Personality heterophily and friendship as drivers for successful cooperation

Debottam Bhattacharjee*, Sophie Waasdorp, Esmee Middelburg, Elisabeth H.M. Sterck, Jorg J.M. Massen

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Cooperation is widespread and arguably a pivotal evolutionary force in maintaining animal societies. Yet, proximately, what underlying motivators drive individuals to cooperate remains relatively unclear. Since 'free-riders' can exploit the benefits by cheating, selecting the right partner is paramount. Such decision rules need not be based on complex calculations and can be driven by cognitively less-demanding mechanisms, like social relationships (e.g. kinship, non-kin friendships, dyadic tolerance), social status (e.g. dominance hierarchies) and personalities (social and non-social traits); however, holistic evidence related to those mechanisms is scarce. Using the classical 'loose-string paradigm', we tested cooperative tendencies of a hierarchical primate, the long-tailed macaque (Macaca fascicularis). We studied three groups (n = 21) in their social settings, allowing partner choice. We supplemented cooperation with observational and experimental data on social relationships, dominance hierarchies and personality. Friendship and dissimilarities in non-social 'exploration' and 'activity-sociability' personality traits predicted the likelihood of cooperative dyad formation. Furthermore, the magnitude of cooperative success was positively associated with friendship, low rank-distance and dissimilarity in the activity-sociability trait. Kinship did not affect cooperation. While some findings align with prior studies, the evidence of (non-social) personality heterophily promoting cooperation may deepen our understanding of the proximate mechanisms and, broadly, the evolution of cooperation.

Original languageEnglish
Article number20232730
Number of pages11
JournalProceedings of the Royal Society B: Biological Sciences
Issue number2019
Publication statusPublished - 27 Mar 2024


  • cooperative decision rules
  • friendship
  • partner choice
  • personality heterogeneity
  • primates


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