Cooperation and the Prisoner's Dilemma: towards testable models of mutualism versus reciprocity

For the purpose of distinguishing between mutualism and reciprocity in nature, recent work on the evolution of cooperation has both oversimplifed and undersimplified the distinction between these two categories of cooperation. This article addresses the resulting issues of model testability, clarifies the role of time and argues that the category of 'pseudo-reciprocity' is an unnecessary complication. (C) 1997 The Association for the Study of Animal Behaviour.