Abstract

During human evolution, individuals interacted in groups connected by limited migration and sometimes conflicts. If the spread of preferences, from one generation to the next, depends on their material success, which preferences will prevail? Building on population biology models of spatially structured populations, and assuming preferences to be private information, we characterize which preferences, if any, cannot be displaced, once established. We find that such uninvadable preferences represent different motives when expressed in terms of fitness than when expressed in terms of material payoffs. At the fitness level, individuals appear be driven by a mix of self-interest and a Kantian motive, which involves evaluating one’s behavior in light of what own fitness would be if others were to choose the same behavior. This Kantian motive is borne out from kin selection (be it genetic or cultural). At the material payoff level, individuals appear to be driven by these two motives, but also in part by an other-regarding motive towards own group members. This motive represents within-group spite or altruism. We show how population structure – group size, migration rates, probability of group conflicts, cultural loyalty towards parents- shape the relative importance of these motives.

Co-authors : Jörgen W. Weibull, Laurent Lehmann

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