Monkeys remember friends they haven’t seen for decades

A new study reveals that monkeys recognize photos of groupmates they haven’t seen in more than 25 years and respond more enthusiastically to photos of their friends, according to the authors of the study published in the journal Proceedings of the National Academy of Sciences.

This work demonstrates the most enduring social memory ever documented outside of humans, and highlights how human culture evolved from the common ancestors we share with apes, our closest relatives.

“Chimpanzees and bonobos recognize individuals even if they haven’t seen them for decades,” said Christopher Kropini, lead author and associate professor at Johns Hopkins University who studies animal cognition. In addition, there was a small but significant pattern of greater interest in individuals with whom they had more positive relationships. This suggests that it is more than just familiarity, but that they are monitoring the quality of these social relationships.

“We tend to think that great apes are very different from us, but in fact we have seen that these animals have cognitive mechanisms that are very similar to our own,” adds lead author Laura Lewis, a biological anthropologist and comparative psychologist at the University of California, Berkeley. us.ours, including memory. I think that’s what’s interesting about this study.

The research team was inspired to investigate how long monkeys remember their fellow humans by their own experiences working with monkeys: the feeling that animals recognized them when they visited, even if they had been away for a long time.

“You get the impression that they’re responding as if they’re getting to know you, and that to them you’re really different from the average zoo guest,” Krupeni says. They are excited to see you again. Our goal with this study was to experimentally test whether this is the case: Do they really have a strong lasting memory of their familiar social partners?

I studied monkeys

The team worked with chimpanzees and bonobos at Edinburgh Zoo (Scotland), Blankendael Zoo (Belgium), and Kumamoto Reserve (Japan). The researchers collected photographs of apes that had left zoos or died, individuals that participants had not seen for at least nine months and, in some cases, for up to 26 years.

The researchers also collected information about the relationships each participant maintained with their former group mates: whether there were positive or negative interactions between them, and so on.

The team invited the monkeys to participate in the experiment by offering them juice, and as they sipped it, they were shown two pictures side-by-side: of monkeys they had met and one they had never met before. Using a non-invasive eye-tracking device, the team measured where the monkeys looked and for how long, anticipating that they would look longer at the monkeys they recognized.

The monkeys looked longer at their former group mates, regardless of how long they had spent apart from each other, and they looked longer at their former friends, with whom they had had more positive interactions.

In the most extreme case of the experiment, the bonobo Louise had not seen her sister Loretta or her nephew Erin for more than 26 years at the time of the tests. He showed a surprisingly strong gaze bias toward both across eight experiments.

The results suggest that great apes’ social memory can last for more than 26 years, most of their average lifespan of 40 to 60 years, and is comparable to social memory in humans, which begins to decline at age 15. But it can last until the age of 15 years. After 48 years of separation.

Such long-term social memory, both in humans and our closest relatives, suggests that this type of memory may have already existed millions of years ago in our common evolutionary ancestors.

According to the authors, this memory likely laid the foundations for the evolution of human culture and allowed the emergence of exclusively human forms of interaction, such as intergroup trade, where relationships are maintained over many years of separation.

The idea that monkeys remember information about the quality of their relationships that extends beyond the years of any potential job is another new discovery that is unique to humans at work, Krupeni stresses.

“This pattern of social relationships that determines long-term memory in chimpanzees and bonobos is similar to what we see in humans: it appears that our social relationships also determine our individual long-term memory,” Lewis says.

Memory and feelings

This work also raises the question of whether monkeys miss individuals they are no longer with, especially their friends and family.

“The idea that they remember others, and therefore might miss them, is a very powerful cognitive mechanism and something that is uniquely human,” Lewis says. “Our study does not determine that they do, but it raises questions about the possibility that they have the ability to do so.”

The team hopes the findings will deepen people’s knowledge of great apes, and all threatened species, while shedding new light on how deeply they are affected when poaching and deforestation separate them from their fellow species.

“This work clearly shows how important and long-lasting these relationships are. A break in these relationships can be extremely harmful,” Krupeni warns.

The team wants to know whether these long-term social memories are limited to great apes or exist in other primates. They also want to know how rich the monkeys’ memories are, and whether, for example, they have long-term memories of both experiences and individuals.