Apes recognize long-lost friends after decades

A new study from John Hopkins University reveals that apes can recognize photographs of their groupmates, even after a separation of over 25 years. This discovery highlights the longest-lasting social memory documented outside of humans, offering profound insights into the evolution of human culture from our shared ancestry with apes.

“Chimpanzees and bonobos recognize individuals even though they haven’t seen them for multiple decades,” said study senior author Professor Christopher Krupenye.

“And then there’s this small but significant pattern of greater attention toward individuals with whom they had more positive relationships. It suggests that this is more than just familiarity, that they’re keeping track of aspects of the quality of these social relationships.”

Memory mechanisms of apes

Study lead author Laura Lewis is a biological anthropologist and comparative psychologist at the University of California, Berkeley. She reflected on the cognitive similarities between apes and humans.

“We tend to think about great apes as quite different from ourselves but we have really seen these animals as possessing cognitive mechanisms that are very similar to our own, including memory. And I think that is what’s so exciting about this study,” said Lewis.

The study was inspired by the researchers’ personal experiences with apes, noting their apparent recognition and enthusiastic responses after long absences. 

“You have the impression that apes are responding like they recognize you and that to them you’re really different from the average zoo guest,” said Krupenye. “They’re excited to see you again. So our goal with this study was to ask, empirically, if that’s the case: Do they really have a robust lasting memory for familiar social partners?”

How apes recognize their families

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

The apes were shown photographs of former groupmates – including some they had not seen for up to 26 years – alongside images of strangers.

The results were striking. The apes demonstrated a significant preference for looking at former groupmates over strangers, and even more so at friends. 

In a notable instance, bonobo Louise showed a strong bias towards her sister Loretta and nephew Erin, whom she hadn’t seen for over 26 years.

Social memory of apes

These findings suggest that great ape social memory could outlast the majority of their 40 to 60-year lifespan, comparable to human memory, which can persist as long as 48 years after separation. 

This longevity in memory might have been present in our common evolutionary ancestors and could have played a crucial role in the development of human culture, including maintaining long-term intergroup relationships.

The idea that apes remember information about the quality of their relationships, years beyond any potential functionality, is another novel and human-like finding of the work, said Krupenye.

“This pattern of social relationships shaping long-term memory in chimpanzees and bonobos is similar to what we see in humans, that our own social relationships also seem to shape our long-term memory of individuals,” said Lewis.

Study implications

The research raises intriguing questions about the emotional depth of apes. Do they miss their friends and family members they no longer see? 

“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,” said Lewis. “Our study doesn’t determine they are doing this, but it raises questions about the possibility that they may have the ability to do so.”

The team hopes the findings will improve our understanding of great apes while shedding new light on how deeply they could be affected when poaching and deforestation separate them from their groupmates.

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

Looking ahead, the research team aims to investigate whether this remarkable social memory is unique to great apes or shared by other primates. They also plan to explore the richness of ape memories, probing whether they can remember experiences as vividly as they remember individuals.

The study is published in the journal Proceedings of the National Academy of Sciences.

Video Credit: Johns Hopkins University

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