Study: Chimpanzees recognize photos of friends they haven't seen for decades

Three female chimpanzees nod-off as they sit on rocks in a family group. (Credit: ROB ELLIOTT/AFP via Getty Images)

A new study has presented evidence that chimpanzees recognize familiar faces, even after years of separation. 

Researchers tested 26 apes from three locations,  Scotland, Japan and Belgium, using an eye-tracking task examining memory specific to faces.

"We study apes at zoos and sanctuaries around the world, often working with them for weeks or months at a time," Christopher Krupenye, an assistant professor of psychological and brain sciences at Johns Hopkins University and a co-author of this study told FOX Television Stations. "In some cases, it can be years until we return, and yet we always have the distinct impression that they remember us. They often come over and attempt to interact with us, rather than ignoring us as they do for most zoo visitors. Our goal was to see whether we could carefully design a study to show empirically that apes indeed remember familiar social partners for years."

In the study, the team presented chimpanzees and bonobos with side-by-side images of a previous groupmate and a stranger of the same sex.

The researchers found that the apes’ attention was biased toward the former groupmate, indicating long-term memory for past social partners.

The results suggested that an ape’s recognition may persist for at least 26 years beyond separation.

"We are excited to be able to demonstrate long-term social memory in apes, consistent with some past work, but what we found surprising was how long they remembered past groupmates – at least 26 years or a majority of their lifetimes," Krupenye continued. 

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The team also found significant, but weak, evidence that, like humans, apes may remember the quality or content of these past relationships. They found apes’ looked longer toward individuals with whom they had more positive histories or social interaction.

"Social relationships are deeply important for apes and, in some sense, clearly continue in their minds beyond the present," Krupenye said, adding, "This work underscores the importance of conserving our highly endangered ape relatives –  both for their own right and, selfishly, so that we can continue to discover our own unique place in the natural world." 

Krupenye said his team hopes to do further research into whether, upon seeing a photo of a former groupmates, apes just recognize these individuals or whether they also begin to replay past interactions in their minds. 

This story was reported from Los Angeles.