Experimental and theoretical investigations of the emergence and sustenance of prosocial behavior in groups

The general goal of this thesis was to study conditions under which prosocial behavior is established and maintained. I approached these questions by applying predictions and assumptions of evolutionary game theory to human cooperation within experimental settings. Cooperative behavior is an evolutionary puzzle, because over time natural selection should favor cheating behavior. Nevertheless, cooperation is ubiquitous in nature. Cooperative behavior is costly and provides benefits to other individuals, whereas cheating - or defection - does not incur costs but offers benefits allocated by cooperative behavior of others. Thus, cooperation cannot be an evolutionary stable strategy without special mechanisms that can reduce the chance of exploitation. In this thesis, I examined (i) the effects of multiple interactions on reciprocal behavior, and (ii) the impact of social structure on dyadic relationships using the prisoner’s dilemma paradigm. Additionally, (iii) I investigated the effect of punishment, which can trigger conflict escalation, in a public goods game. In Chapter 1, I investigated whether and in which way different numbers of social interaction partners affect cooperative behavior in the iterated prisoner’s dilemma (IPD). In line with the concept of direct reciprocity, I found that participants in the traditional IPD with an unknown ending frequently cooperated. Overall, behavior most closely followed reactive strategies close to generous tit-for-tat ...