Abstract
Third-party punishment—the targeted infliction of costs on behalf of another by an unaffected third party—has been demonstrated in several species, including humans. Here I propose that one of the functions of third-party punishment is to deter future harm to victims with whom the punisher’s welfare is interdependent. Additionally, I propose that this function is governed by psychological mechanisms that use internal regulatory variables called welfare trade-off ratios (WTRs) to guide social behavior via their outputs to motivational systems. Specifically, I propose that WTRs are used by the psychological mechanisms that regulate whether witnesses become angry in response to harms imposed on others, and thus, that they are key components of the system(s) that regulate third-party punishment. The goal of this dissertation was to test the causal role of welfare interdependence in third-party punishment by manipulating two WTR-relevant cues that were expected to raise subjects’ WTR toward a partner who was initially a stranger, and then creating a situation in which the partner was harmed by another stranger, followed by an opportunity for the subject to punish the transgressor. In a laboratory experiment with 250 subjects, neither manipulation significantly affected subjects’ WTRs for their partners. However, a noteworthy finding from this experiment is that there was not a significant amount of third-party punishment, which adds to a growing body of evidence suggesting third-party punishment on behalf of strangers is rare.