Virginia J. Vitzthum

Department of Anthropology, The Kinsey Institute for Research in Sex, Gender and Reproduction

Indiana University

 

It is widely assumed that, absent pathology and various stressors, natural variation in ovarian steroid concentrations within and between human populations is positively associated with variation in individual lifetime reproductive success, but this assumption has yet to be empirically evaluated. Here we present new findings that directly test the hypothesis that inter-individual variation in progesterone concentrations during the most fecund portion of the lifespan predicts variation in female total fertility at the completion of reproduction. We recently collected updated reproductive histories and hormonal data from participants in Project REPA, a study of Bolivian agropastoralists begun 20 years ago. We have previously demonstrated that conception and gestation are not negatively affected by these Bolivians' relatively low progesterone concentrations. These findings are consistent with the argument thatthe most salient signal for modulating an individual's investment in a given reproductive opportunity is a temporal change in ovarian steroid concentrations rather than the absolute concentration per se (i.e., transient state rather than typical trait is the principal mediator of reproductive effort). Here we extend this prior work by evaluating the extent to which ovarian steroid concentrations predict total lifetime conceptions, pregnancy loss, and fertility. [Funded by NSF (9506107, 1142201) and OVPR, Indiana University, Bloomington]