New discoveries by Case Western Reserve University anthropologist Cynthia Beall continue to unravel the mystery of how humans have adapted to high altitude living.

In her hematological study of villagers in the Semien Mountains of Ethiopia, she found that this population differs biologically from people on the Tibetan and Andean plateaus, but in a couple of key aspects does not differ from people at sea level.

Beall, CWRU's Sarah Idell Pyle Professor of Anthropology, reported the research findings in the article, "An Ethiopian Pattern of Human Adaptation to High-Altitude Hypoxia" in the Proceedings of the National Academy of Sciences (PNAS).

Twenty years ago, Beall's research on Tibetans began to overturn the long-held model of the "Andean man" with the large barrel chest and high concentrations of hemoglobin, the oxygen-carrying molecule in the blood. Despite high hemoglobin concentrations, the Andean highlanders have low oxygen saturations of hemoglobin relative to sea level.

Beall discovered Tibetans had normal sea-level hemoglobin with low oxygen saturations but there is a variation among Tibetans with some having a genetic allele for higher oxygen saturation of hemoglobin.

Now a third way to survive highland living was found among a sample of Ethiopian highlanders, who have normal sea-level hemoglobin and normal sea-level oxygen saturations-a distinct combination of traits, according to Beall.

She made the discovery from data collected in a field study of 313 native residents at 3,530 meters (11,650 feet of altitutde) between the ages of 14-86 years old from the Ambaras Region of the Semien Mountains National Park, Ethiopia. The Ambaras people are farmers of barley and herders of cattle, goats and sheep. They live in small villages scattered across the plateau in northeastern Ethiopia.

With the assistance of Amha Gebremedhin, from the department of internal medicine at Addis Ababa University, and local peasant associations, Beall contacted the villagers and was able to gather blood samples for analyses of their hemoglobin content as well as erythropoietin, a hormone that stimulates the production of stem cells in the bone morrow to produce blood cells and also an indicator of hemoglobin levels.

The Ambaras people live in small villages scattered across the plateau in the northeast part of Ethiopia. Because the Amabaras have experienced famines and other hardships, Beall ruled out anemia, infections and inflammations that might also skew the findings.

Healthy sea-level dwellers have saturations of oxygen in their bloods that vary from 92-100 percent. In the Amabaras sample, the oxygen saturation averaged 95 percent, which surprised Beall, because the oxygen saturation in the Andean and Tibetan highlanders at similar altitudes was in the mid to high 80s.

"This raised the question of how did they achieve this? We looked to see if they had normal hemoglobin or a special form of hemoglobin, but they did not," Beall said. "It seems that people living at high altitude in Ethiopia have very little hypoxic stress. These findings suggest there are three patterns of adaptation to high-altitude hypoxia among indigenous populations."

Learning why will require two lines of future investigation, according to Beall. One is looking at the biological mechanisms and underlying genetics that allow for successful high-altitude living. The other line is investigating the evolutionary process that produced these adaptation patterns.

In addition to Gebremedhin, other researchers involved in the project were Michael Decker from the department of neurosciences at Emory University and a CWRU undergraduate and graduate school alumnus; Gary M. Brittenham, department of pediatrics, College of Physicians and Surgeons at Columbia University; Irving Kushner, department of medicine at CWRU's Metrohealth Campus; and Kingman Strohl from the department of medicine at CWRU.