ABSTRACT
Kinship has been the central construct in evolutionary biological analyses of social phenomena since Hamilton (1964) extended the concept of Darwinian fitness (personal reproductive success) to encompass the actor’s effects on the expected reproduction of collateral as well as descendant kin (“inclusive fitness”). Hamilton’s theory replaced the classical Darwinian conception of organisms as evolved “reproductive strategists” with the more subtle notion that they have evolved to be “nepotistic strategists,” instead. If each of a behaving animal’s genes is just as likely to be duplicated in a sister as in a daughter, for example, then the evolution of sororal beneficence is not, in principle, more paradoxical than the evolution of maternal beneficence. No development in this century has more pervasively and fundamentally affected biologists’ understandings of social influence and interaction.
