SUMMARY In my studies on some subtropical and tropical polistine wasps (Hymenoptera), it was shown that (i) social relations among cofoundresses are far milder than those reported so far in other polistine wasps, (ii) more than one female often lay eggs in a nest even after the emergence of the first brood females (workers), and (iii) aggressive behaviours among females of two Mischocyttarus and possibly one or two Ropalidia species drastically escalate after the emergence of first brood adults (this is considered to occur between the foundresses and their daughters). These observations suggest a hypothesis that the permanently pleometrotic (multi-queen) societies in the vespids evolved through a selfish aggregation of foundresses and manipulation of daughter wasps by the group of foundresses. The switch-over from functional differentiation among communally nesting females to mother-daughter caste systems suggested by MICHENER (1958, 1974) can be explained, in part, by this hypothesis.