The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)


The functions of mutual grooming among wild chimpanzees

ZARIN P. MACHANDA1, IAN C. GILBY2 and RICHARD W. WRANGHAM1.

1Department of Human Evolutionary Biology, Harvard University, 2Department of Evolutionary Anthropology, Duke University

Thursday 9:30-9:45, Galleria South Add to calendar

Although grooming has been extensively studied among non-human primates, these studies have almost all focused on explaining patterns of uni-directional grooming (when individual A grooms individual B, and B does not groom A) and not mutual grooming (when two individuals simultaneously groom each other). This is surprising given that mutual grooming occurs in a number of primate species at varying frequencies suggesting that mutual grooming and uni-directional grooming serve different functions from one another. In this study, we used 17 years of data from the Kanyawara community in Kibale National Park, Uganda to examine patterns of mutual grooming among wild chimpanzees. We specifically tested the hypothesis that mutual grooming functions in the maintenance of social bonds. We found that adult males, who typically form stronger social bonds than females, were more likely to groom each other mutually when compared to female-female dyads. In addition, among male-male dyads, those that exhibited characteristics of strong social bonds, such as high rates of association and low rates of aggression, also engaged in mutual grooming more frequently than dyads with weak social bonds. These results suggest that mutual grooming functions to support the formation of social bonds among chimpanzees. We also found evidence that mutual grooming is a more efficient form of uni-directional grooming. This may allow chimpanzees to offset the opportunity cost of uni-directional grooming, especially when food is less available and there may not be as much time available to devote to social activities.

This study was funded by the National Science Foundation, Grant 0416125

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