ABSTRACT
Humans rely on moral reasoning to determine whether a target belongs to the category human or not. We propose an evolutionary theory of the boundary conditions for moral reasoning engagement, particularly as it relates to ingroups and outgroups. Morality co-opted disgust as an emotional response to protect the ingroup from violation. We argue that moral reasoning—and subsequent attribution of humanity—is gated by the same principle that regulates disgust and more general emotional responding: contaminant proximity. Proximity—both physical and psychological—of a violator to a harm determines whether moral reasoning gets engaged or not. This engages avoidance action-tendencies that short-circuit moral reasoning, resulting in moral disengagement. Finally, there exist prepared stimuli that trigger moral intuition without moral reasoning. We describe gates that determine whether moral reasoning is facilitated or inhibited, explaining moral decisions, and moral behaviour toward ingroups and outgroups driven by whether they are considered fully human.
