Evolution, partnerships and cooperation

In an evolutionary game theoretic setting, players are allowed to choose not only their strategies for a particular interaction, but also to some extent with whom they will play. A stability concept is presented and examined which allows agents to endogenously construct fixed partnerships. A strategy-matching type is said to be recoverable if a population in which it is used by all players is both internally and externally stable to random mutations. Such a strategy-matching type always exists and maximises social efficiency in the population. Some examples are considered in the light of this concept. The ability to form fixed partnerships enables players to coordinate on efficient outcomes. In particular, cooperation is achieved in the Prisoners' Dilemma without recourse to repetition or rigid spatial restriction.