” she says, “but we didn’t do anything like that. It was all new to me.”

Her mom helped outfit her for the trip by buying her a tent. “She bought a really brightly colored one so if anything happened, it would be easy to spot me,” Beall says. “And I headed out.” With her for the trek were an interpreter, a cook and a guide. She had one very simple question: Did Tibetans adapt to high altitude the same way that Andean highlanders did?

She says that first trek into the Himalayas was a very basic pilot study using minimal equipment. It was monsoon season “so it was dark and kind of crappy weather.” She and the interpreter spent time explaining to locals what they were doing and why. The first publication from that study—which she says is the first observation that has carried through to this day—came out in 1981. 

“One nice thing about people who live at high altitudes is they know they’re special,” Beall says. That literal pride of place made it easy for Beall to be honest and tell potential research subjects that she wanted to understand what made them so different from her.

Finding Her Place

That monsoon season trip made Beall question her enthusiasm for trekking through rainstorms, but it didn’t stop her. She returned again and again. Once, while working with a group of Tibetan nomads, she camped midwinter at 17,000 feet on the Tibetan plateau. “I can tell you it’s cold,” she says. “The lowest it got was 29 below—without factoring in the windchill.”

Those trips led to several comparative studies where she looked at Tibetans in the Himalayas and Quechua in the Andes who lived at the same altitude. Her most recent research started in 2012 and continued through last fall “in various forms.”

One project involved five months of trekking to 48 villages. Along the way, Beall learned the importance of involving villagers in the research process and ensuring clear communication to build trust. To address concerns and encourage participation, she and her team held public demonstrations to explain their work and answer questions. “Otherwise, rumors start to fly: ‘Oh, she’s collecting blood and she’s going to sell it,’” Beall says. And when people told her they weren’t comfortable with some form of collection or another, then the researchers just had to make do or find another way. “Any field worker will tell you [that] you have to be flexible,” she says.

She has also learned that it helps to team up with cultural anthropologists who know local dialects and have built up trust from village to village. Then it’s a matter of respectfully asking about collaborating, without jeopardizing what the anthropologist has worked so hard to build.

Beall’s research has gone far beyond lung function into rates of birth and many other areas. She continues to build on the layers she’s learned over 40 years of trekking. And, over time, she has also helped bring people from the Tibet Autonomous Region to the U.S. to learn English or get degrees so they could return home and do their own research. 

As for the future, Beall says her trekking days might be over. Though she retired from teaching a year ago, she has plenty of in-office work organizing data and writing up years of research. Overall, she says organizing the 48-village trek sounds easier. “The trek was very goal oriented,” she says. “This cataloging past work is organizing on a different scale.” 

This article was originally published in the March 2025 issue of The Physiologist Magazine. Copyright © 2025 by the American Physiological Society. Send questions or comments to tphysmag@physiology.org.