A behavioural immune system perspective on disgust and social prejudice

Infectious disease threatens humans across cultures and time periods. The mental mechanisms that have evolved to navigate this threat can have non-intuitive consequences for phenomena such as political ideology and social prejudice. In this Review, we describe these mental mechanisms (together called the behavioural immune system), review the evidence that they contribute to prejudice and critically evaluate evidence for two proposed underlying principles: that the behavioural immune system functions according to a ‘better safe than sorry’ bias (the smoke detector principle) and generates prejudice towards people with atypical features. We find that evidence supports both features. However, most evidence for the smoke detector principle remains indirect, and only specific types of atypicality seem to evoke prejudice. These considerations lead to two priorities for future research. First, research should apply signal detection methods to more directly test whether the behavioural immune system leads to prejudice because of a bias towards false alarms. Second, research should focus on testing the extent to which explanations based on low interpersonal value can account for relations between pathogen-avoidance motivations and prejudice towards groups and individuals associated with norm violations. The behavioural immune system consists of psychological mechanisms that evolved to prevent pathogens from entering the body (such as avoiding stimuli that elicit disgust). In this Review, van Leeuwen et al. consider how pathogen avoidance gives rise to prejudice and evaluate the empirical support for principles hypothesized to underlie this phenomenon.