Religion has often been conceptualized as a collection of beliefs, practices, and proscriptions that lift people’s thoughts and behaviors out of the metaphorical gutter of sex and selfishness toward lives full of meaning, contemplation, and community service. But religious beliefs and behaviors may serve selfish, sexual motivations in ways that are not always obvious or consciously intended. We review two lines of research illustrating nonobvious links between the mundane and the religious. First, contrary to long-held assumptions that religious upbringing causes sexually restrictive attitudes and behaviors, several large data sets now suggest a reverse causal arrow—people’s preferred mating strategies determining their attraction toward, or repulsion from, religion. Second, other recent findings suggest that distrust of nonreligious individuals is almost completely erased by knowledge that they are following a restricted monogamous lifestyle. Thus, reproductive strategies often underlie apparently sacred concerns. We close with a consideration of ways in which reproductive interests might underlie a broad range of benefits associated with religious affiliation.