Chimpanzees catch yawns from robots - and lie down to rest

Chimpanzees have new companions in the world of yawning: androids. Researchers have discovered that chimpanzees not only yawn in response to a humanoid android’s yawn, but also exhibit restful behaviors like lying down.

The findings, published in the journal Scientific Reports, suggest a deeper behavioral and social link than mere imitation. This is the first real-time evidence of contagious yawning triggered by an inanimate humanoid model.

The study strengthens the idea that yawning can carry social meaning beyond automatic reflexes – even across species and material boundaries.

Chimps watched a robot with facial motions

Fourteen adult chimpanzees between 10 and 33 years old took part in the study. The chimps lived at the Fundació Mona Primate Sanctuary in Spain, and had been rescued from the entertainment and pet trades.

The researchers used a life-like android head, built with 33 servo motors, and capable of three facial conditions: yawning (mouth fully open to 5.5 cm or 2.17 inches), gaping (partially open to 1.5 cm or 0.59 inches), and closed-mouth neutrality.

Each condition lasted five minutes and was presented in a randomized order. The android performed each movement between 15 and 20 times.

Meanwhile, cameras recorded the chimpanzees’ reactions. The team also measured how much time the chimps spent looking at the android and lying down after each display.

Robots can make chimpanzees yawn

Yawning frequency surged only during and after the yawning condition. Chimps yawned 22 times during android yawns and 23 times in the post-yawn phase. That totaled 45 yawns – three times more than for any other facial condition.

No yawns occurred during the gaping or closed-mouth presentations. Only a handful of yawns were seen during baseline and post-close periods.

The response also extended to behavior. More chimps lay down after the android yawned, compared to after gape or closed-mouth conditions. They even gathered bedding materials – actions that were rarely seen during other conditions.

The results suggest that yawns from the android didn’t just mimic biology. They served as contextual cues for rest.

Yawns as social signals

“Our findings show that chimpanzees exhibit yawn contagion when triggered by a non-biological inanimate agent, a humanoid android, that looks as if it is yawning,” said lead author Dr. Ramiro Joly-Mascheroni.

“Despite its elusive primary functions – we still don’t know exactly why we yawn, let alone why yawning is contagious – yawning may still have an evolutionarily old, non-verbal communicative role, and its contagious aspect may help us find out more about how humans and animals developed ways of communication and social interaction.”

This extends earlier findings about contagious yawning in dogs, bonobos, and elephants. It implies that even without familiarity or biological cues, chimpanzees pick up and respond to socially meaningful movements.

Androids can help us study empathy

“Exploring the yawning responses of primates towards an artificial agent helps us to understand the mechanism of social cognition and interactions beyond humans,” said Professor Calvo-Merino.

“This interdisciplinary research enhances the collaboration of disciplines such as psychology, robotics and zoology.”

One interesting idea is that yawning may activate an embodied, perception-action coupling. The chimpanzees could be reacting automatically or making a deeper association – such as recognizing the android’s yawn as a signal to rest.

Instinctive yawn responses of chimps

The findings suggest that a living, biological presence is not essential to trigger yawning in chimpanzees. An artificial agent – a robot with human-like features – can produce the same contagious effect.

This challenges long-held assumptions that only animals or humans can evoke such deeply social and instinctive responses.

By showing that non-living entities can activate behaviors linked to empathy and relaxation, the study broadens the tools available for behavioral science.

Researchers can now design more controlled experiments without needing a live yawn source. This helps isolate which visual or motion cues are truly responsible for triggering social responses.

Implications of the research

The implications of the research extend beyond the yawning behavior of chimpanzees. Future studies might explore whether robotic agents can also provoke other reactions like mimicry, play gestures, or even emotional expressions.

Understanding which cues matter most could improve our knowledge of social cognition in both humans and animals.

Ultimately, the study shows that chimpanzees do not need skin, muscle, or familiar faces in order to respond. A plastic android, with carefully programmed movements, can be enough to signal rest.

The study is published in the journal Scientific Reports.

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