Deformed nasal septa and relaxed selection

Abstract

Demographic studies undertaken in several Andean countries have found that women residing at high altitudes have significantly fewer live births than do their low altitude counterparts. This reduction has been explained as being due to various factors: the debilitating effects of hypoxia upon the reproductive system; the effects of sociocultural factors which vary with altitude and which affect reproductive behavior; and errors in data collection. In order to examine the validity of some of these hypotheses, the fertility of a group of 906 Bolivian women residing at low, medium, and high altitudes was examined. The women were selected from the lower socioeconomic strata and reported never having used any method of contraception. A detailed analysis of the fertility of these women showed no significant altitude‐related differences in the number of live births. However, as a result of significantly higher childhood mortality rates at altitude, there was a significant reduction in numbers of living children. The results of this study suggest that the collection and analysis of census data that ignores socioeconomic differences within a population or differences among census units in neonatal or early childhood mortality may bias or complicate the study of the impact of altitude on human fertility. Although the present research does not prove that hypoxic stress does not affect the reproductive system, the results suggest that if altitude does reduce fecundity, the reduction is not great and is likely to be shown only through studies of reproductive physiology.