Abstract
Several recent studies show that animal friendships, like human friendships, are durable and have fitness benefits by increasing survival, infant survival, or reproductive success. However, the determinants of especially non-kin friendships are unclear. Human non-kin friendships are partly determined by similarity in personality. We investigated personality similarity of friends in 38 captive chimpanzees. Within-subject comparisons revealed that friends are more similar than non-friends in their Sociability and Boldness. Subsequent analyses, including both kin- and non-kin dyads, revealed higher similarity in Sociability among all individuals who sat in contact more often, while in Boldness and Grooming Equity the positive effect of similarity was only found in non-kin individuals' contact-sitting. Our results show that similar to humans, chimpanzees' friendships are related to homophily in certain personality characteristics, particularly those relevant for socio-positive and cooperative behaviour. We suggest that having friends similar to self in personality decreases uncertainty in interactions by promoting reliability especially in cooperative contexts, and is consequently adaptive. Further, we suggest that homophily in human friendships dates back at least to our last common ancestor with chimpanzees.
| Original language | English |
|---|---|
| Pages (from-to) | 1-8 |
| Number of pages | 8 |
| Journal | Evolution and Human Behavior |
| Volume | 35 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 1 Jan 2014 |
| Externally published | Yes |
Funding
We thank Burgers’ Zoo, Arnhem, and Dierenpark Amersfoort, the Netherlands, especially Tom de Jong, Wineke Schoo, Raymond van der Meer, and all the keepers for great enthusiasm and cooperation during the studies. We thank Thomas Bionda, Athena Vervloet, Anne-Marie Arnold, Sanja Antonides, Dorith Vermunt, and many earlier students in the Arnhem chimpanzee project of SEK for their help in collecting data. Carel van Schaik, Thomas Bugnyar, Wiebke Schuett, Alecia Carter, Daniel Hruschka and two anonymous reviewers are thanked for discussions and very helpful comments on the manuscript. Finally, we gratefully acknowledge our funding bodies: the Lucie Burgers Foundation (to JJMM), the Austrian Science Foundation FWF (grant-nr. M 1351-B17 to JJMM), and the Ella and Georg Ernrooth Foundation (to SEK).
Keywords
- Chimpanzees
- Cooperation
- Friendship
- Homophily principle
- Personality