In this paper I use measures of childhood growth to assess from both an evolutionary theoretical and an applied public health perspective the impact of polygyny on maternal-child welfare among the Datoga pastoralists of Tanzania. I report that the growth and body composition of children varies in such a way as to suggest that polygyny is not generally beneficial to women in terms of offspring quality. Cross-sectional analysis of covariance by maternal marriage status revealed that children of first and second (...) wives in polygynous marriages grow relatively poorly, that this is correlated with maternal physical status, and that the pattern is not modified by household wealth. I discuss how the dynamics of sexual conflicts operating during the formation and maintenance of marriages may be important factors in the etiology of poor child growth in this population, leading to complex patterns of variation in anthropometric indicators of both women and children. The theoretical conclusion is that improved evolutionary models of polygyny should be designed to examine the potential for adaptive tradeoffs between the currencies of offspring quality and quantity for all types of parents in a polygynous population. The practical conclusion is that a better understanding of the relationships between marriage practices and health outcomes would assist in the development of culturally appropriate health and nutrition interventions. (shrink)