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Coevolution of Facial Expression and Social Tolerance in Macaques


  • Contract grant sponsor: Dartmouth College Junior Faculty Fellowship.

*Correspondence to: Seth Dobson, Dartmouth College, HB 6047, Hanover, NH 03755. E-mail:


The purpose of this study is to test the hypothesis that social tolerance drives the evolution of facial expression in macaques. Macaque species exhibit a range of social styles that reflect a continuum of social tolerance. Social interactions in more tolerant taxa tend to be less constrained by rank and kinship than in less-tolerant macaques. I predicted that macaques that are more tolerant would exhibit a wider range of facial displays than less-tolerant species because interactions that are open to negotiation are characterized by greater uncertainty than interactions that are constrained by rank or kinship. To test this hypothesis, I conducted a phylogenetically informed regression analysis (N = 11) using previously published data on repertoire size and two quantitative measures of social tolerance (conciliatory tendency and counter-aggression). As predicted, macaques with more tolerant social styles tended to have larger repertoires than less-tolerant species. These results support the hypothesis that increased social tolerance favors the elaboration of communication to mitigate uncertainty.