When one chimpanzee starts putting a blade of grass in her ear, it's an oddity. When a whole bunch of them copy the behavior, it's enough to make scientists go "hmm."
The behavior in question first turned up at Chimfunshi Wildlife Orphanage, in Zambia. In 2010, a rescued chimpanzee named Julie started walking around with a long-stemmed blade of grass sticking out of her ear. Over the next year, seven more chimpanzees in Julie's 12-member group began mimicking the behavior.
A team of scientists from the Max Planck Institute for Evolutionary Anthropology, in Germany, documented the spread of this "spontaneously emerged tradition" (aka a fad), which they called "grass-in-ear behavior." According to a paper published in the current issue of the journal Animal Cognition, the blades of grass were left in during grooming, playing, and resting. Although the behavior spread to most of Julie's group, it did not spread to three other chimpanzee troops at the same sanctuary, with the exception of one chimp who tried it out a single time.
So why did they do it? As the authors write in their paper, "The behaviour served no discernible purpose." Lead author Edwin J.C. van Leeuwen was in the field and unable to respond to an interview request, but he told The Dodo last week that grass-in-ear behavior "is quite unique in the sense that nothing seems to be communicated by it."
Chimpanzee social learning has been well documented, but this represents something new, said Dr. Anne Pusey, director of the Jane Goodall Institute Research Center at Duke University, who was not affiliated with the study.
"Certainly the transmission of new behaviors has been observed before," she said, noting those are usually practical skills, such as food-gathering techniques. Most recently at Gombe Stream National Park, a unique behavior of using twigs to "fish" for carpenter ants in trees moved from one chimpanzee community to another after a female chimp switched groups.
Pusey said she was not surprised by the new grass-in-ear behavior but acknowledged that there are almost no studies of nonpractical behaviors like this spreading from one chimp to another. She said Goodall and others observed something similar at Gombe, where young chimps would flip down their lower lip so it covered their chins. "There was some suggestion at Gombe that this became a fashionable thing to do," Pusey said. That behavior has not yet been fully studied.
Chimps enjoy a little ornamentation from time to time. Chimps at Gombe have routinely stolen items of clothing and draped them over their shoulders. Some young female chimps have been observed carrying bits of wood as if they were dolls. "Young chimps, especially infant chimps, do put things on their head when they're playing," Pusey said. "But putting things in their ear—that's a bit different."
Will the grass-in-ear fad continue, will it spread to other groups, or will something else take its place? It's hard to say, but the paper shows that these apes are even more like humans than previously thought. As the authors write, "Chimpanzees have a tendency to copy each other's behavior, even when the adaptive value of the behavior is presumably absent."
Does that sound like anyone you know?