Punitive sentiment as an anti-free rider psychological device

Those who contribute to a public good sometimes experience punitive sentiments toward others. But is the system that produces these sentiments an adaptation and, if so, which collective action problem was it designed to solve? Prior results from experimental economics show that acts of free riding are sometimes punished; that punishment deters free-riding; and that the risk or actuality of punishment recruits higher levels of cooperation in a joint effort. This suggests that one function of punitive sentiments could be to recruit labor for collective actions. However, adaptations designed to cause participation in collective actions could not have evolved unless there were some mechanism that protected those who participated from having lower fitness than non-participating free riders. Therefore, a second possible function of punishment could be to eliminate or reverse fitness differentials that favor free rider designs over participant designs. To map the computational structure of this motivational adaptation (and hence identify its specific function) requires data that relate an individual’s circumstances to his or her desire to punish. Herein we report such data. The results indicate that the computational system that regulates one’s level of punitive sentiment in collective action contexts is functionally specialized for removing the fitness advantage enjoyed by free riders, rather than for labor recruitment or other functions. Results also support the hypothesis that a separate pro-reward motivational system exists that appears designed to handle the problem of labor recruitment. Rational choice counterexplanations for punitive sentiments were considered, but eliminated on the basis of the evidence.