HEMOGLOBIN CONCENTRATION OF HIGH-ALTITUDE TIBETANS AND BOLIVIAN AYMARA

Elevated hemoglobin concentrations have been reported for high-altitud e sojourners and Andean high-altitude natives since early in the 20th century. Thus, reports that have appeared since the 1970s describing r elatively low hemoglobin concentration among Tibetan high-altitude nat ives were unexpected. These suggested a hypothesis of population diffe rences in hematological response to high-altitude hypoxia. A case of q uantitatively different responses to one environmental stress would of fer an opportunity to study the broad evolutionary question of the ori gin of adaptations. However, many factors may confound population comp arisons. The present study was designed to test the null hypothesis of no difference in mean hemoglobin concentration of Tibetan and Aymara native residents at 3,800-4,065 meters by using healthy samples that w ere screened for iron deficiency, abnormal hemoglobins, and thalassemi as, recruited and assessed using the same techniques. The hypothesis w as rejected, because Tibetan males had a significantly lower mean hemo globin concentration of 15.6 gm/dl compared with 19.2 gm/dl for Aymara males, and Tibetan females had a mean hemoglobin concentration of 14. 2 gm/dl compared with 17.8 gm/dl for Aymara females. The Tibetan hemog lobin distribution closely resembled that from a comparable, sea-level sample from the United States, whereas the Aymara distribution was sh ifted toward 3-4 gm/dl higher values. Genetic factors accounted for a very high proportion of the phenotypic variance in hemoglobin concentr ation in both samples (0.86 in the Tibetan sample and 0.87 in the Ayma ra sample). The presence of significant genetic variance means that th ere is the potential for natural selection and genetic adaptation of h emoglobin concentration in Tibetan and Aymara high-altitude population s. (C) 1998 Wiley-Liss, Inc.