UC San Diego

Human society is built on cooperative relationships. Humans have evolved sophisticated mental representations and mechanisms to cooperate effectively in a noisy and changing world. One such representation is the welfare tradeoff ratio (WTR)—the weight one places on another person’s welfare relative to her own. People not only use WTRs to make social decisions consistently in varying circumstances, but can also infer others’ WTRs from their actions, allowing them to reciprocate by adjusting their own WTRs. In this dissertation, I investigate the mechanisms underlying the dynamics of WTRs and build tools to support such investigation. In Chapter 1, I develop an accurate and efficient measure of WTRs, called the Lambda Slider, which, in contrast to previous measures, requires only one response from participants. In three experiments, I show that the Lambda Slider has high reliability and validity, enabling fine-grained investigation of the dynamics of WTRs over time or space. In Chapter 2, I explore the evolutionary origins of the capacity of WTR inference, a basic form of “theory of mind” that supports reciprocity and partner choice. Through evolutionary game simulations, I identify two environmental requirements for WTR inference to evolve—stable opponents and variable payoff structures. Using behavioral experiments, I show that people do perform WTR inference in such an environment. In Chapter 3, I strengthen the argument in Chapter 2 byfocusing on games without strong interdependence, a more common occurrence in the real world, and considering reciprocity in the form of WTR inference and adjustment. I found that a reciprocal agent with WTR inference performs the best in both noiseless and noisy environments, but has a unique advantage only in a noisy environment with uncertainty about the payoffs perceived by the opponent. This points to the role uncertainty plays in the evolution of theory-of-mind capacities. In Chapter 4, I discuss some future directions. Overall, this work lays the groundwork for studying the dynamics of WTRs in a fine-grained way and understanding the evolution of sophisticated mental representations underlying people’s social life.