Great apes tease, play with each other in ways similar to humans, new study reveals

Great apes aren't so different from humans when it comes to certain social interactions, they too enjoy making funny faces, poking one another, randomly pulling hair and other forms of teasing, according to a recently published study.

The study done by cognitive biologists and primatologists from the Max Planck Institute of Animal Behavior in Germany and three U.S. colleges reported evidence of "playful teasing" in four great ape species — orangutans, chimpanzees, bonobos and gorillas.

Erica Cartmill, a professor at the University of California Los Angeles, told USA TODAY that she and her three colleagues started the study in 2020. It involved observing videos of great apes interacting with each other at the San Diego Zoo and the Leipzig Zoo in Germany.

How did researchers conduct the study?

Cartmill said that the idea behind the study originated after the team received a grant in 2019 from the Templeton World Charity Foundation to do work on playful teasing. The team had various interactive studies planned but the COVID-19 pandemic halted their plans, so that's when Federico Rossano, a professor at the University of California, San Diego, provided 75 hours of archived video he collected for a different study, she said.

"We were actually able to use the video he had, and look through the video, to find places where apes were interacting with one another in a way that wasn't fully play and wasn't fully aggression," Cartmill said. "It was sort of somewhere in the middle."

Great apes exhibited playful, mildly harassing and provocative voluntary interactions during the study. The teasing ape's actions, bodily movements and facial expressions were studied, in addition to how the targets of the joking responded, according to the study published Wednesday by the Proceedings of the Royal Society B: Biological Sciences.

The teasing primate's intentions were also studied by further observing if the behavior was directed at a specific target, if the joking persisted or intensified and how long it took for the teasing ape to respond to the target, according to the study.

Challenges surrounding the study

Rossano told USA TODAY the team focused on one group per primate species, so the species differences should be taken with a grain of salt. The orangutan group and the gorilla group had four members while the chimpanzee group had 17 members, he said.

"One would need to compare different groups from each species and ideally groups of different sizes to make sure the effects are not simply reflective of the number of individuals in the group or idiosyncratic temperaments of the individuals observed," Rossano said.

A limitation of the study was that the videos observed primarily focused on juvenile apes, not adults, Cartmill said.

"I definitely think that young apes do this (playful teasing) behavior more," she said. "... But statistically we can't really prove that because we didn't collect the same number of hours of video from adults and juveniles."

What 'teasing behaviors' did the apes exhibit?

The study showed that the apes engaged in 18 "distinct teasing behaviors" that were primarily used to elicit a response. Repeatedly waving or swinging a body part or object in another ape's face, hitting or poking another ape, staring closely into other apes' faces, disrupting targets' movements and pulling on their hair were all frequently seen as teasing behaviors, Cartmill said.

"These aren't actions that we saw for the first time," she said. "These are things that if you go to the zoo and you look at apes you will recognize."

Cartmill said the point of the study isn't to show that this is the first time anyone has seen these behaviors, but it's to make people look at them differently as "distinct kinds of behavior."

"It's very similar to the kind of joking you see in human infants right around their first birthday," she said. "Children start doing playful things that push boundaries in different ways. They'll take a shoe, put it on their head as a hat and find it hilarious."

Not to be confused with regular play, playful teasing in great apes is "one-sided," only initiated and continued by the teaser and is rarely reciprocated, Cartmill said. The teased apes also don't often smile, or what Cartmill calls primate "playface," and they don't exhibit "hold" gestures that indicate their intent to play.

What does the study say about human evolution?

Isabelle Laumer, a post-doctoral researcher at MPI-AB and the first author of the study, said in a news release that playful teasing primarily happened when target apes were relaxed.

“Similar to teasing in children, ape playful teasing involves one-sided provocation, response waiting in which the teaser looks towards the target’s face directly after a teasing action, repetition, and elements of surprise,” she said.

The "idea of the unexpected" is also shared between great apes and human children, according to Cartmill.

"Where human children will sort of offer an object and then pull it back at the last second and laugh, you see a very similar behavior in apes," she said. "... I think this is something that's really at the heart of these simple forms of joking and ultimately forms the foundation for more complicated forms of humor."

Rossano said while teasing in humans is often negatively associated with bullying, playful teasing is a "signal of the strength of our bonds with others."

"We playfully tease people we care about and people we trust will see the playfulness in our behavior," he said. "If great apes engage in playful teasing, it also reminds us that teasing is independent of language and not human unique."

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Looking at the study from an evolutionary lense, Laumer said the playful teasing exhibited by the four great apes and teasing and joking in human infants suggests that "playful teasing and its cognitive prerequisites may have been present in our last common ancestor, at least 13 million years ago."

"We hope that our study will inspire other researchers to study playful teasing in more species in order to better understand the evolution of this multi-faceted behavior," Laumer said in the release. "We also hope that this study raises awareness of the similarities we share with our closest relatives and the importance of protecting these endangered animals.”

The team is in the process of creating a website (playfulteasing.org) to allow people to submit stories involving social interactions they have seen between animals, Cartmill said.

Sasha Winkler, a graduate scholar at UCLA, also helped in the study.

This article originally appeared on USA TODAY: Great apes tease each other just like humans do, new study reveals