Great apes have a penchant for joking and clowning around, according to a new study — a finding that sheds new light on the origins of human humor.
All species of great apes tease, tweak and occasionally torment their peers and older relatives — then stand back to watch the results, according to findings published on Tuesday in Royal Society B.
The paper suggests that humor is a widely shared characteristic of the ape family tree, pushing back the origins of “playful teasing” in humans to at least 13 million years ago, when great ape species began to split.
It also offers a foray into a tantalizing new line of inquiry that has emerged over the 21st century: the idea that play and not-immediately-practical behaviors may have a bigger role in animal life than was generally assumed in the 20th century.
“We’re pivoting to entertain the possibility that animal minds are not always serious — not always about the next action needed for survival,” said co-author Erica Cartmill of the University of California, Los Angeles (UCLA).
“It’s a serious study of a non-serious topic,” she added.
In the footage gathered by researchers, members of all four groups of great apes — gorillas, chimpanzees, bonobos and orangutans — display the kinds of needling, provocative and playfully obnoxious behavior familiar to anyone who has spent time around young children.
The behavior, somewhere between play and aggression, followed a consistent trajectory. When apes were sitting around and relaxed, one ape — generally though not always a youth — would size up a target, generally an adult.
Then, the teaser would deliberately provoke the target, usually by poking, hitting, pulling on them or leaping on top of them — then stand back and wait for a reaction.
This step at the end — which primatologists call “response looking” — was “especially interesting,” said lead author Isabelle Laumer, a primatologist at the Max Planck Institute.
“They actually look towards the target, probably because they want to see their reaction,” Laumer said. If they didn’t get a reaction, the teaser would generally try again — only now at a higher intensity.
A few other patterns stood out. First, adults and juveniles joked around with each other in different ways: A youth might hit an adult, while an adult would only poke or tickle a youth.
And while young primates’ closest companions are often their mothers, moms generally weren’t the targets of teasing — though older sisters disproportionately were.
Adults usually greeted this teasing with halfhearted rebukes or retreats — pushing the teaser away, getting up and moving somewhere else — although in about a third of cases they reacted indulgently or playfully.
And while patterns of teasing were very consistent across the different species of great apes, among orangutans — a species known for their flowing orange locks — hair-pulling was far more popular as a means of getting attention than it was among their comparatively short-haired cousins like chimpanzees and bonobos.
These findings — like many from the emerging research into animal cognition and sociality — straddle the obvious and the revelatory.
On one hand, the findings represent a corroboration by science of something that anyone who has visited a primate enclosure at a zoo has had a good chance of seeing.
In her previous work with great apes, Laumer said, “I observed in the zoo — they sneak up and pull on [each other’s] hair from behind.”
This sort of behavior is well-represented in scientific literature, noted by such luminaries as Jane Goodall or Frans de Waal.
“Youngsters in the Arnhem Zoo chimpanzee colony frequently ‘bother’ adult group-members,” wrote primatologist Otto M.J. Adang in a classic 1986 paper.
Time and again, Adang wrote, younger chimpanzees would size up adults and “throw sticks and sand at them, hit them from behind, etc., and dash away immediately. This occurs without apparent instigation and in spite of the fact that they may be punished.”
For decades, however, scientists tended to categorize this behavior as belonging to either low-level, overt aggression — described by words like “annoying,” “pestering” or “harassment” — or as play.
In Adang’s studies, for example, he specifically excludes such provocations from consideration as “teasing” if they’re carried out with a characteristic primate expression known as a “play face.”
And one 2017 paper refers to a similar cluster of behaviors among bonobos as the “harassment of adults by immatures.”
But this misses the way in which teasing, joking and clowning around exist somewhere between the two categories, UCLA’s Cartmill said.
“There is a type of teasing that’s in the middle,” she said. “It has some characteristics of aggression — you’re doing it to provoke a reaction — but within close relationships that are playful.”
One key element of these interactions, she noted, is that “they happen when animals are in a relaxed state — sitting around like two kids in the back of a car seat on a road trip, poking each other. Or offering something and pulling it back, or leaning really close to put my face by yours — ah, now you’re annoyed.”
These behaviors may be playful, she said — but they’re something distinct from play, too. “The non-scientific term is: They are their own deal.”
Cartmill acknowledged that this comparison of human kids in a backseat to a lounging troop of chimpanzees may sound a lot like an old bogeyman of animal behavioral science: anthropomorphism, or the idea (ubiquitous in, say, children’s cartoons) that animal behaviors are analogous to human ones.
“Apes aren’t telling sophisticated jokes,” she said — noting that even the simplest and most groan-inducing “dad joke” is often at a level of complexity that requires not just the ability to speak but deep fluency in a culture.
To launch an annual lecture on this point, Cartmill shows undergraduates a list of “horrible eye-rolling jokes,” like a cartoon that shows a pickle in a top hat and cane with the caption “I’m kind of a big dill.”
“To get that joke — and even to understand why it’s a horrible joke — is something no other species can do,” she said.
But in a discipline that has often seen animals as akin to complex machines running unconsciously on program-like inputs of stimulus and response, she said, obvious-seeming comparisons between humans and animals can offer a “reality check” to help scientists ask better questions.
And many of the comparisons are tantalizing. Laumer, the Max Planck primatologist, pointed to a 2021 study by the paper’s UCLA co-author Sasha Winkler, which found a strong overlap between human laughter and “play vocalizations” in primates.
(That study conjectured that the characteristic “ha ha” of human laughter had “evolved from an auditory cue of laboured breathing during play.”)
Other studies have shown that one of the foundations of the idea that humor is human-specific — that it requires at least enough language to understand why that pickle is a big dill — turns out not to be true.
Human infants as young as eight months, for example, are already beginning to play with others’ expectations, as a 2015 paper on the subject found. “Before they speak or walk or crawl, infants joke,” wrote the scientists Vasudevi Reddy and Gina Mireault.
“Even in the first year of life, infants create and maintain novel humorous initiatives,” they found, which included “actively looking for opportunities to elicit others’ laughter by playing the ‘clown’ and playfully provoking others by teasing them.”
Like those practiced by young great apes, these toddler jokes are not particularly complicated: They may involve, for example, broad comedy gestures like wearing a shoe on one’s head, or offering a parent a toy and then pulling it back.
This kind of early playful teasing — which Tuesday’s study suggests is common among great apes — may form the building blocks of what in our species ultimately presents as, say, political cartoons and stand-up comedy, Cartmill said.
But for both young apes and young humans, she said, it also may teach valuable lessons about social norms and about the specific character of individual relatives — how much you can poke your brother before he gets legitimately mad — as well as reaffirming and strengthening those relationships. (As Laumer said, quoting a German proverb, ”They who love each other, tease each other.”)
One core element of humor, after all, is that it’s social: Both young apes and human children seem to draw their understanding of what is funny — and what is scary or alarming — from how adults and older juveniles react.
For toddlers, Mireault and Reddy write, “It is the emotional reactions of other people — their laughter, amusement, indignation, surprise, annoyance and puzzlement — which are the key to their funniness, which ‘opens the doors’ of humor.”
This social context now represents the source of some of the biggest unanswered questions about the building blocks of humor in animals. Because the scientists looked at small groups of captive apes, they weren’t able to investigate how joking functions in more numerous or complicated social groups.
For example, is teasing more common in front of others than it is when both parties are alone — and does it matter if those others are socially popular? And how do these behaviors change in chimpanzees in the wild?
“I’m not saying apes have in-jokes,” Cartmill said, “but they might have cultures of teasing that differ group to group.”
Seeing those differences — or noticing them in species that are further from us than apes — will require moving past old assumptions of what animals are capable of, she argued.