The naked mole-rat (Heterocephalus glaber) occupies an unusual place among social vertebrates. Like the other species considered in this volume, naked mole-rats are cooperative breeders. These small, virtually hairless rodents live in subterranean colonies in which nonreproductive individuals routinely groom, feed, and protect the offspring of reproductive colony members (Jarvis 1981, 1991; Lacey & Sherman 1991). At the same time, naked mole-rats are eusocial, meaning “truly social” (Batra 1966). Although this term has generally been reserved for insect societies (e.g., ants, termites, and some bee and wasp species) in which there is “cooperation in caring for the young, reproductive division of labor with more or less sterile individuals working on behalf of individuals engaged in reproduction, and overlap of at least two generations of life stages capable of contributing to colony labor” (Hölldobler & Wilson 1990, p. 638), H. glaber also exhibits these diagnostic characteristics. Consequently, evolutionary explanations for both cooperative breeding and eusociality must apply to naked mole-rats.
Although characterizing H. glaber as cooperatively breeding and eusocial seems redundant, this dual description is currently necessary because of the apparent divergence between studies of social evolution in vertebrates and invertebrates. Despite repeated attempts to draw attention to behavioral similarities between eusocial insects and cooperatively breeding birds and mammals (e.g., Vehrencamp 1979; Andersson 1984; Alexander, Noonan, & Crespi 1991; Emlen et al. 1991; Lacey & Sherman 1991; Krebs & Davies 1993), studies of vertebrate and invertebrate sociality have proceeded more or less independently.