(Final version accepted 8 November 2010)

A review of cross-species and cross-cultural research suggests that, throughout most of human behavioral evolution, children may have been enlightened as to the facts of life by observing parental intercourse and then imitating it in sexual rehearsal play in the context of a continuously rising curve of sexual desire and sexual knowledge throughout childhood. Concealment of the primal scene and prohibition of cross-generational, bisexual, and ‘polymorphously perverse’ childhood sex play may be of relatively recent origin in human cultural evolution, buttressed by the instillation of culturally acquired sexual disgust in sexually conservative cultures. Looking at the primal scene in cross-species and cross-cultural perspectives utilizing the adaptationist framework of contemporary evolutionary biology can challenge normative assumptions that may still be embedded in psychoanalytic theories of species-wide psychosexual development.