Cynthia M. Beall

Anthropology Department

Case Western Reserve University

 

Reproduction and survival of offspring are central to evolution and adaptation. Understanding how these events play out in real populations is important for understanding the pace at which evolution and adaptation may occur. High-altitude populations are informative in this context because they have adapted to a severe environmental stress. However, in addition to genetic and phenotypic maternal characteristics, non-biological factors can exaggerate or dampen individual variation in reproductive success. This study tested the hypothesis that environmental, sociocultural, and economic determinants along with biological adaptations predict the number of pregnancies, livebirths and children surviving to 15 years of age in a sample of 1,006 Tibetan women who were native residents at altitudes from 3,000 -4,100m in two districts in Nepal. Richer women and women who had used contraception had nearly two more pregnancies and livebirths. In contrast, hemoglobin, percent of oxygen saturation of hemoglobin, and pulse made very small contributions that trended toward statistical significance. Altitude was not a significant predictor. We conclude that environmental, cultural and economic factors introduced heterogeneity into women’s lives with consequences for widely-used measures of reproductive success. Such effects were orders of magnitude larger than those of biological factors.