Advocates of sexual selection theory have argued that various male traits, such as male co-operative behavior towards females, can evolve through female preference for mating with those males who possess that trait. This paper reports on the results of a simulation performed to test the hypothesis that female preference for mating with co-operative males can lead to an increase in the proportions of males in a population who co-operate with females. We simply model the sex differences using a single variable measuring the cost of reproduction. Our results show that even in such a simple environment there are a large number of interacting variables, which complicate the relationship between the sexual selection of co-operative males by females and the proportion of males actually co-operating with females. In fact, in most situations we modeled, sexual selection of co-operative males by females ended up causing the proportion of females that co-operate with males to increase while the p...