ABSTRACT
One of Westermarck's most debated contributions was his hypothesis that natural selection has shaped human sexuality to not encompass sexual attraction to individuals with whom one coresided in early youth. The debate surrounding Westermarck's explanation of incest avoidance has often been imprecise, and his explanation has often been treated as an uncomplicated and simple hypothesis. This chapter introduces Westermarck's hypothesis regarding the natural origins of the human inbreeding avoidance and the incest taboo. It itemises the hypothesis, arguing that, rather than being one simple hypothesis, it contains at least four independent assumptions. The assumptions are: the assumption of ultimate evolutionary causation; the assumption of childhood coresidence as the proximate individual-level activation; the assumption of imperfect functioning; and the assumption of a social extension of the individual aversion. The chapter discusses each of the assumptions embedded in Westermarck's reasoning in the light of philosophical arguments and empirical data that have been presented as supporting or falsifying Westermarck's position.
