Three High-Altitude Peoples, Three Adaptations to Thin Air

Hillary Mayell
for National Geographic News
February 25, 2004

Prehistoric and contemporary human populations living at altitudes of at least 8,000 feet (2,500 meters) above sea level may provide unique insights into human evolution, reports an interdisciplinary group of scientists.

Indigenous highlanders living in the Andean Altiplano in South America, in the Tibetan Plateau in Asia, and at the highest elevations of the Ethiopian Highlands in east Africa have evolved three distinctly different biological adaptations for surviving in the oxygen-thin air found at high altitude.

"To have examples of three geographically dispersed populations adapting in different ways to the same stress is very unusual," said Cynthia Beall, a physical anthropologist at Case Western Reserve University in Cleveland, Ohio. "From an evolutionary standpoint the question becomes, Why do these differences exist? We need to figure out when, how, and why that happened."

To begin to answer some of these questions, a multidisciplinary group of scientists, including Beall, met earlier this month at the annual meeting of the American Association for the Advancement of Science in Seattle, Washington.

"High-altitude populations offer a unique natural lab that allows us to follow [many] lines of evidence—archaeological, biological, climatological—to answer intriguing questions about social, cultural, and biological adaptations," said Mark Aldenderfer, an archaeologist at the University of California, Santa Barbara, who organized the AAAS symposium with Beall.

(Aldenderfer and Beall are both past recipients of research grants from the National Geographic Society Committee for Research and Exploration.)

Adapting to High Altitudes

The Andean and Tibetan plateaus rise some 13,000 feet (4 kilometers) above sea level. As prehistoric hunter-gatherers moved into these environments, they encountered desolate landscapes, sparse vegetation, little water, and a cold, arid climate.

In addition, early settlers to the high plateaus likely suffered acute hypoxia, a condition created by a diminished supply of oxygen to body tissues. At high altitudes the air is much thinner than at sea level. As a result, a person inhales fewer oxygen molecules with each breath.

Symptoms of hypoxia, sometimes known as mountain sickness, include headaches, vomiting, sleeplessness, impaired thinking, and an inability to sustain long periods of physical activity. At elevations above 25,000 feet (7,600 meters), hypoxia can kill.

The Andeans adapted to the thin air by developing an ability to carry more oxygen in each red blood cell. That is: They breathe at the same rate as people who live at sea level, but the Andeans have the ability to deliver oxygen throughout their bodies more effectively than people at sea level do.

"Andeans counter having less oxygen in every breath by having higher hemoglobin concentrations in their blood," Beall said. Hemoglobin is the protein in red blood cells that ferries oxygen through the blood system. Having more hemoglobin to carry oxygen through the blood system than people at sea level counterbalances the effects of hypoxia.

Continued on Next Page >>


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