Extraordinary Self-Sacrifice

Abstract

Theories of self-sacrifice ordinarily assume that actors will have larger fitness effects on recipients than on themselves. There are, however, conditions in which actors can pay costs that exceed the altruistic benefits they provide or the spiteful costs they impose. In a spatially structured population, I show that such \"extraordinary\" self-sacrifice evolves when actors use information about kinship and dispersal to maximize inclusive fitness. The result can be described by a simple rule: extraordinary self-sacrifice evolves when the actors neighbors are kin and the recipients neighbors are not.