Chimps and tools: The boys play, while the girls learn

Researchers find that chimpanzees and bonobos, humans' closest cousins, interact with objects in distinct ways depending on their gender.

Courtesy of Kathelijne Koops
An adult male chimpanzee uses stones to crack nuts.

When children play with toys, they learn useful skills for adulthood. Young chimpanzees are no different, say scientists. 

According to a paper published Wednesday in the journal PLOS ONE, immature chimpanzees interact with objects differently depending on their gender

The young males engaged in object manipulation more frequently, and they used objects for play more often than the females did. The females used objects to achieve goals, explore their surroundings, or for other useful tasks, the researchers reported. 

A team of researchers led by University of Zurich anthropologist Kathelijne Koops, observed young wild chimpanzees in Uganda. Initially they were perplexed by what they saw. 

Adult female chimpanzees have been observed using tools more frequently than males, which led researchers to suppose that young female chimps would manipulate objects more too. But that was not the case. 

“It became clear that in the male chimpanzees’ object manipulation was mainly play. A lot of it was running around with a twig or chasing each other with a branch, with leaves or something like that,” Dr. Koops says in an interview with The Christian Science Monitor. “In the females it was much less play dominated and more goal directed, more diverse.”

“That does suggest that they are in a sense practicing or ‘preparing’ for tool use in adulthood,” she says. “Whereas in the males it looks like this object manipulation in play might be more linked to practicing motor skills and potentially male-specific behavior such as dominance displays.”

Humans, it turns out, aren't much different.

“When I started digging into the human literature, I found that often they actually report a male bias in object manipulation as well,” says Dr. Koops. But that behavior, too, was more about play than tool development. “We do see a similar pattern in humans and chimpanzees which might suggest that our common ancestor had a similar behavior.”

Scientists long held that what sets humans set apart from other animals is our use of tools. But humans’ hairy cousins have been spotted using tools for foraging, cracking open nuts, and other uses. 

Jane Goodall was the first to spot a chimpanzee using tools, when in 1960 she spotted a male using a piece of grass to pull termites out of their mound. 

When a chimp "fishes" for termites, as it's called, he or she pushes a stick or piece of grass into the termite mound. The termites latch onto the object, and the chimpanzee pulls the stick back out and swipes the crunchy meal off the tool and into his or her mouth. This method has also been observed with ants and other bugs. 

Improved tool use

The chimpanzees also chose different tools as they matured. 

“The youngsters below three years old manipulated much more leaves. As they got older, they started focusing more on sticks, which is the tool type that they use in this community,” says Koops. 

“It looks like as they get older, the chimps are starting to focus more on what is actually a relevant tool material.”

Courtesy of Kathelijne Koops
A young chimp male plays with a leaf.

Bonobos

Chimps are not the only close human cousin that researchers observed. In the Democratic Republic of Congo, they also watched the chimpanzees closest relative, the bonobo.

“The bonobos—they’re as closely related to us as chimpanzees—use very few tools and no tools in foraging,” says Koops. 

So the researchers weren’t surprised to see the young bonobos play with objects socially, which “fits their character as the playful apes,” Koops says. 

There was no sex difference among young bonobos, they all ran around playing with each other.

“We knew that chimpanzees use more tools than bonobos, but we didn’t know so much as where this difference comes from,” says Koops. “It seems to be something that’s intrinsic.” Chimpanzees intrinsically seem to be more object-oriented than bonobos, she says. 

Courtesy of Kathelijne Koops
Bonobo youngsters engage in social play.

The researchers become the tools

“Even after studying chimpanzees for 12 or 13 years, they still surprise you very often,” says Koops. 

While Koops was observing the chimpanzees one day, she witnessed a special case of social tool use.

“We had one adult male who was fighting for the top rank in his group. He was very comfortable with people,” having grown up with researchers around, she says. “He wasn’t afraid of us.”

“The two other males were much less comfortable with us because they were older, so they weren’t as used to us,” she explains.

“One day when the other two males were forming a coalition against him, he just came to sit behind us, basically using us as a tool against the males,” Koops says. 

Courtesy of Kathelijne Koops
A chimp engages in object play.

Despite being covered in hair, chimpanzees and bonobos are remarkably close relatives to humans. We share about 99 percent of our DNA with these apes. 

Being such close cousins, we could learn a lot about ourselves through studying these primates.

“We can learn so much about how we became the way we are and how we evolved to be who we are today from our closest living relatives, the chimpanzees and bonobos,” Koops says. 

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