A study of an isolated population of Ethiopians has thrown a curve ball to researchers studying how groups adapt to life at high altitude. The Ethiopians' biological response to oxygen-poor air is unlike that seen previously in Andean and Tibetan populations. The various strategies could eventually help explain illnesses such as heart and lung diseases that afflict people at all altitudes.
More than 20 years ago, scientists discovered that people living high in the Andes have more red blood cells and more oxygen-carrying hemoglobin than those living at sea level. Tibetans are different. Living among the peaks of the Himalayas, a Tibetan has about the same amount of hemoglobin as someone living at sea level. Somehow, they make due with far less oxygen in their blood. Curious to see if a group of scarcely studied Ethiopians could shed further light on high-altitude adaptations, Cynthia Beall, a physical anthropologist at Case Western Reserve University in Cleveland, Ohio, began to study natives of the Semien Mountains National Park.
In 1995 and 1996, Beall's team took blood samples from 313 volunteers between the ages of 14 and 86 and living at an altitude of more than 3500 meters. They found that the Ethiopian levels of hemoglobin were very near those of sea level residents, similar to Tibetans. Unlike the Tibetans, however, the Ethiopians' blood held far more oxygen, at concentrations similar to Andean and sea level populations. The Ethiopians must have some yet-unknown way to grab more oxygen from the air without resorting to making red blood cells and hemoglobin, the researchers conclude in the December 2 issue of the Proceedings of the National Academy of Sciences.
"It's a very significant study," says biological anthropologist Tom Brutsaert of the University at Albany, State University of New York. The next step, Brutsaert and Beall agree, is to figure out how the people are pulling in more oxygen. Since many types of heart and lung disease are characterized by low oxygen saturation in the blood, Beall says, understanding adaptations and the genes behind them could shed light on why people with the same disease develop different symptoms.