The study says monkeys may remember their old friends and family decades later

The study says monkeys may remember their old friends and family decades later

Louise lost contact with her sister, Loretta. Life just got in the way. After moving from California to Ohio, then another trip to Japan, it had been 26 years since she had seen her brother.

But recently, when Louise found a photo of Loretta, her eyes lingered on her features: her dark eyes. Her thin hair. Her big ears.

Louise is a bonobo, a primate that is one of humanity’s closest living relatives. In a study published Monday, researchers say they found that bonobos and chimpanzees view photos of old friends, Family members and group mates We seem to remember them.

The findings, published in the Proceedings of the National Academy of Sciences, amount to some of the longest memories ever recorded in the animal kingdom. This discovery suggests that humanity’s complex social networks have deep evolutionary roots, and that long-term memory is likely a trait possessed by the common ancestor of humans, chimpanzees and bonobos several million years ago.

The study “traveled back in time 7 million years ago into the mind of our common ancestor that we had together, in a way we’ve never done before,” said Brian Hare, a cognitive scientist at Duke University, who was not involved in the study.

Inside the monkey’s mind

To learn about the minds of monkeys, the researchers lured 26 chimpanzees and bonobos in zoos in Scotland and Belgium and in a monkey sanctuary in Japan to stand in front of a screen. Using straws mixed with fruit juice to keep their heads still and an infrared camera to track their eye movement, the team showed the animals a pair of side-by-side images for three seconds. The monkeys were not restrained during the experiment.

“It’s a very elegant and simple way to encourage them to keep their heads still,” said Laura Lewis, a postdoctoral fellow at UC Berkeley and lead author of the study.

One of the pictures was of a monkey they had previously lived with. The other was from a complete stranger.

On average, bonobos and chimpanzees who viewed both images looked at their old teammates about a quarter of a second longer than at the stranger. In one experiment, shown in the video below, Edith spent a little more time looking at photos of chimpanzees she once lived with.

Edith the chimpanzee’s eye movement was tracked when shown images of her former colleagues and the strange chimpanzee on 30 January 2019 at Edinburgh Zoo. (Video: Washington Post)

Christopher Krupeni, an assistant professor at Johns Hopkins University who co-wrote the study, likened the monkeys’ reaction to walking past an old high school classmate on the street.

“You might do a double take, and it might surprise you,” he said. “In a sense, our study is like that.”

Michael Platt, a professor at the University of Pennsylvania who has also conducted eye-tracking research, stopped short of saying that the experiment showed that bonobos and chimpanzees really recognized their old companions. Instead, he said the findings suggest the animals may have had a sense of familiarity with images of their old teammates.

“The authors interpret this difference to reflect face recognition,” said Platt, who was not involved in the latest study. “What the authors uncover appears to be evidence of familiarity.”

In studying, the amount of time Since the monkey lived with his old colleague It does not appear to affect the results. For example, the bonobo Louise last saw her sister at the San Diego Zoo in 1992 before she was transferred to the Cincinnati Zoo and then to the Kumamoto Reserve in Japan. When it comes to long-term memory, chimpanzees and bonobos join the ranks of humans and dolphins. Previous research has found that dolphins can remember each other’s whistles for more than two decades.

The bonobos and chimpanzees looked longer at old mates who had cared for them and had positive relationships with them in the past – longer, that is, as friends than enemies. Although whether animals are capable of friendship is up for debate.

“It’s sometimes called the f-word in primatology,” Lewis said. “But many of us now seem to agree that you can describe these positive, long-term relationships as friendships.”

For Krupeni, the results confirm what he and other humans who have been working with apes for years have experienced anecdotally.

“You get this distinct impression when we come back that it’s very clear that they recognize you.”

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