Social evolution in structured populations

Understanding the evolution of social behaviours such as altruism and spite is a long-standing problem that has generated thousands of articles and heated debates. Previous theoretical studies showed that whether altruism and spite evolve may be contingent on seemingly artificial model features, such as which rule is chosen to update the population (for example, birth-death or death-birth), and whether the benefits and costs of sociality affect fecundity or survival. Here we unify these features in a single comprehensive framework. We derive a general condition for social behaviour to be favoured over non-social behaviour, which is applicable in a large class of models for structured populations of fixed size. We recover previous results as special cases, and we are able to evaluate the relative effects of benefits and costs of social interactions on fecundity and survival. Our results highlight the crucial importance of identifying the relative scale at which competition occurs.