In a beech forest at Arthur’s Pass, on New Zealand’s South Island, a researcher named Raoul Schwing set up a speaker and pressed play. What came out was not music, not an alarm call, not anything a human would recognize as meaningful. It was the warbling play call of a kea, the world’s only alpine parrot, a bird known for stealing windshield wipers and dismantling tents out of what can only be described as curiosity.
The wild keas nearby did not gather around the speaker. They did not investigate the sound. They simply started playing. Tumbling through the air, wrestling each other, tossing sticks back and forth, some of them alone, with no obvious trigger except a sound they had heard a moment before.
What Schwing had captured was not a call to action. It was something closer to contagion. The kea’s play call did to other keas roughly what your laughter does to the people sitting near you: it didn’t ask them to join in, it simply made them feel like joining in. Schwing called it positive emotional contagion. Most people would call it something simpler: the sound was, by every functional measure available to science, a laugh.
This single experiment, published in 2017, became one entry point into a body of research that has only deepened in the years since. The question it forces is not whether animals laugh in some loose, anthropomorphic sense. The question is why laughter, in one form or another, keeps showing up in species that share almost nothing else: parrots, rats, dolphins, dogs, chimpanzees, humans. Species separated by tens of millions of years of evolution, none of them copying the others, all arriving at the same solution.
What Laughter Actually Is
Strip away the social theater and laughter is, first, a biological event. A real laugh triggers a measurable cascade: cortisol drops, endorphins and dopamine rise, heart rate spikes briefly before settling lower than baseline. A genuine laugh can burn close to 75 percent more energy than sitting still, which is why some researchers half-jokingly call it inner jogging. None of this requires a sense of humor. It requires only the right kind of social, playful arousal, and a body built to release it through sound.
That distinction matters, because it’s the key to everything that follows. If laughter were really about jokes, it would make sense to find it only in species clever enough to construct one. Instead it shows up wherever play does, regardless of how sophisticated the species’ inner life appears to be from the outside. That tells you laughter isn’t a byproduct of intelligence or humor. It’s older and more basic than either.
Why This Should Matter to You, Specifically
Before going further into the animal kingdom, it’s worth being honest about what the biology means for the body you’re sitting in right now.
A 2024 meta-analysis pooling laughter intervention studies found an average 31.9 percent reduction in cortisol compared to control groups, with no evidence of publication bias propping up the result. UCLA Health has reported that a single laughter session can drop cortisol by as much as 37 percent, regardless of what triggered it or how long it lasted. This is not a placebo-shaped finding. It shows up reliably, across different populations, using different methods.
The downstream effects compound. Laughter measurably activates natural killer cells and T-cells, the immune system’s first responders. Newer clinical work from 2024 and 2025, much of it in vulnerable populations such as cancer patients and nursing students under acute stress, has found consistent reductions in anxiety and depression scores following laughter-based interventions. In older adults, sustained social laughter has been associated with lower dementia risk, likely through the same stress-and-inflammation pathway that links chronic cortisol exposure to cognitive decline.
None of this makes laughter a cure for anything. But it does make it something closer to a maintenance requirement than a luxury. The body treats laughter the way it treats sleep or movement: optional in the short term, costly to skip in the long term. Keep that in mind as the animal examples pile up. Every species below is, in its own way, running the same maintenance.
The Rat Nobody Suspected
In the late 1990s, neuroscientist Jaak Panksepp recorded something strange while studying play behavior in laboratory rats. During rough-and-tumble play, the animals produced a burst of vocalization at roughly 50 kilohertz, far above the range of human hearing. When Panksepp’s team tickled the rats by hand, mimicking the rough play of a littermate, the sound intensified.
Rats, it turns out, have ticklish patches of skin, just as humans do, and the rats that laughed most also played most, and preferentially sought out the company of other rats that laughed. None of this looks anything like a chuckle to a human observer. You would need ultrasonic recording equipment to know it was happening at all. But by every functional criterion researchers use to define laughter, social context, response to tickling, link to play rather than danger, it qualifies.
A Pattern Across Sixty-Five Species
In 2021, UCLA researchers Sasha Winkler and Greg Bryant set out to answer a simple question: how widespread is this, really? They combed the existing literature for any documented vocalization tied to play across the animal kingdom and found it in 65 mammal species and several bird species, from foxes and elk to killer whales and parrots.
The forms varied wildly. Dogs produce a breathy, forced pant, structurally distinct from ordinary panting, that researchers now formally call the dog laugh. Elk squeal. Elephants and sea lions, almost alone among the list, laugh loudly enough for a human to hear it from across a room. Most species, like the rat, laugh quietly, audible only to a play partner standing close.
What didn’t vary was the context. The vocalization always appeared during play, never during real aggression, never in response to pain or threat. Its function, across every one of these unrelated lineages, was the same: signal that what’s happening is not dangerous, that the rough-and-tumble of play fighting is exactly that and nothing more, and invite the recipient to keep going.
Why a Sound, and Why Now
Robin Dunbar’s work on primate social bonding offers a useful frame for why this signal might have evolved at all. Primates maintain social bonds through physical grooming, picking through each other’s fur, which releases endorphins in both the groomer and the groomed. The catch is that grooming is a one-to-one activity. It puts a hard ceiling on group size, since there are only so many hours in a day to groom your way through a social network. Chimpanzee troops, accordingly, max out around 50 individuals.
Human groups grew well past that ceiling, toward roughly 150, the figure now known as Dunbar’s number. Dunbar’s proposal is that laughter is what made the jump possible: a vocal signal that can trigger the same endorphin release as physical grooming, but in many listeners simultaneously rather than one. One person laughing in a group can lift the mood of everyone within earshot. It’s social bonding that scales.
The Strongest Evidence: Two Unrelated Brains, One Solution
If laughter were simply an inherited trait, passed down from some distant common ancestor to all the species that display it today, its presence in close relatives like chimpanzees would be unremarkable. What makes the case for laughter as a deep solution to a deep problem, rather than an evolutionary accident, is finding it in species that share almost no recent ancestry with us at all.
The kea is one example. Parrots and primates split from a common lineage so far back that the resemblance has to be convergent, not inherited. The bottlenose dolphin offers an even sharper case. Dolphins and primates diverged roughly 95 million years ago, and dolphins communicate underwater, acoustically, in an environment about as far from a primate social group as it’s possible to get.
And yet a study published in October 2024 found that bottlenose dolphins display an open-mouth facial expression, structurally similar to the relaxed play face documented in dogs, monkeys, and meerkats, used almost exclusively during social play and aimed deliberately at a visible playmate. More striking still: when one dolphin displayed the open mouth where a partner could see it, the partner mirrored the expression within a second, a rate of replication thirteen times higher than when the signal went undetected. This is rapid facial mimicry, the same mechanism behind a yawn spreading across a room of strangers, and it had never before been documented in a marine mammal.
A parrot, a rat, a dog, a dolphin, a chimpanzee. None of them copied the others’ homework. Each independently arrived at some version of the same answer: a signal, vocal or visual, that says this is play, not danger, and that spreads the good mood to whoever is close enough to catch it. It’s the same pattern I traced in What We Share With Elephants: when the underlying problem, in that case deep social bonding, in this case defusing tension and signaling safety, is shared across distantly related species, evolution tends to land on the same answer more than once.
What This Means, Coming Back Around
It’s tempting to treat the animal kingdom’s laughter as a curiosity, a fun fact about parrots and dolphins to mention at dinner. But the consistency of the pattern points somewhere more useful. When evolution solves the same problem the same way, independently, in species this distantly related, it’s usually because the problem is fundamental rather than incidental. Social animals need a way to defuse tension, to signal safety, to bond a group tighter than physical contact alone allows. Laughter is what keeps showing up as the answer.
Which brings it back to the cortisol numbers from earlier in this piece. Your body isn’t running some separate, modern, human-specific reward system every time you laugh. It’s running the same ancient machinery that calms a kea mid-tumble and synchronizes a dolphin’s open mouth with its playmate’s. The 31.9 percent drop in cortisol is not a side effect of human culture. It’s the maintenance cost of being a social animal, paid in full by every species smart enough, or simple enough, to have figured out how.