This article offers a cognitive theory of religious postulations of demonic beings in religious systems. I suggest a significant tension between a biological inheritance of moderate sexual promiscuity and the culturally imposed ideal of exclusive monogamy generates the salience of libidinous supernatural agents to human minds. I review sexual selection theory as applied to humans, the sexual proclivities of demonic cultural constructs, and survey the literature on demonic beings in religious systems. I offer statistical evidence of groupings of demon beliefs (...) around the chief tension points suggested by sexual selection theory. I end with suggestions for further empirical testing of the theory. (shrink)