Abstract

We describe more precise definitions for the term “eusociality” and other social systems. Our criterion for eusociality is the presence of castes, which are groups of individuals that become irreversibly behaviorally distinct at some point prior to reproductive maturity. Eusocial societies are characterized by two traits: (1) helping by individuals of the less-reproductive caste, and (2) either behavioral totipotency of only the more reproductive caste (facultative eusociality) or totipotency of neither caste (obligate eusociality). We define “cooperative breeding” as alloparental care without castes. Cooperatively breeding societies may comprise two types, semisocial (distribution of lifetime reproductive success bimodal), and quasisocial (distribution of lifetime reproductive success unimodal), but this hypothesis requires empirical analysis. Our definitions conceptually unify studies of arthropod and vertebrate sociality.

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