When Reciprocity is not Enough : Explaining Anti-Social Outcomes via Intrinsic Personality Traits

Behavior and outcomes that do not fit to classical game theory are often observed and, hence, reported. Common explanations for that are, e.g., repeated games, reciprocity, costly punishment, and pure altruism. Via the prisoner's dilemma and costly punishment, we show that those explanations, esp. reciprocity, are not always able to account for outcomes that involve anti-social punishment, i.e., to punish someone after a successful cooperation. We demonstrate, however, that intrinsic motivations, including both altruism and spiteful preferences, additional to material payoffs can explain those outcomes. To capture the agents' intrinsic motivation we introduce a uniform notion of altruism and sadism, the so-called SEA model. Further, we present a Python code to find so-called (pure-strategy) SEA Nash equilibria. Conclusively, we illustrate the SEA model via simple, well-known games.