  Prosocial behaviors are encountered in the donation game, the prisoner's
dilemma, relaxed social dilemmas, and public goods games. Many studies assume
that the population structure is homogeneous, meaning all individuals have the
same number of interaction partners, or that the social good is of one
particular type. Here, we explore general evolutionary dynamics for arbitrary
spatial structures and social goods. We find that heterogeneous networks,
wherein some individuals have many more interaction partners than others, can
enhance the evolution of prosocial behaviors. However, they often accumulate
most of the benefits in the hands of a few highly-connected individuals, while
many others receive low or negative payoff. Surprisingly, selection can favor
producers of social goods even if the total costs exceed the total benefits. In
summary, heterogeneous structures have the ability to strongly promote the
emergence of prosocial behaviors, but they also create the possibility of
generating large inequality.
