Baby Chicks Know That “Bouba” Is Round and “Kiki” Is Spiky

A newly hatched chick stands in a small arena, barely hours old, still wobbly on its feet. On a screen before it, two shapes glow side by side — one with soft, pillowy curves, the other a jagged starburst. A hidden speaker begins repeating a single nonsense word: bouba, bouba, bouba. The chick toddles towards the round shape and stays there, exploring it for more than three minutes. When the experiment is run again with kiki playing instead, different chicks make a beeline for the spiky one.

This is the bouba-kiki effect, and until now we thought it was ours. Humans across virtually every culture tested — from Tamil speakers to Mandarin speakers, from preliterate toddlers to university students — reliably match the made-up word bouba to blobby, rounded forms and kiki to angular, pointy ones. The intuition is so consistent that linguists have long suspected it might be a clue to how our ancestors first tied meaning to sound, perhaps one of the building blocks of language itself.

But chickens don’t have language. They can’t shape their beaks to say bouba, and they have roughly zero interest in linguistics. Yet in a study published this week in Science, Maria Loconsole, a comparative psychologist at the University of Padova in Italy, and her colleagues show that domestic chicks make exactly the same sound-shape connections we do — and they do it within their first day of life, before any learning could plausibly account for it.

The results land rather awkwardly for one popular theory. If the bouba-kiki effect were a stepping stone towards human language, you’d expect it to be, well, human. Finding it in a bird whose lineage split from ours somewhere around 300 million years ago suggests the phenomenon is far older and more fundamental than a precursor to speech.

Loconsole’s team ran two experiments. In the first, 42 three-day-old chicks were trained to navigate around a panel showing an ambiguous shape — one with both rounded and spiky edges — to reach food. Then, during testing, the birds faced two panels simultaneously, one round and one jagged, while either bouba or kiki played from a speaker. Across 24 trials, the chicks consistently chose the round panel when they heard bouba and the spiky one when they heard kiki. A control group hearing silence or classical music just showed a mild baseline preference for the round shape, nothing like the targeted matching seen in the experimental birds.

The second experiment tightened things considerably. Forty chicks were tested within 24 hours of hatching — no training, no social housing, no reward. Each bird simply heard one word while both shapes appeared on screen. Eighty per cent of chicks hearing bouba approached the round shape first, spending on average roughly 200 seconds exploring it versus about 58 seconds on the spiky alternative. The pattern flipped for kiki.

Because these were animals tested at the very start of life, with their experience carefully controlled from the moment they broke through the eggshell, this isn’t something they could have picked up from the environment. It points instead to an innate perceptual bias — a brain already wired, before any experience, to link certain kinds of sounds with certain kinds of shapes.

Aleksandra Ćwiek, a linguist at Nicolaus Copernicus University in Toruń, Poland, who was not involved in the study, told Scientific American that the finding was mind-blowing given that birds and mammals parted ways on the evolutionary tree some 300 million years ago. She and her colleagues demonstrated in 2022 that the bouba-kiki effect holds across diverse cultures and writing systems worldwide. But the chick data, she suggested, actually makes the link to language evolution less interesting — because whatever this is, it clearly predates language altogether. What it reveals instead, she said, is something deeper about cognition itself: the capacity brains have for connecting information across the senses.

There is, of course, the question of the apes. Previous studies tested chimpanzees, gorillas and the bonobo Kanzi on bouba-kiki tasks — and they all failed, which at the time seemed to reinforce the idea that this was a uniquely human trick. But Loconsole and others have argued those results may have been muddied by the animals’ extensive prior training. Kanzi, who recently passed away, had learned to match some 500 visual-auditory pairs over years of language research; it’s possible that when he encountered these new nonsense words, he tried to work out their meaning rather than following a gut-level association. One long-standing explanation for the effect — that it comes from the shape your mouth makes when pronouncing each word, lips rounding for bouba, tongue tapping sharply for kiki — can probably be ruled out too, given that chickens obviously can’t produce either sound.

So what is going on? The answer might lie in the physics of the everyday world. Round objects, when they hit a surface or roll, tend to produce lower-frequency, more continuous sounds than angular ones of the same size. A built-in ability to match what you see with what you hear — to expect that smooth-sounding things look smooth and sharp-sounding things look sharp — could help a newborn animal make sense of its surroundings fast, perhaps to locate food or dodge a predator.

The bouba-kiki effect, in other words, may not be about language at all. It may be about survival. As Loconsole told Scientific American, even if language is unique to humans, that doesn’t necessarily mean it springs from an ability that is.

Study link: https://www.science.org/doi/10.1126/science.adq7188