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There’s old what’s-his-butt: Chimps recognize rear ends like humans recall faces

Scientists at the Leiden University in the Netherlands have discovered that chimps can recognize each other by their butts the way humans recall faces.
Scientists at the Leiden University in the Netherlands have discovered that chimps can recognize each other by their butts the way humans recall faces. AP file photo

So you pride yourself on never forgetting a face?

Well, chimpanzees can do you one better.

Scientists at Leiden University in the Netherlands have discovered that chimps can recognize one another by their butts the way humans recall faces.

They detail their findings in a study called “Getting to the Bottom of Face Processing.”

“For chimpanzees, it’s all about the butt,” notes The Verge. “You won’t find a female chimp going ‘My eyes are up here,’ as it turns out that chimps often tell each other apart based on their behinds. Their brains even process butts in the same way that we process faces.”

Social animals need to be able to recognize one another quickly, and not just for identity. Humans faces communicate attractiveness and health.

Chimp buttocks supply the same type of information — as in whether a rear they see belongs to a relative or a female who is ovulating, according to LiveScience.

“Faces are enormously important for people, and all the features of our faces are optimally arranged to be seen and to communicate,” study author Mariska Kret, a neuropsychologist at Leiden University, said in a statement.

“In the course of evolution, our faces have acquired more contrast: red lips, the whites of our eyes, eyebrows and a smooth skin that makes everything more visible.”

For their experiment — which took place at a primate institute in Japan where Kret worked for nearly a year — researchers had both humans and chimpanzees match photos of various body parts — faces, butts, feet — and compared how they did.

“For example, you’d see a picture of someone’s foot and then later some other photos, and then would be asked to pick if that was the one you saw,” The Verge explained. “Some of these images were right-side-up, some were inverted. Then, they got chimps to do the same thing.

“Humans, as predicted, had the inversion effect for faces but not for butts. The chimps, on the other hand, had more trouble matching butt pictures when they were upside-down, but not face photos.”

Researchers determined that for the chimps, butts had “priority over other categories of objects,” Kret said.

Color also played an important role for the chimps, she explained in the online study.

“It is not without reason that it’s the face and buttocks of female primates that are free of hair, which makes the skin and color all the more visible,” she said.

“Primates’ eyes are perfectly set to distinguishing red tints. That’s why not only emotional expressions, such as blushing when we are angry or shy, become more visible, but also sexual arousal. It also explains why the buttocks of female chimpanzees are red.

“That may not apply to humans, but it does explain why women use lipstick and blusher.”

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