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The evolutionary drivers of primate scleral coloration

Mearing, Alex S.; Burkart, Judith M.; Dunn, Jacob; Street, Sally E.; Koops, Kathelijne

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Authors

Alex S. Mearing

Judith M. Burkart

Jacob Dunn

Kathelijne Koops



Abstract

The drivers of divergent scleral morphologies in primates are currently unclear, though white sclerae are often assumed to underlie human hyper-cooperative behaviours. Humans are unusual in possessing depigmented sclerae whereas many other extant primates, including the closely-related chimpanzee, possess dark scleral pigment. Here, we use phylogenetic generalized least squares (PGLS) analyses with previously generated species-level scores of proactive prosociality, social tolerance (both n = 15 primate species), and conspecific lethal aggression (n = 108 primate species) to provide the first quantitative, comparative test of three existing hypotheses. The ‘self-domestication’ and ‘cooperative eye’ explanations predict white sclerae to be associated with cooperative, rather than competitive, environments. The ‘gaze camouflage’ hypothesis predicts that dark scleral pigment functions as gaze direction camouflage in competitive social environments. Notably, the experimental evidence that non-human primates draw social information from conspecific eye movements is unclear, with the latter two hypotheses having recently been challenged. Here, we show that white sclerae in primates are associated with increased cooperative behaviours whereas dark sclerae are associated with reduced cooperative behaviours and increased conspecific lethal violence. These results are consistent with all three hypotheses of scleral evolution, suggesting that primate scleral morphologies evolve in relation to variation in social environment.

Citation

Mearing, A. S., Burkart, J. M., Dunn, J., Street, S. E., & Koops, K. (2022). The evolutionary drivers of primate scleral coloration. Scientific Reports, 12, Article 14119. https://doi.org/10.1038/s41598-022-18275-9

Journal Article Type Article
Acceptance Date Aug 8, 2022
Online Publication Date Aug 18, 2022
Publication Date 2022
Deposit Date Sep 15, 2022
Publicly Available Date Sep 15, 2022
Journal Scientific Reports
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 12
Article Number 14119
DOI https://doi.org/10.1038/s41598-022-18275-9

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http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Advance online version This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.





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