Cooperation

Abstract: Cooperation among unrelated individuals can evolve not only via reciprocal altruism but also via trait-group selection or by-product mutualism (or some combination of all three categories). Therefore the (iterated) prisoner's dilemma is an insufficient paradigm for studying the evolution of cooperation. We replace this game by the cooperator's dilemma, which is more versatile because it enables all three categories of cooperative behavior to be examined within the framework of a single theory. Controlled studies of cooperation among fish provide examples of each category of cooperation. Specifically, we describe reciprocal altruism among simultaneous hermaphrodites that swap egg parcels, group-selected cooperation among fish that inspect dangerous predators and by-product mutualism in the cooperative foraging of coral-reef fish.

Abstract: Darwinian selection should preclude cooperation from evolving; yet cooperation is widespread among organisms. We show how kin selection and reciprocal altruism can promote cooperation in diverse 2×2 matrix games (prisoner’s dilemma, snowdrift, and hawk-dove). We visualize kin selection as non-random interactions with like-strategies interacting more than by chance. Reciprocal altruism emerges from iterated games where players have some likelihood of knowing the identity of other players. This perspective allows us to combine kin selection and reciprocal altruism into a general matrix game model. Both mechanisms operating together should influence the evolution of cooperation. In the absence of kin selection, reciprocal altruism may be an evolutionarily stable strategy but is unable to invade a population of non-co-operators. Similarly, it may take a high degree of relatedness to permit cooperation to supplant non-cooperation. Together, a little bit of reciprocal altruism can, however, greatly reduce the threshold at which kin selection promotes cooperation, and vice-versa. To properly frame applications and tests of cooperation, empiricists should consider kin selection and reciprocal altruism together rather than as alternatives, and they should be applied to a broader class of social dilemmas than just the prisoner’s dilemma.

Abstract: Cooperation, mutually beneficial activities involving members of the same, or of different, species, allows evolution of versatile individuals and complex, competitive ecosystems. Social cooperation involves members of the same, mutualism of different, species. Elaborate social cooperation involves division of labor; mutualism often involves the exchange of goods for services, as when corals offer algal symbionts fertilizer and safe homes in return for carbohydrates. Such cooperators risk being cheated by individuals that accept benefits from partners without reciprocating. The central problem in understanding how cooperation evolves is how cheating is controlled. Cooperators have found many ways to restrict cheating.

Abstract: Cooperation is defined as any adaptation that has evolved, at least in part, to increase the reproductive success of the actor's social partners. Inclusive fitness theory reveals that cooperation can be favoured by natural selection owing to either direct fitness benefits (mutually beneficial cooperation) or indirect fitness benefits (altruistic cooperation). Direct fitness benefits can arise as a simple byproduct of cooperation, or else owing to the existence of enforcement mechanisms, which may be fixed or conditioned according to the individual's cooperative behaviour. Indirect fitness benefits can arise when cooperation occurs between genetically similar individuals, as a consequence of limited dispersal, kin discrimination or greenbeard mechanisms. These theoretical mechanisms are illustrated with empirical examples, from laboratory experiments to field studies. Key concepts: The function of Darwinian adaptation is to maximize the organism's inclusive fitness. Inclusive fitness describes how well an organism transmits copies of its genes to future generations. Direct fitness is the part of inclusive fitness that comes from the organism's own reproductive success. Indirect fitness is the part of inclusive fitness that comes from the reproductive success of the organism's genetic relatives. Cooperation is any adaptation whose function is, at least in part, to increase the reproductive success of a social partner. Cooperation is mutually beneficial if the actor also benefits and altruistic if the actor suffers a net loss of reproductive success. Mutually beneficial cooperation is favoured by direct fitness benefits. Direct fitness benefits can arise as a byproduct or owing to enforcement mechanisms. Altruistic cooperation is favoured by indirect fitness benefits. Indirect fitness benefits can arise as a consequence of limited dispersal, kin discrimination or greenbeard mechanisms. Keywords: altruism; Hamilton's rule; inclusive fitness; kin selection; social evolution