Metagames : the evolution of game-changing traits

Cooperative social behaviours are ubiquitous in nature and essential to biological theory, yet they present an apparent paradox since cooperators benefit others while potentially incurring a fitness cost. The standard resolution is that cooperation is evolutionarily stable if cooperative behaviours are positively assorted, so their benefits are directed at other cooperators, shifting the problem to explaining the presence of positive assortment. If we view individuals as playing an evolutionary game, then the evolution of assorting traits changes the rules of the game to allow for greater cooperation. This is one of many ways that individuals can evolve game-changing traits that modify their social niche, since social interactions occur in social environments that are in part the product of evolved traits. We investigate this by introducing a game-theoretic model of metagames where the evolution of individual strategies changes the social game. Because of mathematical equivalences between game-changing mechanisms and pay off matrix transformations, we can use metagames as a common framework to model the coevolution of social games and social conditions. Instead of simply identifying the conditions under which cooperation evolves, metagames explain how these conditions arise by identifying the circumstances under which the conditions for cooperation evolve. While positive assortment on social traits is necessary for cooperation to be stable, we show that alone it will only allow game-changing traits promoting cooperation to evolve when cooperation is already favoured. This is insuffi?cient to explain the evolution of assortment in the Prisoner's Dilemma. We find that much as assortment on social traits is crucial to the evolution of cooperation, assortment on game-changing traits is crucial to the evolution of social assortment. Because assortment on social and game-changing traits are connected, this assortment has been hidden in existing accounts. We are able to characterise the relationship between the two types of assortment, and show how assortment on game-changing traits can enable the evolution of social assortment. We can therefore explain the evolution of the conditions assumed necessary for the evolution of cooperation.