Players' rationality and prisoners' dilemma game

In this paper we assume explicitly that a player has an incentive to a coop erative behavior in prisoners' dilemma game and try to explain the realizat ion of cooperative behavior. In addition to the usual utility-maximizer, we add some types of players who have a tendency to a cooperative behavior an d show that some of the latter types contribute the realization of cooperat ion in a long period of interaction. Further in the replicator dynamics of the average payoff game it is shown that as the time goes to infinity the r atio of the selfish type decreases to 0% and that of Sticky Tit-for-Two-Tat s (STF2T) increases. Also we propose a new learning model where the ratio o f the selfish type remains the same and that of cooperative type increases in terms of STF2T.