This chapter provides the results of an empirical investigation of a question concerning motivation—do men maximize children, or the amount of wealth they can give their children? It describes the method here which can be used to determine what is being maximized in any behavioral domain. The chapter focuses on the marital decisions of men in a rural Kenyan Kipsigis population. Many Kipsigis men marry more than one wife, such that there is high variance in men's reproductive success. Women almost invariably marry soon after puberty, but men's age at marriage is much more variable, with the median ranging from 21 to 25 years between the 1950s and the 1980s. Reproductive costs associated with polygynous marriage for women are not high, suggesting that poor men are generally unable to either coerce or attract additional wives.