ABSTRACT
This chapter explores that the strategy variously referred to as reciprocal altruism, conditional cooperation or tit-for-tat (TFT) is the only evolutionarily stable strategy (ESS) in an iterated prisoner's dilemma (PD) scenario. John Maynard Smith defines an ESS as 'a strategy such that, if all the members of a population adopt it, then no mutant strategy could invade the population under the influence of natural selection'. The chapter shows that always-defect (AD) is not an ESS, since it is possible for TFT players to invade a population employing AD under the conditions of 'replicator dynamics'. Louis Marinoff has shown that some strategies that incorporate a cooperatively weighted expected-utility maximization (EUM) decision procedure are more successful by several measures of robustness, in certain iterated PD contexts than any member of TFT family of strategies. The subtle forms of morality are generally a product of indirect reciprocity and can be as evolutionarily stable in human society as TFT is in iterated PD's.
