Evolution of Semi-Kantian Preferences in Two-Player Assortative Interactions with Complete and Incomplete Information and Plasticity

Ingela Alger, and Laurent Lehmann


We model the evolution of preferences guiding behavior in pairwise interactions in group-structured populations. The model uses long-term evolution theory to examine different interaction scenarios, including conditional preference expression upon recognition of the partner’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 partner also adopted this behavior. We seek 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 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 generally evolves 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) there are generally multiple uninvadable types, including the type whereby an individual is a pure Kantian when interacting with individuals of the same type and applies the Kantian coefficient that is uninvadable under complete information with zero relatedness when interacting with a different typed individual. 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 studies.


Evolution of semi-Kantian preferences; Group-structured populations; Fitness; Convergence stability; Uninvadability; Homo moralis;


Ingela Alger, and Laurent Lehmann, Evolution of semi-Kantian preferences in two-player assortative interactions with complete and incomplete information and plasticity, IAST Working Paper, n. 23-148, January 2023, revised May 2023.

Published in

Dynamic Games and Applications, vol. 13, December 2023, p. 1288–1319