A study out of a chimpanzee sanctuary in Africa found that chimpanzees (Scientific name: Pan troglodytes) seemingly mirror somewhat meaningless behaviors in order to feel socially accepted. And dangling blades of grass or sticks from their ear holes and their behinds becomes trendy for some chimps, it would seem.
It's very similar to how fashions and trends emerge in humans. Dr Jake Brooker (right) from Durham University, said: "This isn't about cracking nuts or fishing for termites – it's more like chimpanzee fashion. It mirrors how human cultural fads spread: someone starts doing something, others copy it, and it becomes part of the group identity even if it serves no clear purpose".
It's not the first time this kind of behavior has been seen in chimpanzees at the Chimfunshi Wildlife Orphanage Trust sanctuary, which is located along the Chingola–Solwezi Road in Zambia.
The grass-in-ear fad was first documented in 2010, when a female chimpanzee named Julie was observed repeatedly inserting grass into her ear. Later, the idiosyncratic behavior would be adopted by seven other chimps in the same group, and persisted even after Julie’s death, “suggesting it had become a cultural tradition”, the study authors write. “Unlike most chimpanzee traditions that involve tool use or foraging, the grass-in-ear behavior more closely resembled human fashion trends, where the function may be less tangible than in the instrumental context of foraging”.
“This shows that, like humans, other animals also copy seemingly pointless behaviours from one another”, fellow researcher from Utrecht University and study lead author Edwin van Leeuwen
(left) explained. “And that, in turn, may offer insights into the evolutionary roots of human culture”.
There was no evidence that the chimpanzees were using the grass or sticks to deal with pain or itches, and they were “very relaxed” when they did it, Van Leeuwen said.
Fast forward some 15 years, and chimpanzees in another group at the same sanctuary have hopped on the bandwagon, despite having no contact with the original group. Five out of eight chimps were spotted wearing grass in their ears, while six put their own unique stamp on the trend, letting the blades dangle from their behinds.
Neither behavior was seen in any other group in the sanctuary, except for two males in the original grass-in-ear group. After tracking the animals for some time, the team noticed they were copying the behavior from each other, and may have identified the original trendsetter (plot twist: they’re not a chimp).
“Both groups where chimps put blades of grass in their ears, had the same caretakers. These caretakers reported that they sometimes put a blade of grass or a matchstick in their own ears to clean them”, Van Leeuwen said. “Caretakers in the other groups said they did not do this. The chimps in the one group then figured out to stick the blade of grass in another place as well”.
It’s impressive, especially considering that some scientists have been known to believe humans are unique in our ability to replicate seemingly pointless details. This new research challenges that assumption.
“This is a trend that goes viral by means of social learning”, Van Leeuwen reiterated.
Van Leeuwen also cited the example of a group of chimpanzees at a zoo in the Netherlands in which one female started walking as if she were carrying a baby even though she wasn’t.
Soon, all of the females had adopted this walking style, he said.
In addition, when two new females were brought into the group, the one that adopted the style swiftly was integrated quickly, whereas the one that refused to walk in the group style took longer to be accepted.
For Van Leeuwen, these behaviors are about fitting in and smoothing social relationships, just as with humans.
The grass behavior was mostly observed at leisure time, when the chimpanzees congregate to groom and play.
Living in the sanctuary, the chimpanzees don’t have to worry about predators or competition with other groups, meaning they have more leisure time than their wild counterparts. “They have a lot of time to just hang out”, argued Van Leeuwens.
Nonetheless, wild chimpanzees are probably capable of developing such behavior, he said, adding that it just might not have been documented yet.
Elodie Freymann, a post-doctoral affiliate at the University of Oxford’s Primate Models for Behavioural Evolution Lab, who was not involved in the study, told CNN that these kinds of observations are key to advancing our understanding of the origins and transmission patterns of cultural behaviors in chimpanzees and other non-human animals.
“This study’s finding that there may have been interspecies copying between chimps and their human caretakers is pretty mind blowing”, she said.
“If chimps can copy humans, could they be learning from and copying other non-human species as well? It’s an exciting moment in primatology”, Freymann added.
Note: The said study "Chimpanzees socially learn non-instrumental behaviour from conspecifics" is published on July 04, 2025 in the journal Behaviour.
