We develop a model for the evolution of preferences guiding behavior in pairwise interactions in groupstructured populations. The model uses the conceptual platform of long-term evolution theory and covers different interaction scenarios, including conditional preference expression upon recognition of interactant’s type. We apply the model to the evolution of semi-Kantian preferences at the fitness level, which combine self-interest and a Kantian interest evaluating own behavior in terms of consequences for own fitness if the interactant also adopted this behavior. We look for the convergence stable and uninvadable value of the Kantian coefficient, i.e., the weight attached to the Kantian interest, a quantitative trait varying between zero and one. We consider three scenarios: (a) incomplete information; (b) complete information and incomplete plasticity; and (c) complete information and complete plasticity, where individuals can, not only recognize the type of their interaction partner (complete information), but also conditionally express the Kantian coefficient upon it (complete plasticity). For (a), the Kantian coefficient tends to evolve to equal the coefficient of neutral relatedness between interacting individuals; for (b), it evolves to a value that depends on demographic and interaction assumptions, while for (c) individuals become pure Kantians when interacting with individuals of the same type, while they apply the Kantian coefficient that is uninvadable in a panmictic population under complete information when interacting with individuals with a different type. Overall, our model connects several concepts for analysing the evolution of behavior rules for strategic interactions that have been emphasized in different and sometimes isolated literatures.
IAST working paper, n. 23-148, January 2023