Through the application of life course theory to the study of sexual orientation, this paper specifies a new paradigm for research on human sexual orientation that seeks to reconcile divisions among biological, social science, and humanistic paradigms. Recognizing the historical, social, and cultural relativity of human development, this paradigm argues for a moderate stance between essentialism and constructionism, identifying (a) the history of sexual orientation as an identity category emerging from the medical model of homosexuality in the late 1800s; (b) the presence of same-sex desire across species, history, and cultures, revealing its normality; (c) an underlying affective motivational force which organizes sexual desire within individuals, and (d) the assumption of a sexual identity in response to the identity and behavioral possibilities of a culture. This framework considers the biology of sexual desire while simultaneously acknowledging the socially constructed nature of identity and the historical foundations of sexual orientation as a meaningful index of human identity.