Abstract
What preferences will prevail in a society of rational individuals when preference evolution is driven by their success in terms of resulting payo§s? We show that when
individualsí preferences are their private information, a convex combinations of selfishness and morality stand out as evolutionarily stable. We call individuals with such
preferences homo moralis. At one end of the spectrum is homo oeconomicus, who acts so as to maximize his or her material payo§. At the opposite end is homo kantiensis, who does what would be ìthe right thing to do,î in terms of material payo§s, if all others would do likewise. We show that the stable degree of morality - the weight placed on the moral goal - equals the index of assortativity in the matching process. The motivation of homo moralis is arguably compatible with how people often reason, and the induced behavior appear to agree with pro-social behaviors observed in many laboratory experiments.