“You make me sick”: Moral dyspepsia as a reaction to third-party sibling incest

A pilot study and two main studies lent support to the hypothesis that appraisals of consensual sibling incest as immoral may directly engender the phenomenological state of oral inhibition (OI), comprised of nausea, gagging, and diminished appetite. More specifically, the findings indicate that (a) OI is a central component of a third-party reaction to sibling incest (significantly more so than anger or fear), (b) that it is produced specifically by the morally proscribed aspect of the incestuous relationship (sex between two individuals with common ancestry), and that (c) it is produced so directly rather than as a by-product of a more immediate emotional response (say, intense anger or fear). Furthermore, Study 2 found equal levels of OI for individuals with and without opposite-sex siblings, indicating that third-party aversion to consensual incest is, most likely, a function of the culturally transmitted information regarding the inherent wrongness of such acts.