Moral systems are described as systems of indirect reciprocity, existing because of histories of conflicts of interest and arising as outcomes of the complexity of social interactions in groups of long-lived individuals with varying conflicts and confluences of interest and indefinitely iterated social interactions. Although morality is commonly defined as involving justice for all people, or consistency in the social treatment of all humans, it may have arisen for immoral reasons, as a force leading to cohesiveness within human groups but specifically excluding and directed against other human groups with different interests.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74712/1/j.1467-9744.1985.tb00574.x.pd