Reproductive Decision-Making in Transitional Contexts

Over the past two hundred years, most societies around the world have experienced fertility transitions, defined as a dramatic decline in reproductive rates through time. The conscious decision to reduce fertility to very low levels appears maladaptive and poses a theoretical challenge to human behavioral ecologists who expect humans to maximize long term fitness. I develop a theoretical model to explain currently low fertility rates that incorporates both cultural and economic hypotheses of fertility decline and test these using data from San Borja, Bolivia, a society currently undergoing a fertility transition. Results show that both economic and cultural information are important determinants of reproductive decisions. Kin are also an important influence on reproductive decision-making, possibly providing help to a reproducing couple or hindering reproduction by engaging in resource competition. I test these hypotheses using data from Thailand and Indonesia and show that couples who receive help from kin are more likely to reproduce in the future, providing evidence for the cooperative breeding hypothesis. Finally, I present some preliminary results from my recent field season in Huatasani, Peru exploring men’s reproductive decision making and discuss theoretical models of sexual conflicts over family size.