Abstract: We live in a society. Societies depend on cooperation between unrelated individuals who have little prospect for repeated interactions––and thus little clear incentive to cooperate. How can we resolve this conundrum? One plausible mechanism is indirect reciprocity: I cooperate with someone because I know, whether by direct observation or by secondhand information, that they have behaved well toward others in the past. In doing so, I may in turn become a recipient of future cooperative acts. Indirect reciprocity is critical in a digital world; much of what we do and say is publicly accessible, and information about our reputations can easily be broadcast.
I use evolutionary game theory and adaptive dynamics to tackle fundamental questions in the theory of indirect reciprocity. How can societies transition from idiosyncratic individual judgments to shared consensus opinions? How do societies converge on a common set of rules for how to assign moral standing? How should we aggregate information from multiple social contexts when deciding how to treat others? I present both encouraging and troubling implications of my results, as well as next steps for research into this exciting mechanism.