Facial width-to-height ratio in chimpanzees: Links to age, sex and personality

Citation

Wilson V, Weiss A, Lefevre CE, Ochiai T, Matsuzawa T, Inoue-Murayama M, Freeman H, Herrelko ES & Altschul D (2020) Facial width-to-height ratio in chimpanzees: Links to age, sex and personality. Evolution and Human Behavior, 41 (3), pp. 226-234. https://doi.org/10.1016/j.evolhumbehav.2020.03.001

Abstract
Links between the human facial width-to-height ratio (fWHR) and aggressive behaviours have been debated in recent years. The question of whether fWHR is a cue to dominance could benefit from the study of primate species that are closely related to humans. We therefore built on the broad literature in humans, and recent research in capuchins, macaques and bonobos, and examined associations between fWHR in 131 captive chimpanzees from the United States, United Kingdom and Japan, and measures of age, sex, subspecies (Pan troglodytes verus, P. t. schweinfurthii, P. t. troglodytes), and six personality components (Dominance, Extraversion, Conscientiousness, Agreeableness, Neuroticism, and Openness). We found no evidence for sexual dimorphism in fWHR, as has been found in humans. We did find a positive relationship between fWHR and Dominance in P. t. verus, but only in adult females. This finding contrasts with that in humans, where dominant males have wider faces. We discuss these results in light of male-female differences in temporal rank stability, and in contrast to findings for bonobos, providing a useful perspective for fWHR research in humans.

Keywords
Facial morphology; Pan troglodytes verus; Dominance; Sexual dimorphism; Social cues

Journal
Evolution and Human Behavior: Volume 41, Issue 3