Altruism, the prisoner's dilemma, and the components of selection

The n-player prisoner's dilemma (PD) is a useful model of multilevel selection for altruistic traits. It highlights the nonzero-sum interactions necessary for the evolution of altruism as well as the tension between individual and group-level selection. The parameters of the n-player PD can be directly related to the equation due to Price (1970) as well as to a useful alternative selection decomposition. Finally, the n-player PD emphasizes the expected equilibrium condition of mutual defection in the absence of higher levels of organization and selection.