Prosocial aggression tracks genetic relatedness distinctly from emotional closeness.

Altruistic behavior is understood to largely stem from adaptations for kin altruism, contingent on degree of relatedness, and/or reciprocal altruism, contingent on degree of benefits conferred in exchange for help. Because kin qualify for both kin reciprocal altruism, they should receive greater support than friends, as has been demonstrated in prior research. Here, we tested this prediction with regard to willingness to punish on another's behalf, comparing inclinations to aggress against transgressors when the victim was framed as an acquaintance, close friend, cousin, sibling, or oneself. Participants endorsed comparably greater direct aggression on behalf of the self, kin, or friends relative to acquaintances, despite reporting substantially greater emotional closeness to friends, consistent with what has been termed a . Kin engendered greater aid than is explicable by affiliative emotion. Participants also reported less anger-yet trends toward greater disgust-when victims were acquaintances relative to all other conditions, replicating prior work distinguishing the social functions of anger and disgust. These results are discussed as they inform both the kinship premium hypothesis and sociofunctional accounts of moral emotion. (PsycInfo Database Record (c) 2023 APA, all rights reserved).