Since 1981, the iterated Prisoner’s Dilemma has dominated studies of non-kin cooperation. Alternative models have received relatively little attention. The simplest alternative is mutualism, in which mutual cooperation always pays best. The behaviour of three pairs of blue jays, Cyanocitta cristata, was tested in precisely controlled iterated mutualism and Prisoner’s Dilemma games. Although the jays readily cooperated in the mutualism game, cooperation neither developed nor persisted in a Prisoner’s Dilemma. No empirical justification was found for the status of the iterated Prisoner’s Dilemma as the basic paradigm of non-kin cooperation.
Bibliographical noteFunding Information:
We thank L. Dugatkin, T. Getty, A. Kacelnik, A. Kamil, J. Krebs, M. Mesterton-Gibbons, K. Nishimura, M. Nowak and two anonymous referees for their advice; J. Anderson, W. Beachly, J. Kren, J. Robson and K. Toyer for helping with the experiment; and the National Science Foundation (BNS-8958228), Lincoln Telephone Company and the CliV Charitable Foundation for financial support.