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Archive - Dec 8, 2012

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Convergent Evolution Observed in Human Adaptation to High Altitude

Highlanders in Tibet and Ethiopia share a biological adaptation that enables them to thrive in the low oxygen of high altitudes, but the ability to pass on the trait appears to be linked to different genes in the two groups, research from a Case Western Reserve University scientist and colleagues shows. The adaptation is the ability to maintain a relatively low (for high altitudes) level of hemoglobin, the oxygen-carrying protein in red blood cells. Members of ethnic populations - such as most Americans - who historically live at low altitudes naturally respond to the thin air by increasing hemoglobin levels. The response can help draw oxygen into the body, but increases blood viscosity and the risks for thrombosis, stroke, and difficulties with pregnancies. By revealing how populations can live in severe environments, the research may provide insight for managing high-altitude sickness and for treating low blood-oxygen conditions such as asthma, sleep apnea, and heart problems among all people. How long such physiological and genetic changes take remains a question. The researchers found the adaptation in an ethnic group that has lived high in mountains of Ethiopia for at least 5,000 years, but not among a related group that has lived high in the mountains for 500 years. The findings were reported on December 6, 2012 in the open-access online journal PLoS Genetics. In their first comparison, the researchers found that the genes responsible for hemoglobin levels in Tibetans don't influence an ethnic group called the Amhara. The Amhara have lived more than a mile high in the Semien Mountains of northern Ethiopia for 5,000 to 70,000 years. A different variant on the Amhara genome, far away from the location of the Tibetan variant, is significantly associated with their low hemoglobin levels.