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+--- Thread: Article Are humans the only primates with white eyes? Why is that? (/thread-20032.html)
Are humans the only primates with white eyes? Why is that? - C C - Mar 23, 2026
https://www.forbes.com/sites/scotttravers/2026/03/22/why-are-humans-the-only-primates-with-white-eyes-an-evolutionary-biologist-explains/
INTRO: If you were to make eye contact with a chimpanzee, you’d likely notice something uncanny about them very quickly: you cannot easily tell where they’re looking. The tissue that surrounds their iris, known as the sclera, is dark brown or nearly black, which makes their gaze almost impossible to track.
Contrastingly, if you were to make eye contact with a friend or family member, you’d have no trouble instantly discerning the direction of their attention. Because human sclerae are bright white, our gaze is involuntarily legible; others can always tell, within a fraction of a second, exactly what we are focused on.
This, evolutionary biologists argue, is the product of hundreds of thousands of years of natural selection, which has sculpted the human eye into a highly precise social signaling instrument. Because of this selection, we are the only primates on Earth with uniformly white sclera. The larger question scientists have spent decades wrestling with is why.
The leading explanation for this unique exception comes from a theory known as the Cooperative Eye Hypothesis.
The hypothesis was initially formalized by Michael Tomasello and colleagues at the Max Planck Institute for Evolutionary Anthropology. Broadly, it proposes that human white sclera evolved specifically to make gaze direction visible to other humans. In turn, this would have enabled the kind of tight, wordless coordination that underpins almost all of our important social interactions, from raising children communally to building cities... (MORE - details)
RE: Are humans the only primates with white eyes? Why is that? - Magical Realist - Mar 26, 2026
The eyes betray what the lips are hiding. Seeing the eyes of someone diverted while you are talking to them is a sign they aren't listening anymore. Making eye contact is important in social encounters usually. Making eye contact with a young Latino male is taken as an insult. Rolling your eyes expresses exasperation. Prolonged staring at one thing usually indicates that one is thinking, except when it is a TV. Looking at a woman's breasts while she's talking to you is an instant insult. A quick diverting of one's gaze at someone while one is talking about someone is a secret clue of who you are referring to. Looking up indicates thinking about something. Looking down expresses sadness or solemnity. There is a whole language of eye movement going on between humans all the time.