Cooperating for direct fitness benefits

Abstract

Among the great variety of highly stylized models for the evolution of cooperation, some are actually sharpening our eyes. The Prisoner’s Dilemma, for example, helps us understand ‘free riding’ and the difference between oneshot and repeated interactions; Hamilton’s basic kin selection model for the evolution of altruism highlights the role of genetic correlations among interacting individuals, etc. What fruitful models of this kind create is a sensitivity to factors that might be crucial to understanding real cases of cooperation. Lehmann & Keller (2006, L&K) rightly emphasize that the identification of selective forces for cooperation can be obscured if one fails to sharply distinguish between these factors. L&K classify the factors into four categories, the first being direct fitness benefits to a cooperator. We wish to extend their argument by focusing on this first category, drawing attention to important further distinctions that arise from taking biological facts and a broader theoretical background into account. Our commentary emphasizes the scope of direct fitness benefits in cooperation and discusses ways of unfolding the richness of phenomena captured by this category. If one accepts, as seems likely to be true, that the great range of mutualistic species interactions and the mindboggling integrated complexity of cells and organisms are largely products of direct fitness benefits, it is rather surprising how little effort has gone into modelling these forms of cooperation, compared with the arguably much smaller categories of reciprocity or interactions among relatives, not to mention green-beard genes. We wish to point to important ideas and mention some open questions about the role of direct fitness benefits in the evolution of cooperation.