What preferences or moral values should one expect evolution to favor? We provide a generalized de…finition of evolutionary stability of heritable traits in arbitrarily large aggregative interactions under random matching that may be assortative. We establish stability results when these traits are strategies in games, and when they are preferences or moral values in games in which each player’s preferences or moral values are the player’’s private information. We show that certain moral preferences, of a kind that exactly re‡flects the assortativity in the matching process, are evolutionarily stable. In particular, selfi…shness is evolutionarily unstable as soon as there is any assortativity. We also establish that evolutionarily stable strategies are the same as those played in equilibrium by rational individuals with evolutionarily stable moral preferences. We provide simple operational criteria for evolutionary stability and apply these to canonical examples.

Joint work with Jörgen W. Weibull

Keywords: Evolutionary stability, assortativity, morality, homo moralis, public goods, contests, helping.

JEL codes: C73, D01, D03.