In a first, study finds apes recognize pals they haven't seen in decades

In what may put some of us to shame, apes instantly recognize family and friends that they haven’t seen in more than two decades, which is the longest ‘social memory’ in a non-human animal ever documented.

Offering key insights into how human social recognition evolved, the study from Johns Hopkins University came about after researchers noticed how the animals seemed to recognize humans they’d spent time with, even if it had been a long time between visits.

“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,” said lead author Laura Lewis, a biological anthropologist at the University of California, Berkeley (UCB). “And I think that is what's so exciting about this study."

Working with chimpanzees and bonobos at Edinburgh Zoo in Scotland, Planckendael Zoo in Belgium, and Kumamoto Sanctuary in Japan, the researchers prepared sets of photos that featured one familiar animal and one stranger. The apes were free to come and go from an area that had a juice feeder (sugar-free, as one researcher made a point of noting). A window above the juice nozzle displayed two images specific to each animal, with one photo of a member of the group who had either died or been moved to another enclosure, and another that the ape had never seen before. Their focus was then measured with a non-invasive eye-tracking device to determine if the animals did actually spend more time looking at ‘friends’ or family. And they did.

"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," said senior author Christopher Krupenye, an assistant professor and animal-cognition specialist at Johns Hopkins University. “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?"

What they found was that the apes spent significantly more time looking at animals that had formerly been part of their social group and they had positive associations with.

One ape, a bonobo named Louise, had not seen her sister Loretta and nephew Erin for 26 years, but over eight trials she consistently focused on their images compared to the unfamiliar animal.

These findings have excited the researchers, as given the common ancestor humans share with these animals, social memory appears to have been an important factor in the evolution of our species.

"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," Lewis said.

Naturally, this research also raised the question of whether these animals long for the apes they’ve been separated from, and how close that could be to a human experience.

"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," Lewis said. "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 now want to expand the study to include other primates, and to see if any nuances in eye contact can reveal more about the nature of past relationships. A better understanding of these complex connections can also help in managing the welfare of captive animals.

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

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

For more on the study, see this video below.

Source: Johns Hopkins University