The author offers the thesis that hunter-gatherers promoted, through cultural means, the playful side of their human nature and this made possible their egalitarian, nonautocratic, intensely cooperative ways of living. Hunter-gatherer bands, with their fluid membership, are likened to social-play groups, which people could freely join or leave. Freedom to leave the band sets the stage for the individual autonomy, sharing, and consensual decision making within the band. Hunter-gatherers used humor, deliberately, to maintain equality and stop quarrels. Their means of sharing had gamelike qualities. Their religious beliefs and ceremonies were playful, founded on assumptions of equality, humor, and capriciousness among the deities. They maintained playful attitudes in their hunting, gathering, and other sustenance activities, partly by allowing each person to choose when, how, and how much they would engage in such activities. Children were free to play and explore, and through these activities, they acquired the skills, knowledge, and values of their culture. Play, in other mammals as well as in humans, counteracts tendencies toward dominance, and hunter-gatherers appear to have promoted play quite deliberately for that purpose.