Fifteen years ago in a sanctuary in Zambia, inspiration struck a chimpanzee named Julie. She plucked a stiff blade of grass, stuck it inside her ear, and left it there. There the grass dangled as Julie played, groomed, and rested. The behavior soon spread to most of the other chimpanzees in Julie’s group, called Group 4, and was adopted by her son Jack and chimps Kathy, Miracle, and Val. In the span of just one year, Julie was observed with grass in her ear 168 times; by comparison, the next most frequent observer was Kathy, with 36 grass-in-ear sightings. After Julie died in 2013, her invention lived on, with Kathy and Val carrying the torch.
The ear grass served no clear purpose, except, perhaps, fashion. But its quick spread and persistence even after Julie’s death suggests grass-in-ear had become a cultural tradition for this particular group at the Chimfunshi sanctuary for rescued chimps. Now, a different group of chimps at Chimfunshi have debuted a totally new grass-based innovation, all thanks to a chimp named Juma, who has invented grass-in-rear.
This behavior is pretty much what it sounds like: Juma inserts a stiff blade of grass into his rectum and lets it hang. When the researchers first noticed grass-in-rear, “we were quite confused,” said Jake Brooker, a primatologist at Durham University. Grass-in-rear, much like grass-in-ear, has no clear purpose. As such, a group of researchers including Brooker argue in a paper in Behaviourthat Juma’s invention is an example of a new social chimpanzee cultural tradition.
In 2023, the researchers had come to Chimfunshi for research totally unrelated to rectums. One of the authors, Alex Rogers, was tasked with following a single chimp around all day in Group 8, which includes Juma. Rogers soon realized the chimps had certain cultural norms, starting with a classic: grass in the ear. On Aug. 16, Juma stuck grass in his ear, followed by four more chimps that week.