When do individuals maximize their inclusive fitness?
Adaptation is often described in behavioral ecology as individuals maximizing their inclusive fitness. Under what conditions does this hold and how does this relate to the gene-centered perspective of adaptation? We unify and extend the literature on these questions to class-structured populations. From a gene-centered perspective, we demonstrate that uninvadable traits (meaning that all deviating mutant go extinct) can be characterized as maximizing the average over classes of either
... ific average direct fitness or of class-specific inclusive fitness. These two fitness measures are defined as reproductive-value weighted averages over distributions of demographic and genetic contexts. These distributions usually depend on events in previous generations, and are thus not under individual control, which prevents, in general, from envisioning individuals as autonomous fitness maximizers. For weak selection in uninvadable population states, however, the dependence of the contextual distributions on earlier events can be neglected, and then all individuals in all classes can be envisioned as inclusive fitness maximizers (but not generally as average direct fitness maximizers). This defines an individual-centered perspective of adaptation and justifies, as a first-order approximation, the long-heralded perspective of individuals appearing to maximize their inclusive fitness.