AbstractThe reproductive self-interest model of morality (RSIMM) is a framework for understanding moral judgments associated with sexual behavior. This model posits that individual differences in sexual strategies, mediated by one's religiosity and political orientation, casually influence people's moral judgments toward social hot-button issues. Previous work on the RSIMM has explained individual differences in attitudes toward abortion, prostitution, and contraception. Individuals more interested in long-term mating judged these behaviors as morally wrong. In this preregistered study, we proposed the RSIMM would account for individual differences in rape myth acceptance (RMA). RMA is the phenomenon of endorsing beliefs or stereotypes about rape that diminish the severity of assaults or shift blame from perpetrators to victims. We examined the relationship between political orientation, attitudes toward third-party casual sex, and RMA in a convenience sample of 308 participants (137 women). We predicted that more negative attitudes toward third parties' casual sex would correlate with increased RMA. Our hypothesis was supported for men but not women: Men who condemned others' casual sex, had more unrestricted attitudes about their own casual sex, and desired more casual sex were statistically more likely to accept more rape myths. In the discussion, we speculate that sex differences in the relationship between attitudes towards casual sex and RMA may be due to the costs of rape incurred by women but not men.