It’s not just humans – chimpanzees also like to follow trends, study shows

Chimpanzees living in a sanctuary in Africa have developed a “fashion trend” for dangling blades of grass or sticks from their ear holes and their behinds, a new study shows.

In 2010, researchers working at Chimfunshi Wildlife Orphanage Trust chimpanzee sanctuary in Zambia observed how a female chimp started to dangle objects from her ear, and the behavior was soon copied by other members of her group, study lead author Ed van Leeuwen, an assistant professor of behavioural biology at Utrecht University in the Netherlands, told CNN on Wednesday.

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.

The behavior is more of a “fashion trend or social tradition,” he added.

Aimi, a female chimpanzee, wearing a stick in her ear - Jake Brooker/Chimfunshi Wildlife Orphanage Trust

Interestingly, chimpanzees in a different group at the sanctuary started demonstrating the same behavior more than a decade later, with some also inserting objects into their rectums.

As this group lived around nine miles from the first group, they couldn’t have copied it from them, prompting Van Leeuwen to ask whether the chimpanzees’ caregivers could have influenced them.

As it turns out, the staff in one area of the reserve had developed a habit of cleaning their ears with matchsticks or twigs, while those on the other side didn’t.

Van Leeuwen believes the behavior was picked up by chimpanzees from caregivers in the first area, before it was passed on to other members of their group.

The caregivers then also influenced the behavior in the second group, which they were looking after years later, before this group also developed the practice of inserting sticks and grass into their rectums.

“This is a trend that goes viral by means of social learning,” he added.

An adult male chimpanzee exhibits the same behavior in a forested sanctuary for rescued great apes. - Jake Brooker/Chimfunshi Wildlife Orphanage Trust

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,” said Van Leeuwens.

Nonetheless, wild chimpanzees are probably capable of developing such behavior, he said, adding that it just might not have been documented yet.

Next, Van Leeuwens plans to study whether chimpanzees can repeatedly innovate new foraging techniques, to examine whether they can develop cumulative culture in the same way as humans.

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.

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