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Bared-teeth displays in bonobos (Pan paniscus): An assessment of the power asymmetry hypothesis

Vlaeyen, Jolinde M.R.; Heesen, Raphaela; Kret, Mariska E.; Clay, Zanna; Bionda, Thomas; Kim, Yena

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Jolinde M.R. Vlaeyen

Raphaela Heesen

Mariska E. Kret

Thomas Bionda

Yena Kim


Facial expressions are key to navigating social group life. The Power Asymmetry Hypothesis of Motivational Emancipation predicts that the type of social organization shapes the meaning of communicative displays in relation to an individual's dominance rank. The bared-teeth (BT) display represents one of the most widely observed communicative signals across primate species. Studies in macaques indicate that the BT display in despotic species is often performed unidirectionally, from low- to high-ranking individuals (signaling submission), whereas the BT display in egalitarian species is usually produced irrespective of dominance (mainly signaling affiliation and appeasement). Despite its widespread presence, research connecting BT displays to the power asymmetry hypothesis outside the Macaca genus remains scarce. To extend this knowledge, we investigated the production of BT in relation to social dominance in dyadic interactions (N = 11,377 events) of 11 captive bonobos (Pan paniscus). Although adult bonobos were more despotic than previously suggested in the literature, BT displays were produced irrespective of dominance rank. Moreover, while adults produced the BT exclusively during socio-sexual interactions, especially during periods of social tension, immature bonobos produced the BT in a wider number of contexts. As such, the results indicate that the communicative meaning of the BT display is consistent with signaling appeasement, especially in periods of social tension. Moreover, the BT display does not seem to signal social status, supporting the prediction for species with a high degree of social tolerance. These results advance our understanding of the origins of communicative signals and their relation to species' social systems.


Vlaeyen, J. M., Heesen, R., Kret, M. E., Clay, Z., Bionda, T., & Kim, Y. (2022). Bared-teeth displays in bonobos (Pan paniscus): An assessment of the power asymmetry hypothesis. American Journal of Primatology, 84(9), Article e23419.

Journal Article Type Article
Acceptance Date Jun 26, 2022
Online Publication Date Jul 18, 2022
Publication Date 2022-09
Deposit Date Jul 27, 2022
Publicly Available Date Feb 9, 2023
Journal American Journal of Primatology
Print ISSN 0275-2565
Electronic ISSN 1098-2345
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 84
Issue 9
Article Number e23419


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Copyright Statement
&copy; 2022 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.<br /> <br /> This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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