Human cooperation in the simultaneous and the alternating Prisoner's Dilemma: Pavlov versus Generous Tit-for-Tat.

Abstract

The iterated Prisoner's Dilemma has become the paradigm for the evolution of cooperation among egoists. partners have cooperated with probability Pi = 1, after self cooperated and partner defected with P2 = 0, after self defected and partner cooperated with P3 = 0, and after both defected with P4 = (almost) 1. The greatest difference between Pavlov and Generous TFT appears in P3. Pavlov cooperates with TFT and itself, exploits unconditional cooperators, but it is more heavily exploited by unconditional defectors than TFT. Although there is supporting evidence for TFT-like cooperation from experiments with animals (10-15), no experimental study has tested specifically for Generous TFT or for Pavlov.Models of the evolution of cooperation assumed that the two players make their decisions in synchrony, which seems improbable in many biological situations (6, 7). Although the iterated Prisoner's Dilemma is a suitable model for both simultaneous and alternating choices (16), the most frequent evolutionary outcome has been shown to differ in these situations (6, 7). A Pavlov strategy which does so well in the simultaneous game (5) does rather poorly in the strictly alternating case (6, 7). A kind of Generous TFT [also called "Firm but Fair" (6)] is the predicted evolutionary end product in the alternating game (for the payoff matrix shown in Fig. 1, the winning strategy is described by P1 = 1, P2 = 0, P3 = 1, P4 = 2/3). In the computer simulations, only a memory of one move of both players was allowed for.We did two experiments with first-year biology students at Bern University. Humans (18, 19). The aim of this study was to test specifically whether the strategy that the students use in a simultaneous or an alternating Prisoner's Dilemma is closer to Pavlov or to the Generous TFT described above. A secondary aim was to describe the students' strategies quantitatively so that our results can be used to test for any other strategy that might be predicted in the future. METHODSThe students were assigned to four groups (60% women, similar percentage in each group, X2 = 2.26, df = 3, P = 0.52).Abbreviation: TFT, Tit-for- Tat. 2686

Personal experience and reputation interact in human decisions to help reciprocally

“…In our experiment, as in previous experiments on reciprocity [6,7,8], the aim is to measure effects of first-order information. Hence, subjects do not know whether previous decisions of their interaction partners are based on any information, and it is impossible to examine if a donor reciprocated the earlier decisions of the recipient.…”

Long-term social bonds promote cooperation in the iterated Prisoner's Dilemma

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Fundamental clusters in spatial 2×2 games

“…Even though they are far too simple to capture every detail of such complex interactions, they represent a powerful tool for understanding the characteristics of such encounters. A well-known and well-studied member of these 2 Â 2 games is the Prisoner's Dilemma, which explains the emergence of cooperative behaviour among sel¢sh individuals (see, for example, Axelrod & Hamilton, 1981;Nowak & Sigmund, 1993;Milinski 1987;Wedekind & Milinski 1996;Fehr & Ga« chter 1999 and others). Perhaps even better known to behavioural ecologists is another 2 Â 2 game called Chicken or the HawkD ove game, which describes intraspecies competition (Maynard Smith & Price, 1973).…”