Chimpanzee Culture: From Grass in the Ear to a Novel Rear Innovation
A groundbreaking study reveals that chimpanzees are not only capable of cultural traditions, but are also inventing new ones – with one group at the Chimfunshi sanctuary in Zambia taking the trend to a surprising new place. Researchers have documented the spread of “grass-in-ear” behavior, initially sparked by a chimpanzee named Julie fifteen years ago, and now a new, related practice dubbed “grass-in-rear” pioneered by a chimp named Juma.
The Origins of a Trend: Grass in the Ear
In 2009, at the Chimfunshi Wildlife Orphanage in Zambia, a chimpanzee named Julie began a peculiar habit. She would pluck a blade of grass and insert it into her ear, leaving it dangling as she went about her day. This behavior quickly spread throughout her group, known as Group 4, and was adopted by her son, Jack, and other chimps including Kathy, Miracle, and Val. Within a year, Julie was observed with grass in her ear a remarkable 168 times – far surpassing the next most frequent practitioner, Kathy, who was observed 36 times.
Even after Julie’s death in 2013, the practice persisted, carried on by Kathy and Val, demonstrating the behavior had become a cultural tradition within the group. The purpose of this “ear grass” remained unclear, with researchers suggesting it might simply be a form of fashion.
A New Variation Emerges: Grass in the Rear
Now, a different group of chimpanzees at Chimfunshi, Group 8, has taken the concept a step further. Thanks to Juma, they’ve debuted a new innovation: inserting a blade of grass into their rectum and letting it hang. “When we first noticed grass-in-rear, we were quite confused,” admitted Jake Brooker, a primatologist at Durham University.
Like its predecessor, “grass-in-rear” appears to serve no practical purpose. However, Brooker and his team argue in a recent paper published in Behaviour that Juma’s invention represents a new social and cultural tradition. The researchers initially arrived at Chimfunshi in 2023 for unrelated research, but quickly noticed the unique behaviors within Group 8.
Observing the Spread of a Peculiar Practice
Alex Rogers, one of the researchers, began following Juma closely in August 2023. He observed Juma first placing grass in his ear on August 16th, followed by four other chimps that week. Then, on August 27th, Juma initiated the “unprecedented variation” of inserting the grass into his rectum.
Initial concerns about potential irritation or infection were quickly dismissed after a thorough checkup of Juma and the other chimps revealed no medical issues. The researchers then dedicated a month to meticulously documenting the spread of this unusual behavior. Juma’s influence was immediate; another chimp, Commando, adopted the practice on the same day. Within the week, Aimi, Congo, and Victoria followed suit, with John joining in a few months later.
Social Learning and the Power of Influence
While Juma appears to be the most dedicated practitioner of “grass-in-rear,” with other chimps showing less enthusiasm, the spread of the behavior highlights the importance of social learning within the group. “I do get the impression from the other chimps that they don’t like it very much,” Brooker noted. “They are maybe influenced and interested in trying it, but they don’t do it nearly as much as Juma does.”
Group 8 is comprised of chimps rescued from the bushmeat trade or born in the sanctuary, fostering a close-knit and tolerant community. This strong social bond likely facilitated the spread of Juma’s invention, particularly given his status as the second-highest ranked chimp in the group. Dominance, as demonstrated by Julie’s initial influence with “grass-in-ear,” often correlates with increased social influence and tolerance for novel behaviors.
The close relationship between Juma and Commando, who share a sleeping space, also played a role in the initial spread, with Commando then potentially influencing the female chimps within the group.
Beyond Humans: Recognizing Culture in the Animal Kingdom
This discovery adds to a growing body of evidence challenging the long-held belief that culture is uniquely human. Researchers have observed cultural traditions in other species, such as orcas wearing “salmon hats” and monkeys washing sandy sweet potatoes. “I’m very suspicious that these kind of arbitrary social trends do exist in many animals, and we just overlook them,” Brooker stated.
The arbitrary nature of these traditions suggests they may serve a crucial purpose in bolstering social identity and cohesion, fostering trust, familiarity, and cooperation within the group. The researchers hypothesize that the chimps in Group 8 may have initially learned to put grass in their ears by observing their human caretakers cleaning their ears with matchsticks.
The Importance of Protecting Animal Cultures
Conservation efforts often focus on habitat preservation, but Brooker emphasizes the importance of protecting animal cultures as well. These traditions can endure across generations and within families. Julie, the originator of “grass-in-ear,” passed away after giving birth to her son, Jewel. Remarkably, Jewel, unaware of his mother’s pioneering role, continues the practice as of 2025, demonstrating the enduring power of cultural transmission. “Jewel obviously has no idea that his mum was the one who invented his behavior, but he’s carrying on her invention,” Brooker said, “And I find that really touching.”
