This paper describes the method and the results of a research that Martin Nowak and Karl Sigmund published 1992 in Nature in an article entitled "Tit for tat in heterogeneous populations." Through computer-simulated tournament of iterated prisoner's dilemma, the authors showed that the strategy "Tit for Tat" (TFT) is essential for the emergence of cooperation in a heterogeneous group of players. Their simulation shows that initially mixed population of players evolves to the extinction of almost all strategies except renegades, and then there is a sudden increase in TFT players. Moreover, the simulation shows that TFT is not really the end of evolution, but the beginning of the predominance of a more generous strategy. According to the authors, TFT is a pivot, rather than the end point of an evolution towards cooperation.
