Side-Eye May Be More Common Among Primates Than We Realized

Humans aren’t the only primates with white eyes, and chimps may use them for communication too.

RACHAEL FUNNELL
Digital Content Producer

Jan 30, 2023 9:36 AM



White eyes among chimpanzees might not be as rare as we once thought. Image credit: Lileluba, CC BY-SA 4.0, via Wikimedia Commons

The sclera isn’t something you tend to think of when imagining animals, but looking at a photo of a chimpanzee with white eyes you might get the feeling that something’s slightly off. This is because most primates have a dark sclera, which in human eyes is the white that surrounds the iris and pupil.

The evolution of a white sclera was thought to perhaps be tied to communication, as humans have an impressive ability to tell a lot from a simple look. Side eye? They’re not happy. Avoiding gaze? Something’s wrong. Rolling upwards? Why I oughta…

But what about our closest relatives? After all, we’re well aware that chimps and bonobos have remarkably complex social groups and communicate through all sorts of gestures (humans can translate half of them – see if you can in this online game). It was once thought that a white sclera was unique to humans, but it’s perhaps unsurprising that we’re increasingly realizing that isn’t actually the case.

Early cases of wild chimpanzees with white sclerae were thought to be anomalies caused by some kind of illness or mutation. However, a new review has found that eye color was highly variable in a large group of wild chimpanzees at Ngogo in Kibale National Park, Uganda. Of 230 individuals, 34 had white sclerae, and for five of these this was visible even when the animals were looking straight ahead. For the other 29, it was only noticeable if they looked left to right.

More:
https://www.iflscience.com/side-eye-may-be-more-common-among-primates-than-we-realized-67312