Association patterns among wild chimpanzees (Pan troglodytes schweinfurthii) reflect sex differences in cooperation

  • Ian C. GilbyEmail author
  • Richard W. Wrangham
Original Paper


Theory predicts that frequent dyadic association should promote cooperation through kin selection or social tolerance. Here we test the hypothesis that sex differences in the strength and stability of association preferences among free-ranging chimpanzees conform to sex differences in cooperative behavior. Using long-term data from the Kanyawara chimpanzee (Pan troglodytes schweinfurthii) community (Kibale National Park, Uganda), we calculated indices of intra-sexual dyadic association over a 10-year period. We found that (1) male–male dyads had significantly stronger association indices than female–female dyads, (2) the pattern of association preferences in both sexes changed little over the entire study period, and (3) when comparing periods with different alpha males, changes in association strength were more frequent among males. These results demonstrate that both the strength and stability of association patterns are important components of social relationships. Male chimpanzees, which are characterized by frequent cooperation, had association preferences that were both strong and stable, suggesting that forming long-term bonds is an important dominance strategy. However, the fact that male association patterns were sensitive to upheaval in the male dominance hierarchy suggests that males also take advantage of a changing social climate when choosing association partners. By contrast, the overall strength of female associations was relatively weak. Female association preferences were equally stable as males’; however, this reflected a dyad’s tendency to be found in the same party rather than to associate closely within that party. Therefore, in this community, female association patterns appear to be more a consequence of individual ranging behavior rather than a correlate of cooperation.


Association patterns Social bonds Cooperation Sex differences Alliance Chimpanzee 



Long-term research at Kanyawara was supported by funding from NSF Grant 0416125 to R. Wrangham. I. Gilby was also partially supported by NSF Grant IIS-0431141. We thank the Uganda National Council for Science and Technology, the Uganda Wildlife Authority, and the Makerere University Biological Field Station for permission to conduct research within Kibale National Park. This research complies with the current laws of Uganda. This project would not have been possible without the hard work and dedication of the field research team, especially Francis Mugurusi, Christopher Muruuli, Peter Tuhairwe, Christopher Katongole, and the late Donor Muhangyi and John Barwogeza, as well as field managers Michael Wilson, Martin Muller, Katherin Pieta, Carole Hooven, Kimberly Duffy, Alain Houle, and Emily Otali. Thanks also to Kate Burmon for tireless data entry, Randall Collura for assistance with the phylograms, and to David Watts, Zarin Machanda, Melissa Emery Thompson, Meg Crofoot, Kimberly Duffy, and two anonymous reviewers for comments on earlier versions of this manuscript.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  1. 1.Department of AnthropologyHarvard UniversityCambridgeUSA

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