Altruism and Indirect Reciprocity: The Interaction of Person and Situation in Prosocial Behavior

A persistent puzzle in the social and biological sciences is the existence of prosocial behavior, actions that benefit others, often at a cost to oneself. Recent theoretical models and empirical studies of indirect reciprocity show that actors behave prosocially in order to develop an altruistic reputation and receive future benefits from third parties. Accordingly, individuals should stop investing in reputations via prosocial behavior when a future benefit (via indirect reciprocity) is unlikely. The conclusion that the absence of reputational incentives necessarily leads to egoistic behavior contrasts sharply with models of heterogeneous social preferences. Such models demonstrate the theoretical plausibility of populations composed of egoists and altruists. Results of Study 1 show that actors classified a priori as egoists respond strategically to reputational incentives, whereas those classified a priori as altruists are less affected by these incentives. While egoists act prosocially when reputational incentives are at stake but not when opportunities for indirect reciprocity are absent, altruists tend to act prosocially regardless of whether reputational incentives are present. These results suggest that apparently altruistic behavior can result from non-strategic altruism or reputation-building egoism. Study 2 demonstrates the robustness of these results and explores indirect reciprocation of others’ prosocial acts. The results show that altruists indirectly reciprocate at higher levels than egoists, and individuals tend to discount others’ prosocial behaviors when they occur in the presence of reputational incentives. As a result, public prosocial behaviors are indirectly reciprocated less than private prosocial behaviors. In line with our argument that altruists pay less attention to reputational incentives, egoists showed a greater tendency than altruists to discount others’ public prosocial behaviors. The results support the growing focus on heterogeneity of individuals’ social preferences in models of altruism and indirect reciprocity. Altruism and Indirect Reciprocity: The Interaction of Person and Situation in Prosocial Behavior Humans display a wide array of prosocial behaviors, actions that benefit others, often at a cost to oneself. For decades, scholars have drawn on theories of kin selection (Hamilton 1964) and reciprocal altruism (Trivers 1971) to explain such actions. But much prosocial behavior is directed at unrelated strangers who may be unable to reciprocate at some later time, which presents an anomaly for both explanations. To explain prosocial behavior among unrelated individuals in large populations, researchers turned their attention to models of indirect reciprocity (Alexander 1987; Nowak 2006; Panchanathan and Boyd 2004; Rockenbach and Milinski 2006; Wedekind and Milinski 2000), which account for the possibility that individuals receive long-term benefits for short-term prosocial acts. Both field work (Smith and Bird 2000) and laboratory studies (Milinski et al. 2002a; 2002b) support the notion that individuals confer important advantages on those who act prosocially toward others, i.e., they reciprocate benefactors indirectly. Furthermore, research shows that potential benefactors respond strategically to the presence or absence of these benefits, cooperating at higher levels when reputational benefits and possibilities of indirect reciprocity exist versus when they do not (Milinski et al. 2002b; Semmann et al. 2004). The presence or absence of opportunities for indirect reciprocity thus may explain much of prosocial behavior. But here we build on existing models of heterogeneous social preferences to show that indirect reciprocity approaches miss a very important piece of the prosociality puzzle and, as a result, under-predict the occurrence of prosocial behavior when opportunities for indirect reciprocity do not exist. Specifically, we show that whereas some individuals (here referred to as “egoists”) behave prosocially only when reputational incentives encourage the