Disgust elicited by third-party incest: the roles of biological relatedness, co-residence, and family relationship

At an ultimate level of explanation, the causes of incest aversion have been linked to the reproductive costs of inbreeding, whereas at a proximate level of explanation, experienced environmental cues relating to the successful recognition of kin have been shown to moderate both the likelihood of engaging in incest and the aversion to descriptions of third-party incest. However, little is known concerning how incest aversion is moderated by evolutionarily relevant factors presented in such descriptions. As disgust has been suggested to down-regulate incestuous sexual interest, we investigated to what extent the gender, biological relatedness, co-residence, and family-relationship type of actors described in incest scenarios moderate the elicited disgust of men and women reading those descriptions. Analyzing responses from 434 participants, we found that women are more disgusted by incest than men, that descriptions of biological incest elicited more disgust than sociolegal incest, that descriptions of incest between family members having co-resided elicited more disgust than incest between family members growing up apart, and that descriptions of incest between a parent and a child elicited more disgust than incest between siblings. Our conclusion is that variations in the degree of disgust elicited by descriptions of third-party incest are consistent with evolutionary hypotheses concerning inbreeding avoidance.