Do apes miss their friends? New study unlocks secrets of ape social memory

By Stephen Beech via SWNS

Apes can remember friends they haven’t seen for more than 25 years, reveals new research.

The study recorded the longest-lasting non-human social memories ever documented.

Researchers found that apes recognize photos of groupmates they haven’t seen for more than 25 years - and respond even more enthusiastically to pictures of their friends.

The research team says their findings, published in the journal Proceedings of the National Academy of Sciences, underscore how human culture evolved from the common ancestors we share with apes, our closest relatives.

Study senior author Dr. Christopher Krupenye, of Johns Hopkins University, said: “Chimpanzees and bonobos recognize individuals even though they haven’t seen them for multiple decades.

“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.”

Lead author Dr. Laura Lewis, a biological anthropologist at the University of California, Berkeley added: “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.”

The research team was inspired to pursue the question of how long apes remember old pals through their own experiences working with primates - the sense that the animals recognized them when they’d visit, even if they’d been away for a long time.

Dr. Krupenye said: “You have the impression that they’re responding like they recognize you and that to them you’re really different from the average zoo guest.

“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?”

The researchers worked with chimps and bonobos at Edinburgh Zoo in Scotland, Planckendael Zoo in Belgium, and Kumamoto Sanctuary in Japan.

The team collected photographs of apes that had either left the zoos or died, individuals that participants hadn’t seen for at least nine months and in some cases for as long as 26 years.

The researchers also collected information about the relationships each participant had with former groupmates - if there had been positive or negative interactions between them, etc.

The team invited apes to participate in the experiment by offering them juice, and while they sipped it, the apes were shown two side-by-side photographs—apes they’d once known and total strangers.

Using a non-invasive eye-tracking device, the team measured where the apes looked and for how long, speculating they’d look longer at apes they recognized.

The apes looked "significantly" longer at former groupmates, no matter how long they’d been apart.

And they looked longer still at their former friends, those they’d had more positive interactions with.

In the most extreme case during the experiment, bonobo Louise had not seen her sister Loretta nor nephew Erin for more than 26 years at the time of testing.

She showed a "strikingly robust" looking bias toward both of them over eight trials.

The results suggest great ape social memory could last beyond 26 years, the majority of their 40- to 60-year average lifespan, and could be comparable to that of humans, which begins to decline after 15 years but can persist as long as 48 years after separation.

Such long-lasting social memory in both humans and our closest relatives suggests that this kind of memory was likely already present millions of years ago in our common evolutionary ancestors.

The researchers believe that memory likely forged a foundation for the evolution of human culture and enabled the emergence of uniquely human forms of interaction where relationships are maintained over years of separation.

Dr. Krupenye says the idea that apes remember information about the quality of their relationships is another new and human-like finding of the work.

Dr. Lewis said: “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."

The study also raises the question of whether the apes are missing individuals they’re no longer with, especially their friends and family.

Dr. 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.

“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 researchers hope their findings deepen people’s understanding of the great apes, all of which are endangered species while shedding new light on how deeply they could be affected when poaching and deforestation separate them from their mates.

Dr. Krupenye added: “This work clearly shows how fundamental and long-lasting these relationships are.

"Disruption to those relationships is likely very damaging."

The researchers now plan to explore whether long-lasting social memories are special to great apes or something experienced by other primates.