Trending Chimps 

Fifteen years ago, researchers observing chimps in a sanctuary in Zambia noticed that a female chimp had taken on a new habit: She began sticking a blade of grass in her ear, leaving it there for no apparent reason.  

Soon after, seven members of the group copied that behavior, which remained in fashion even after the female trendsetter died.  

Now, researchers have published a study based on observations from more than a decade later, in which they document how chimps from another group at the same sanctuary also stuck blades of grass in their ears, even though they had no contact with the original group. 

Meanwhile, the newly observed group took the trend one step further: Five of the eight chimpanzees stuck grass in their ears, while six of the eight also had a blade of grass dangling from their rears. The trend was not observed in other chimp groups at the same sanctuary, despite similar living conditions. 

“Why they do exactly this particular thing, I’m not really concerned about,” study author Edwin van Leeuwen said in a statement. “But they’re copying the behavior from each other, that is the important insight.” 

By tracking which animals showcased the behavior over time and tracing it back to when it started, the researchers found that it was likely that the animals copied the behavior from their caretakers rather than inventing it themselves. 

“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,” said Van Leeuwen. “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.” 

Similar trends with no apparent purpose have been observed in chimps in captivity, but not in the wild. 

“In captivity, they have more free time than in the wild,” said Van Leeuwen. “They don’t have to stay as alert or spend as much time searching for food.” 

However, the researchers doubt that the trend is truly “useless.”

“It could also serve a social purpose,” said Van Leeuwen. “By copying someone else’s behavior, you show that you notice and maybe even like that individual. It might help strengthen social bonds and create a sense of belonging within the group, just like it does in humans.”