Iris and sclera coloration in great apes

Researchers compared how gray-scale values of sclerae contrasted with iris coloration in 51 bonobos, 50 chimpanzees, and 52 humans, and found that sclerae are lighter than irises in bonobos and humans, whereas in chimpanzees sclerae are darker than irises, suggesting that some nonhuman great apes may also use gaze as a social cue, given that the relative contrast between the irises and sclerae among all three species was comparable, according to the authors.

Article #19-11410: “Scleral pigmentation leads to conspicuous, not cryptic, eye morphology in chimpanzees,” by Juan Olvido Perea-García, Mariska E. Kret, Antónia Monteiro, and Catherine Hobaiter.

MEDIA CONTACT: Juan Olvido Perea-García, National University of Singapore, SINGAPORE; tel: +65-8748 5910; email:

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