The evolutionary case for a little roughhousing
A variety of studies are showing that rough-and-tumble play is important for animals and kids alike.
Gordon Burghardt kept a lion cub named Meg in his home at the behest of the Knoxville Zoo. To help Meg get out some energy, Burghardt and his wife would often play with Meg in their wooded, unfenced backyard. One day, a neighbor’s dog appeared, tail wagging. As an ethologist—a scientist who studies animal behavior— Burghardt could see that the dog was giving clear signals that he wanted to play, not fight, but would the lion cub be able to read them? After all, these are two creatures separated by around 45 million years of evolution.
The cub gently placed her paw on the dog’s back, and the dog lowered his head and stretched out his legs—a gesture that animal behaviorists call the “play bow.” Then, he raced away and the cub chased after him. As Burghardt watched the two animals negotiate a rollicking game of “tag,” he was astonished.
“They immediately understood the signals—that it wasn’t adversarial,” said Burghardt, a professor at the University of Tennessee, and author of The Genesis of Animal Play: Testing the Limits. “It’s remarkable that two animals so different can communicate their intentions at all.”
The encounter took place roughly 50 years ago, when animal play was not seen as a topic worthy of scientific investigation. “People thought it was too anthropomorphic,” Burghardt says. But now, what once looked like frivolity is proving fundamental. Driven by ancient circuits deep in the brainstem, rough-and-tumble play takes remarkably similar forms across many species, and it’s turning out to be far more essential than we’ve assumed. When animals are deprived of it, studies show, they don’t just miss out on fun — they grow up socially impaired, particularly when it comes to interacting with the opposite sex.
“It's absolutely essential for social mammals to engage in a wide variety of play, both for brain development and for them socially — and that includes humans, too,” says psychiatrist and play researcher Stuart Brown.
(Scientists put sharks in a tank full of toys. What they saw surprised them.)
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The shape of fun
As two young rats tussle, they compete to nuzzle and nip the napes of one another’s necks. The rat who has the advantage often cedes it by rolling onto its back, or by only partially executing defensive maneuvers. Bites are gentle, dominance is fleeting, and a single squeak is enough to end the bout.
Magpies also follow these basic rules. As two birds compete to peck one another’s heads, they never use full force, take turns winning, and stop when either player has had enough. If you’ve ever watched kids wrestle, you’ve probably seen the same guidelines in effect, says Sergio Pellis, a neuroscientist at the University of Lethbridge and co-author of The Playful Brain: Venturing to the Limits of Neuroscience. Indeed, roughhousing sometimes brings out our inner monkey.
“You will find examples, particularly in those first two or three years of life, where kids engaging in rough-and-tumble play are trying to bite one another,” Pellis says. “My guess is that humans still have some of the residual biting that is typical of apes and Old World monkeys.”
The signals animals use to keep things friendly can also be surprisingly similar across species, notes Burghardt’s former student, Heather Brooks. Brooks, now a postdoctoral researcher at the University of Colorado, Boulder, recently examined more than 200 bouts of interspecies play, most of which she found online. In many videos featuring primates, you can spot the loose, open-mouthed “play face,” which may be the foundation for human laughter. As for the play bow made famous by dogs, it’s also used by lions, magpies, and a thrush-like bird called the Arabian babbler. Bowing may communicate “this is play, not a real fight” because briefly breaking eye contact makes the player slightly vulnerable, Brooks says.
“Maybe it's part of the self-handicapping that the animals do, to indicate like they're not going to be super aggressive,” she says.
The drive to play and many of the basic rules are deeply ingrained. Rats whose cerebral cortex has been removed still engage their littermates in wrestling matches, initiate play just as often, and even switch roles. Without a cerebral cortex, however, the rats stop making “context-dependent adjustments,” Pellis adds, such as not playing too rough with a more dominant male.
If play is governed by the brainstem, that means it’s as primal as hunger, fear, and other ancient motivational systems.
While most mammals probably have the play drive, not all of them can express it, Pellis adds. Species with short, precarious lives have little room for exuberant, energy-expensive play. Mice, for instance, are born with most of the skills they need to survive. They don’t have to exercise fine-grained judgement and navigate social hierarchies— two abilities that play seems to build.
“The kinds of refinements that play can provide will only be of use to animals that have a kind of social life and a degree of longevity that they can utilize those skills,” Pellis says.
Play’s paradox
For a behavior to count as play, it can’t have any apparent or immediate function—but few wild animals have the extra calories to burn doing pointless things. In addition to requiring a lot of energy, wrestling with your littermates is noisy and conspicuous. Two play-fighting rats, for instance, could easily attract the attention of a hungry hawk. And yet, many young mammals spend up to 20% of their day tussling with their peers, according to The Playful Brain.
So, what’s the hidden purpose of play-fighting? Most nature documentaries assert that rough-and-tumble play gives young animals a way to practice behaviors they will need as adults. That’s a reasonable assumption, but if you look closely, animals don’t actually employ difficult or typical moves in their play fighting, says Gisela Kaplan, an ethology professor, emeritus, at the University of New England, Australia and author of Bird Bonds. For instance, young elk often play by locking horns, but never by butting heads -- a more aggressive move that’s reserved for serious fights.
“Play offers no obvious advantage in skill acquisition,” Kaplan says. “But it does help you learn to manage fear.”
Researchers have put that idea to the test by depriving young rats of the opportunity to play. The results? They grow up to be anxious wrecks. Encounters with other rats rattle them easily, and they tend to overreact, responding to ambiguous cues with aggression or defensive withdrawal. Later, these social miscalibrations show up as sexual incompetence. In addition to misreading others’ amorous overtures, play-deprived male rats have been observed trying to mount female rats from the wrong end.
Pellis and other researchers have peered into play-deprived rats’ brains and found some neural underpinnings for these social and emotional misfires. In the brain’s orbitofrontal cortex, a region that helps animals interpret social signals, neurons’ dendrites sprawled every which-way—suggesting that they never got the pruning they needed to develop efficient, streamlined connections. Meanwhile, the neurons in the rats’ medial prefrontal cortex, which downregulates emotional responses, don’t have enough branches. Taken together, this suggests a system out of balance, one that can’t take context into consideration when assessing threats.
These findings point toward a purpose for play that’s less obvious than the practice hypothesis. Play-fighting links ancient, brainstem-driven emotional and motivational systems with the higher cortical circuits that can judge when to apply the brakes, Pellis says.
“Play fighting is actually not practicing your fighting skills, but it is helping train your prefrontal cortex to figure out, ‘How should I modify my behavior relative to the situation?’” he says.
Play-deprived kids
It would be unethical to deprive children of opportunities for roughhousing just to see what happens, but there’s an unintentional experiment in progress on that very question. Over the last few decades, unstructured playtime has been replaced with scheduled activities and nonstop supervision, with one 2018 survey finding that American children have 35% less outdoor free-play time than their parents did. Another study, in 2024, found that many parents say they support risky play, but only 78% actually allow their kids to engage in roughhousing. Moreover, parents taking risk-tolerance surveys regularly rank roughhousing as one of the most anxiety-triggering activities kids can do, alongside climbing to the tops of trees or roaming unsupervised.
Given this reality, perhaps it’s unsurprising that children today are showing many of the same effects of play deprivation that scientists have observed in the lab. Anxiety, for instance, is on the rise -- and part of the problem might be that children aren’t learning to modulate their automatic fear responses by tussling with other kids.
“Rough-and-tumble play is scary,” says Kaplan. “Sometimes you get pinned, sometimes you feel out of control, but then everything is fine and your stress levels go down very quickly.”
Play-fighting also trains animals to assess another creature’s motives and physically adapt to their movements—two key abilities for mating, Pellis says. In rats, depriving young animals of rough-and-tumble play leaves them strikingly inept at courtship later in life. That research offers a provocative lens on recent human trends. According to the Survey Center on American Life, just 56 percent of Gen Z had a romantic relationship as a teenager, compared with 78 percent of Baby Boomers and 76 percent of Gen Xers. And between 2000 and 2018, the percent of young adults who haven’t had sex in the last year tripled among men, and doubled among women.
Overall, humans seem to be depriving themselves of play while binging footage of animals playing online. Videos of unlikely playmates are particularly popular, says Brooks, who identified more than 200 such videos in a recent analysis, including a crocodile wrestling gently with an otter, and a dog playing tag with a tortoise. As with the lion cub and neighbor’s dog that first astonished Burghardt decades ago, the appeal may lay in watching successful cross-species communication, and to the vicarious pleasure of witnessing unbridled joy.
“We should probably get offline and follow their lead,” she says.
