How Altruism Can Prevail in an Evolutionary Environment

This paper considers a series of examples in which evolution supports cooperative behavior in single-shot prisoners' dilemma. Examples include genetic inheritance for asexual siblings and for sexual diploid siblings. We also study two models of ``cultural inheritance''; one in which siblings copy either their parents or an extrafamilial role model and one in which neighbors arrayed along a circular road copy successful neighbors. Finally, we consider a model in which parents choose their behavior, realizing that it may be imitated by their children. A unifying principle in these models is that cooperative behavior more is likely to be sustained in environments where relatively successful organisms are copied relatively often and where organisms that have the same role model are more likely to interact with each other than with a randomly selected member of the population.