Great Apes Know Just How Much to Annoy One Another

In the late aughts, while working on the island of Jersey, in the United Kingdom, Erica Cartmill found herself staring at a daughter giving her mother some grief.

The little one was waving a stick in her mother’s face and then yanking it back when her mother reached to snatch the object away—a performance so persistent, so targeted, Cartmill told me, that it was almost impossible for the grown-up to ignore. Cartmill was immediately reminded of kids threatening to poke each other in the back seat of a car. Only, the pair she was watching weren’t human: They were an orangutan and her two-year-old, lazing about in the straw at the island’s local zoo.

At the time, Cartmill didn’t know how to parse what she’d observed. She was wrapping up her Ph.D. on gestural communication in great apes, but this “didn’t really fit into any of the categories that I was looking at,” she told me. Years later, Cartmill, now an anthropologist at UCLA, recognizes the young orangutan’s capers as a form of teasing: one individual provoking another over and over, in a bid for their attention. “It was something they both were clearly enjoying,” she said, even if it was also “a little bit annoying.” The little orangutan wasn’t transfering the stick to her mother or necessarily inviting her to play. Rather, she seemed to be experimenting with her mother’s expectations by attempting to violate them—perhaps even approximating “the format that you get in something like a joke,” Cartmill told me. In the proffered object was the setup; in the surprise retraction, an amusing punch line.

In the years since that encounter, Cartmill and her colleagues have analyzed 75 hours of footage from two zoos of chimpanzees, bonobos, orangutans, and gorillas exhibiting similarly impish behavior. As they argue in a new paper, the great apes’ impulse to playfully prod, tickle, and steal from one another are the building blocks of humor—findings that suggest that “the precursors for joking were there in the last common ancestor” we share with other great-ape species, says Laura Lewis, a primatologist at UC Berkeley, who wasn’t involved in Cartmill’s work. Animals may have been poking at one another in fun for 13 million years or more; today, these goofy behaviors could help us understand how well apes know one another’s minds.

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Teasing can look like a silly game, but playfully pestering others may carry evolutionary perks too. It can strengthen social bonds and provide animals with intel on how tolerant their friends and family are, Marina Davila Ross, a comparative psychologist at the University of Portsmouth, told me. Teasing is also impressive, demanding social savvy and foresight: To push past others’ psychological limits, successful provocateurs must be intimately familiar with them.

Over many decades, researchers have documented examples of great apes seeming to appreciate a kind of physical comedy: a chimp coyly offering a ball and whipping it back when another tries to accept it; an orangutan magnanimously extending an arm to another and then quickly retracting it, almost like a high-five fake-out. But Cartmill’s study is the first to systematically document the behavior across four species—and to routinely check the responses of the ape being teased.

The videos the team analyzed would look familiar to anyone who’s spent time in a nursery, in part because they so often capture young apes bugging their parents. In one, a young chimp lightly smacks her mother’s back, then sprints a short distance to cautiously gauge her response; in another, a male gorilla ambushes his mom from behind with a galloping jump attack. Another shows a tiny orangutan incessantly batting her father’s head with a rope swing. A few apes even seemed to get a kick out of invading one another’s personal space, leaning quite uncomfortably close, until their faces almost touched. Each interaction was just vexing enough to prompt a response—but seemed to stop short of being aggressive or mean-spirited. Many of the adults ignored the badgering, especially at first; a few swatted at their tormentors. Largely, though, they seemed content to indulge, or even teased right back—though when they did, it tended to involve less hitting and body slamming, and more tickling or stealing.

Across ages, the apes’ behaviors are “very much comparable to what preverbal infants show,” Isabelle Laumer, an anthropologist at UCLA and one of the study’s authors, told me. Infants as young as eight months old offer objects to their parents, only to pull them away; they’ll interfere with others’ activities, then scour their friends’ faces to confirm that they’re still game. In watching her great-ape study subjects, Laumer told me, she’s often reminded of her own young niece and nephew, who are constantly delighting themselves by pranking their parents.

Great apes, of course, aren’t exactly like human kids—and the motivations of other animals are tricky to parse. Marcela Benítez, an anthropologist at Emory University who wasn’t involved in the study, told me she wasn’t completely convinced that the great apes had set out to provoke; some of the juveniles, for instance, might have stumbled onto what looked like teasing after their behaviors earned them a response they liked. Other experts, though, told me they saw some hallmarks of intent. The animals were checking the facial expressions of the targets of their teasing, Lewis told me. And when they were ignored, they persisted in their antics, often escalating their intensity, Vasudevi Reddy, a psychologist at the University of Portsmouth, told me.

Teasing, which shares some of the behavioral features of aggression, isn’t always good-natured. And when smacking, snatching, or breaching another’s space goes too far, it can easily warp an interaction into torment or bullying, Reddy pointed out. Great apes are not immune to ill intent: They routinely gang up on members of their community that they see as weak, by stealing food, ostracizing them, or even resorting to serious violence.

But when truly meant to be playful, Cartmill told me, teasing can be delightful—the basis of flirting, the start of a friendship, the fodder for the secretive camaraderie of a clever inside joke. Public teasing among friends or family can show the strength of a bond to the rest of the world, by demonstrating that they have enough mutual understanding that provocations that might seem mean are all in good fun.

Successful teasing, after all, does rely on the teaser and teasee being in cahoots, to some degree. The instigator has to catch a recipient in a good-enough mood, and then torment them just lightheartedly enough that their actions won’t be misinterpreted. The notion that nonhuman animals are clued in to what’s happening in one another’s minds has been controversial among animal-cognition researchers. But Reddy told me that teasing could be an additional clue that nonhuman primates routinely guess at what other individuals are thinking, and use that intel to guide their own actions and further refine their social instincts.

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Cartmill told me she’s stopping short of attributing humor or joking to these animals—qualities that tend to be linked to play with language and culture-specific norms. But great apes (who, by the way, can laugh) could yet display those traits. Taught to use sign language, Koko the gorilla was known to sometimes lob what could be seen as wisecracks: When her keeper Penny would ask the gorilla how to brush her teeth, Koko, who knew the sign for toothbrush, would occasionally answer “Foot,” and give a goofy smirk.

Several experts told me they suspect that these kinds of teasing behaviors, the precursors of joking, could be present in other animals too—especially in highly social, intelligent mammals such as elephants, or in other non-great-ape primates. Teasing may even cross species: Researchers have seen chimpanzees doing a playful bait and switch with bread that they offer to hens; dogs might do something similar when they play keep-away during fetch. Michelle Rodrigues, a biological anthropologist at Marquette University who wasn’t involved in the study, told me that the team’s work has prompted her to rethink her own interactions with her spider-monkey study subjects, who would sometimes sneak over to playfully tug on her hair. Rodrigues doesn’t know if those primates have a true sense of humor about the situation. But she herself does. “Maybe,” she told me, laughing, “that was the beginning of us building a social relationship.”