Dunbar argues that gossip does for group-living humans what manual grooming does for other
primates—it allows individuals to service their relationships and thus maintain their alliances on the basis of the principle: ''if you scratch my back, I'll scratch yours.'' Dunbar argues that as humans began living in increasingly larger
social groups, the task of manually grooming all one's friends and acquaintances became so time-consuming as to be unaffordable. In response to this problem, Dunbar argues that humans invented 'a cheap and ultra-efficient form of grooming'—
vocal grooming. To keep allies happy, one now needs only to 'groom' them with low-cost vocal sounds, servicing multiple allies simultaneously while keeping both hands free for other tasks. Vocal grooming then evolved gradually into vocal language—initially in the form of 'gossip'. ==Criticism==