STUDY: Chimps and bonobos can recognize long-lost friends and family for decades

For bonobos and chimpanzees memory is essential to maintaining a complex web of social relationships . Researchers have long suspected that chimps and bonobos have a robust capacity for social memory just as humans do (our genomes are about 99% identical). The research study showed that chimps and bonobos may be able to remember each other for a very long time. The study was also able to document the longest memory recorded in a nonhuman animal, that of Louise, a bonobo at Kumamoto Sanctuary, at 26 years. Social memory beyond just a few years had previously been documented only in dolphins, which studies have found can recognize vocalizations for up to 20 years.

CORINNE PURTIL: For humans, memory is essential to maintaining our complex web of social relationships. We have to remember who is a friend and who is a foe; who can be counted on for loyalty and who royally screwed you over during the last struggle for dominance.

Bonobos and chimpanzees, our closest living relatives, maintain similar social dynamics. Like us, they live in what scientists call “fission-fusion” societies, meaning they frequently split up to collect food and other resources before joining up again.

We shared a common ancestor roughly 5 million to 7 million years ago, a heartbeat in evolutionary time. Our genomes are about 99% identical…

Given these similarities, researchers have long suspected that chimps and bonobos have a robust capacity for social memory just as humans do. But unlike battles between rivals or grooming behaviors among friends, it’s hard to observe the act of an ape’s remembering.

“They have long-lasting social relationships that are really important for their survival and well-being,” said Laura Simone Lewis, a biological anthropologist and comparative psychologist who is a postdoctoral fellow at UC Berkeley. “It would make sense that they then have capacities to foster and maintain these social relationships for decades as well. We think that one capacity that helps them with that is being able to remember individuals.”

Lewis, Krupenye and their colleagues set out to record evidence of social memory in nonhuman primates. They used the same tool scientists often employ as a proxy for attention in human studies: eye tracking. Sure enough, they found that the apes spent significantly more time studying images of former groupmates compared with photos of strangers.

When presented with a picture of an individual they had shared a positive relationship with, they lingered even longer. “Chimpanzees and bonobos were looking longer at the images of their previous groupmates with whom they had these more positive social relationships, or something like you might call their friends,” Lewis said”…

The authors expected the quality of the chimps’ and bonobos’ memories would degrade over time, but that wasn’t the case. The apes’ focus on former groupmates was equally intent if they had been separated for two years or 10. The study also documented the longest memory so far recorded in a nonhuman animal. Louise is a bonobo at Kumamoto Sanctuary who had been transferred there 26 years earlier from the San Diego Zoo…

Brian Hare, an evolutionary anthropologist at Duke University who was not involved with the study, stated “our shared ancestors with other apes undoubtedly had remarkable memory because we see here that other living ape relatives, like our own species, can remember for decades details about their social relationships”…

Other researchers said the findings resonated with their personal observations of ape behavior. “I am not surprised that the research indicated that bonobos and chimpanzees possess an enduring memory for previous social partners,” said Arizona State University anthropologist Kevin Langergraber,… “Some members of a group may not see each other for several weeks or months, perhaps even years,” Langergraber said. “But during reunification after these long separations, the individuals will treat each other as group members rather than as strangers”. SOURCE…

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