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Abstract

Cooperation is at the heart of life on Earth. It binds together organisms, families, and societies. One of the most ubiquitous tools for studying cooperation is game theory, which has revolutionized the field of social behavior research. This thesis explores how theoretical and experimental methods can contribute to our understanding of the different mechanisms and benefits by which cooperation evolves. The first three chapters focus on a core mechanism of cooperation: direct reciprocity. When individuals know that there is a high probability of future interactions, they benefit from maintaining a cooperative relationship. These repeated interactions allow individuals to exchange favours and build a mutually beneficial relationship that leaves everyone better off. Chapter 2begins with a review of the theoretical and experimental literature, which highlights some important gaps in our understanding of direct reciprocity. In particular, we argue that theoretical studies often fail to predict which reciprocal strategies humans use to maintain cooperation. One possible reason may be that most of these models and experiments study interactions in isolation, whereas most of human social life is much more complex. Thus, in Chapter 3, we investigate direct reciprocity in multi-game settings, where individuals take part in two concurrent interactions with the same or different partners. Using both evolutionary simulations and a behavioral experiment, the results show that individuals are able to link games when it makes strategic sense. We also show that cognitive biases are crucial for predicting human behavior. Chapter 4 develops a different type of reciprocal strategy that does not rely on explicit and exact memory of the game history. Instead, it embodies more realistic cognitive abilities of human players, as revealed by a behavioral experiment. The last two chapters examine how the importance of finding cooperative partners can explain different social behaviours. Chapter 5 reviews the literature on how different types of cues signal cooperativeness. Behavioral cues based on past behavior have been found to be accurate predictors of cooperativeness and they are perceived as such by third parties. One such behavior is acting according to moral values. A behavior is considered principled if individuals display it consistently, regardless of the costs and without compromise. The Chapter 6 builds on this finding by developing a signaling model to analyze principled behavior. The act of consistently abiding to one’s principles enhances an individual’s reputations for trustworthiness and makes them a preferred cooperative partner. Given the social benefits of principled behavior, game theory and evolutionary principles can show how the dynamics of partner choice can lead individuals to display seemingly maladaptive behavior. Overall, the thesis offers a comprehensive examination of cooperation in reciprocal relationships, bridging theoretical insights with empirical observations to deepen our understanding of human social interactions.