A pointless fashion trend or something else? Chimpanzees wear blades of grass in their ears and rears

A team of researchers from the University of Utrecht, the University of Durham and other institutions observed something remarkable in a chimpanzee sanctuary in Zambia. Several chimpanzees of a particular group have been seen hanging grass from their ear holes or manages, for no apparent reason. The behavior was not observed in other groups of chimpanzees in the same sanctuary, despite similar living conditions.

“This shows that like humans, other animals also copy behaviors apparently useless from each other,” explains Edwin Van Leeuwen, researcher at the University of Utrecht. “And this, in turn, can offer information on the evolutionary roots of human culture.”

An article on these results appears in Behavior.

People regularly do arbitrary things that seem to have immediate use, like shaving a line in their eyebrow or putting a fashionable scarf on themselves or their dog. Most people do not find these things themselves, but copy others.

Other animals also adopt behaviors from each other. Often, however, it is useful behavior, like chimpanzees learning from each other how to find food. But sometimes animals develop habits that do not seem to serve as a clear goal. For example, a fashion trend among the orcas, which was seen carrying a dead salmon on the head, attracted a lot of media attention last year. However, these types of “unnecessary” trends in animals have rarely been studied systematically.

Ears

In 2010, Van Leeuwen discovered that a female chimpanzee in the sanctuary of the orphanage of the chimfunshi fauna for several times stuck a blade of grass in the ear and left it there, for no apparent reason. Later, seven of the members of his group adopted behavior. And even after the death of the female pioneer, the behavior continued and some chimpanzees of the group still do it today. Van Leeuwen and his colleagues therefore interpreted this behavior as a cultural tradition.

More than a decade later, the chimpanzees in another group of the same sanctuary also began to stick grass blades in their ears. They did not copy this behavior of the previous group because they had no contact with them. But in the new group, the trend of the orb grass did not stop there. While five of the eight chimpanzees in the new group have covered grass in their ears, six of the eight also left a grass blade swinging from behind.

The researchers found no evidence that the chimpanzees were disturbed by their ears or gray and used grass blades, for example, to relieve itching.

Copy of caregivers

By carefully following which animals presented the behavior over time, Van Leeuwen and his colleagues showed that it was likely that animals do not each invent the behavior, but copied them from each other. When the researchers deepened how the behavior started, they found something striking.

“The two groups, where chimpanzees put grass blades in their ears, had the same guards. These guards reported that they sometimes put a grass blade or a match in their own ears to clean them,” said Van Leeuwen. “The guards in the other groups said they had not done so. The chimpanzees in a group then understood how to stick the grass blade in another place.”

In the wild, similar “useless” trends have not been seen in the chimpanzees. So why do they do so in captivity?

“In captivity, they have more free time than in wilderness. They do not have to remain as alert or spend as much time looking for food,” explains Van Leeuwen. “Why do they do this special thing exactly, I am not really concerned. But they copy the behavior of each other, it is important insight.”

Human culture

The question of why humans are more culturally evolved than other animals are always debated by scientists. Some scientists believe that the key lies in the unique capacity of humans to copy, including apparently useless details. Other animals would not be able to do so and should constantly reinvent the wheel, which limits their cultural evolution.

“But our study shows that chimpanzees are capable of copying small unnecessary behaviors from each other,” said Jake Brooker (Durham University). “This is why we estimated that it was important to share these new observations.”

By the way, Van Leeuwen and his colleagues are not quite sure if the trend of the grass is really useless.

Van Leeuwen notes: “This could also serve a social objective. In copying someone else’s behavior, you show that you notice and perhaps even as this individual. He could therefore help strengthen social ties and create a feeling of belonging within the group, just like in humans.”