Can chimpanzees and apes remember friends after 25 years? Johns Hopkins University study reveals surprisingly human-like social memory

Johns Hopkins University researchers have found that chimpanzees and bonobos can recognize former groupmates even after more than 25 years apart, with apes showing especially strong attention toward old friends and family members. The findings offer a remarkable look at the long-lasting social memories of our closest living relatives.

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Can an ape remember a friend it has not seen for decades?

A study from Johns Hopkins University suggests that chimpanzees and bonobos may be capable of exactly that. Researchers found that the apes recognized photographs of former groupmates they had not seen for years — and in some cases, for more than 26 years. The study, published in Proceedings of the National Academy of Sciences, documents the longest-lasting social memory recorded in a non-human animal.


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Chimpanzees recognized old friends after decades

The research team studied chimpanzees and bonobos at Edinburgh Zoo in Scotland, Planckendael Zoo in Belgium and Kumamoto Sanctuary in Japan.

Researchers collected photographs of former groupmates who had either moved away or died. The animals in the study had not seen these individuals for at least nine months, while the longest separation lasted 26 years.

The researchers also gathered information about the relationships the apes had previously shared, including whether their interactions had been positive or negative.

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Apes looked longer at familiar faces

To test their memories, researchers gave the animals juice while showing them two photographs side by side — one of a former groupmate and another of an unfamiliar ape. A non-invasive eye-tracking device recorded where the animals looked and for how long.

The results were striking. The apes spent significantly more time looking at former groupmates than strangers. Even more interestingly, they looked longer at photographs of individuals with whom they had shared more positive relationships.

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This suggests their memories may involve more than simply recognizing a familiar face. Christopher Krupenye, an assistant professor at Johns Hopkins University and senior author of the study, said: "Chimpanzees and bonobos recognize individuals even though they haven't seen them for multiple decades."

He added: "It suggests that this is more than just familiarity, that they're keeping track of aspects of the quality of these social relationships."

One bonobo remembered family after 26 years

The most remarkable case involved a bonobo named Louise. At the time of testing, Louise had not seen her sister Loretta or nephew Erin for more than 26 years. Despite the extraordinary length of the separation, she showed a strong preference for looking at photographs of both relatives during eight trials.

The researchers said this suggests great ape social memory may last for a substantial part of their lives. Chimpanzees and bonobos typically live for around 40 to 60 years.

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Could chimpanzees miss their old friends?

The study also raises a fascinating question: if apes can remember individuals for decades, can they miss them? Scientists say the research cannot establish that apes experience missing someone in the same way humans do.

Lead author Laura Lewis said: "The idea that they do remember others and therefore they may miss these individuals is really a powerful cognitive mechanism and something that's been thought of as uniquely human."

She cautioned that the study does not prove this happens, but said it raises the possibility.

The findings could also have implications for conservation. Since all great apes are endangered, researchers say separating animals from their social groups through poaching and deforestation could have serious consequences.

"This work clearly shows how fundamental and long lasting these relationships are. Disruption to those relationships is likely very damaging," Krupenye said.