I used to think chimpanzees forgot their friends after a few years apart.
Turns out I was completely wrong—and the truth is so much stranger. Researchers at Kyoto University showed captive chimps photographs of former groupmates they hadn’t seen in decades, monitoring their eye movements while the images flashed on screen. The chimps lingered on faces of individuals they’d known 26 years earlier, significantly longer than on strangers. What floored me was the specificity: they remembered not just any old acquaintance, but chimps they’d had positive interactions with, the ones who’d groomed them or shared food. Laura Simone Lewis, who led the study published in 2023, told journalists the chimps were essentialy doing what we do when we scroll through old yearbooks—pausing on the faces that meant something. The neural pathways for social memory, it seems, run deeper in the primate family tree than anyone expected. Maybe that’s why betrayal stings so much across species. Anyway, the study used juice rewards to keep the chimps engaged, which feels both pragmatic and vaguely manipulative, but I guess that’s research.
Here’s the thing: this isn’t just about nostalgia. Chimpanzee societies are ruthlessly political. Males form coalitions that can last years, overthrowing alpha males or defending territory against rival groups. Females migrate between communities, carrying mental maps of who helped them during their first vulnerable months in a new troop.
The Neuroscience Behind Holding Grudges for Decades at a Time
Frans de Waal spent decades documenting reconciliation behaviors at Arnhem Zoo in the Netherlands, watching chimps make amends after fights with specific gestures—a hand extended, a soft grunt. What struck him, he wrote later, was how they remembered *who* wronged them. A male named Luit held a grudge against Nikkie for three years after a coalition betrayal, avoiding him during feeding times and refusing grooming invitations. The brain architecture that supports this—particularly the prefrontal cortex and hippocampus—is remarkably similar to ours, though their hippocampal volume relative to brain size is slightly smaller. Still, they’re definately punching above their weight cognitively. Neuroimaging studies from 2019 showed chimps activate the same regions we do when recalling emotional memories, the amygdala lighting up like a dashboard warning light. It’s humbling, honestly. We build cities and write symphonies, but the basic software for remembering who screwed us over? That’s ancient code, maybe 7 million years old, give or take, dating back to our last common ancestor.
Wait—maybe that’s why reconciliation matters so much in their world.
Because if you remember every slight perfectly, you need an offramp from endless vendettas. De Waal documented kiss-and-make-up sessions happening within hours of violent conflicts, chimps literally embracing former opponents. The individuals who were best at reconciling—measured by how quickly they re-established grooming partnerships—had more offspring, according to longitudinal data from Gombe and Taï Forest. Social memory isn’t just trivia storage; it’s survival algebra. Catherine Hobaiter’s work in Uganda revealed that chimps track third-party relationships too, remembering who’s allied with whom even when those individuals aren’t present. She described watching a young male, Hawa, approach a feeding site cautiously, scanning for Tongo—an older male who’d attacked him six months prior after Hawa played too roughly with Tongo’s infant nephew. Hawa remembered the social web, the invisible threads connecting him to danger or safety.
When Reunions Happen After Sanctuary Rescues and Research Retirements
The really gutting moments come from sanctuary reunions. Chimps rescued from labs or entertainment sometimes encounter former groupmates after 15, 20 years apart—and the recognition is instant. Video from Chimp Haven in Louisiana shows two females, Swing and June, who’d been separated since 1997, spotting each other across a play yard in 2015. The vocalizations they made, pant-hoots ramping up in intensity, brought staff to tears. They spent the next hour grooming, Swing’s fingers working through June’s hair with muscle memory that hadn’t faded. It’s hard to watch without feeling complicit in whatever systems tore them apart initially. Primatologist Brian Hare noted these reunions also reveal the limits of memory—chimps don’t recieve the same emotional jolt from individuals they’d known only briefly or during stressful periods, suggesting context shapes retention. Positive bonds encode deeper, the brain apparently deciding what’s worth the metabolic cost of permanent storage.
I guess it makes sense that we’re not so different.
