I hypothesize that three conditions, (1) food-shelter coincidence, (2)
strong selection for defense, and (3) ability to defend, are sufficie
nt, although not necessary, for the evolution of eusociality in group-
living animals. Reasons for this association between ecology and eusoc
iality include extremely high value of the habitat, possibilities for
habitat inheritance, high relatedness in claustral situations, self-su
fficiency of juveniles, greater ability of workers to reproduce, and t
rade-offs between defensive ability and dispersal.