Eusociality: from the first foragers to the first states. Introduction to the special issue.

People have always been social. Ethnographic evidence suggests that transfers of food and labor are common among contemporary hunter-gatherers, and they probably were common in Paleolithic groups. Archaeological evidence suggests that cooperative breeding went up as we settled down: as territory defenders became more successful breeders, their helpers' fertility would have been delayed or depressed. And written evidence from the Neolithic suggests that the first civilizations were often eusocial; emperors fathered hundreds of children, who were provided for and protected by workers in sterile castes. Papers in this issue of Human Nature look at helpers and workers across the eusociality continuum--from hard-working grandmothers and grandfathers, to celibate sisters and brothers, to castrated civil servants--from the first foragers to the first states.