Data from: Ethnically Tibetan women in Nepal with low hemoglobin concentration have better reproductive outcomes

Abstract Background and objectives: Tibetans have distinctively low
hemoglobin concentrations at high altitudes compared with visitors and
Andean highlanders. This study hypothesized that natural selection favors
an unelevated hemoglobin concentration among Tibetans. It considered
nonheritable sociocultural factors affecting reproductive success and
tested the hypotheses that a higher percent of oxygen saturation of
hemoglobin (indicating less stress) or lower hemoglobin concentration
(indicating dampened response) associated with higher lifetime
reproductive success. Methodology: We sampled 1006 post-reproductive
ethnically Tibetan women residing at 3000–4100 m in Nepal. We collected
reproductive histories by interviews in native dialects and noninvasive
physiological measurements. Regression analyses selected influential
covariates of measures of reproductive success: the numbers of
pregnancies, live births and children surviving to age 15. Results: Taking
factors such as marriage status, age of first birth and access to health
care into account, we found a higher percent of oxygen saturation
associated weakly and an unelevated hemoglobin concentration associated
strongly with better reproductive success. Women who lost all their
pregnancies or all their live births had hemoglobin concentrations
significantly higher than the sample mean. Elevated hemoglobin
concentration associated with a lower probability a pregnancy progressed
to a live birth. Conclusions and implications: These findings are
consistent with the hypothesis that unelevated hemoglobin concentration is
an adaptation shaped by natural selection resulting in the relatively low
hemoglobin concentration of Tibetans compared with visitors and Andean
highlanders.