A common gender stereotype is that males are more interested than females in sex for purely physical reasons. Sociobiologists claim that this difference is biologically determined. In contrast, many sociologists and anthropologists claim that the difference is cultural. The debate about nature versus nurture regarding sexual interest has been long-standing without resolution. We propose a biosocial model that integrates data about nature and nurture to show (i) how several biological factors tilt males and females in different directions related to sexual interest, and (ii) how numerous social factors influence the way the biological tilts can be redirected in countless different ways as individuals grow up in subsets of their culture and subculture. This interactionist approach does not down-play the importance of either biological or social factors: It avoids nature-nurture debates that pit nature against nurture by showing how biological and social factors act in concert, combining their influences. The resulting work contributes to both the theoretical and practical literature, not only showing how sexology can deal with issues of nature and nurture but also providing information useful to people who are troubled about common gender differences in sexual interest.