Morality is relative: Anger, disgust, and aggression as contingent responses to sibling versus acquaintance harm.

Angry reactions to moral violations should be heightened when wrongs befall oneself in comparison with when wrongs befall acquaintances, as prior research by Molho, Tybur, Güler, Balliet, and Hofmann (2017) demonstrates, because aggressive confrontation is inherently risky and therefore only incentivized by natural selection to curtail significant fitness costs. Here, in 3 preregistered studies, we extend this sociofunctional perspective to cases of wrongs inflicted on siblings. We observed equivalently heightened anger in response to transgressions against either oneself or one's sibling relative to transgressions against acquaintances across studies, whereas transgressions against acquaintances evoked greater disgust and/or fear (both associated with social avoidance) in 2 of the 3 studies. Studies 2 and 3, which incorporated measures of tendencies to confront the transgressor, confirmed that the elevated anger elicited by self or sibling harm partially mediated heightened inclinations toward direct aggression. Finally, in Study 3 we compared tendencies to experience anger and to directly aggress on behalf of siblings and close friends. Despite reporting greater affiliative closeness for friends than for siblings, harm to friends failed to evoke heightened anger relative to acquaintance harm, and participants were inclined to directly aggress against those who had harmed their sibling to a significantly greater extent than when the harm befell their friend. These overall results broadly replicate Molho et al.'s (2017) findings and theoretically extend the sociofunctionalist account of moral emotions to kinship. (PsycInfo Database Record (c) 2021 APA, all rights reserved).