Chimpanzees Groom

Bi-directional (or simultaneous mutual) grooming is unusually common among chimpanzees (though rare in other primates) suggest that this might be because it is an especially strong indicator of social bonding

Data on the dynamics of grooming interactions from a captive group of chimpanzees (Pan troglodytes) to show that dominant individuals tolerated the individuals with whom they performed bi-directional grooming more than they did those who typically provided them unidirectional grooming. Dominants rejected and terminated grooming sessions more often with the individuals who provided them with mostly unidirectional grooming than with those with whom they groomed bi-directionally. In addition, animals engaged in bi-directional grooming more often with both relatives and those with whom they were often in proximity. These results support the bonding model of mutually reciprocated grooming at the expense of the Reciprocal Altruism model, and suggest that, at least in chimpanzees, simultaneous mutual grooming may play a particularly important role in social bonding."

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