Complementarity theory: why human social capacities evolved to require cultural complements.

This article introduces complementarity theory, which explains the psychology of cultural diversity as a product of evolved social proclivities that enable-and require-people to coordinate action in culture-specific ways. The theory presents evolutionary processes and psychological mechanisms that may account for the cultural variability of social coordination devices such as language, relational models, rituals, moral interpretations of misfortune, taboos, religion, marriage, and descent systems. Human fitness and well-being depend on social coordination characterized by complementarity among the participants' actions. This complementarity is based primarily on coordination devices derived from the conjunction of cultural paradigms and specific, highly structured, evolved proclivities. The proclivities have no adaptive value without the paradigms, and the paradigms have no meaning without the proclivities. They are coadapted to function together. Operating in conjunction with each other, proclivities and paradigms jointly define the generative structures for meaningful coordination of social interaction in each particular culture.