Simply reading or even thinking about the word 'yawn' can trigger the act in many people. This phenomenon is real and has been named by researchers as yawn contagion, occurring because the brain processes the mere idea of yawning similarly to observing someone yawning in person.
Science is still seeking to understand the underlying reasons: why we yawn initially, and why this behavior spreads among individuals and even across different species so easily. Currently, there is no definitive consensus on any of these issues.
Two main theories compete to explain the biological function of yawning, while a third line of investigation attempts to elucidate its contagious nature, linking it to empathy and social proximity, that is, the ability to put oneself in another's place.
Hypotheses on the Biological Function of Yawning
One of the best-known ideas is the brain cooling theory. According to it, yawning—characterized by a deep inhalation followed by a wide opening of the jaw—serves to increase the flow of air and blood to the head region, helping to reduce brain temperature when it operates less efficiently, such as during sleep or boredom.
A 2014 study involving biologist Andrew Gallup from the American university SUNY Oneonta established a correlation between a higher frequency of yawns and warmer environments.
The second hypothesis considers yawning as a regulator of the state of alertness. From this perspective, yawning helps the brain transition between different levels of wakefulness, whether upon waking up, before sleeping, or when moving from a state of boredom to an activity requiring attention. It is important to note that these two explanations are not mutually exclusive; a yawn can simultaneously cool the brain and indicate a change in the state of alertness, although neither has reached the status of final consensus.
The Contagious Aspect of Yawning
The transmissible aspect of yawning is analyzed separately from its biological function. One of the most frequently cited results comes from researchers at the University of Pisa, Italy, in 2011. They observed that the probability of a person 'catching' another person's yawn increases proportionally to the degree of social bond between them: relatives transmit more than friends, who transmit more than acquaintances, and these, in turn, more than strangers.
The most accepted interpretation suggests that contagion acts as automatic social synchronization, being linked to the same neural network used to recognize and mirror the emotional state of those nearby.
However, this connection to empathy is debated. Certain experiments conducted with individuals on the autism spectrum reported lower contagion rates, which reinforced the hypothesis of a direct link between contagious yawning and empathy. Nevertheless, other studies have failed to replicate this finding, indicating that the relationship is not yet unanimous among area specialists.
Contagion also demonstrates the ability to cross species. A study by British researchers, published in the journal Biology Letters in 2008, demonstrated that dogs yawned more frequently after observing or hearing a human yawn. At that time, this was interpreted as proof of empathetic bonds between dogs and their owners.
Subsequent research, however, questioned this conclusion: some could not reproduce the effect, and others suggested that canine yawning in these circumstances might be more related to stress or an automatic reaction to a stimulus, rather than primarily to empathy.
This places the science of yawning at a fascinating point: there is concrete data proving the existence and spread of the phenomenon, but the explanations for why remain competing.