Eusociality (Greek eu: "good/real" + "social") is a term used for the highest level of social organization in a hierarchical classification.
The lower levels of social organization, presociality, were classified using different terms, including presocial, subsocial, semisocial, parasocial and quasisocial.
The most familiar examples are social insects such as ants, bees, and wasps (order Hymenoptera), as well as termites (order Isoptera), all with reproductive queens and more or less sterile workers and/or soldiers. The only mammalian examples are the naked mole rat and the Damaraland mole rat.
Eusociality with biologically sterile individuals represents the most extreme form of kin selection. The analysis of eusociality played a key role in the development of theories in sociobiology.
The phenomenon of reproductive specialization is found in various organisms. It generally involves the production of sterile members of the species, which carry out specialized tasks, effectively caring for the reproductive members. It can manifest in the appearance of individuals within a group whose behavior (and sometimes anatomy) is modified for group defense, including self-sacrificing ("altruism").
The term "eusocial" was introduced in 1966 by Suzanne Batra and given a more definitive meaning by E. O. Wilson. It was originally defined to include those organisms (originally, only invertebrates) that had certain features:
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