The Science of Yawning
How and why we yawn still presents problems for researchers in an area only recently opened up to study
Y awning is among the most familiar of all human behaviours, yet it was largely ignored by science until the final decades of the twentieth century. When the neuroscientist Robert Provine began studying yawning systematically in the 1980s, he found it surprisingly difficult to persuade fellow researchers that the phenomenon merited serious investigation. The reluctance was understandable: yawning appeared too trivial, too universal, and too obvious to warrant dedicated study. Provine's persistence eventually demonstrated that this apparent simplicity was illusory.
Provine's initial work focused on establishing the precise physical characteristics of the yawn. He recorded hundreds of yawns by asking volunteers to think about yawning -- a reliable technique for inducing the response -- and to press a button the moment a yawn began, releasing it at the moment of exhalation. The resulting data revealed that a typical yawn lasts approximately six seconds from the moment of jaw opening to final exhalation, though individual yawns ranged from about three seconds to considerably longer. The duration showed no reliable relationship to how frequently a person yawned: those who produced longer yawns did not compensate by yawning less often, and vice versa.
What most struck Provine about the yawn was its resistance to interruption. Once a yawn begins, it proceeds to completion with a kind of physiological inevitability that he compared to a sneeze -- another reflex-like action that, once initiated, cannot easily be stopped. Unlike a true reflex, however, which is a fast, proportional response to a specific stimulus, yawning is an extended, stereotyped action that ethologists classify as a fixed action pattern. Provine demonstrated this through a series of experiments in which volunteers were asked to yawn while simultaneously clenching their teeth or pinching their nostrils closed. Clenching the teeth, which prevented the jaw from opening fully, reliably produced the uncomfortable sensation of a yawn that could not reach completion -- evidence that the full gaping of the jaws is an essential component of the action sequence. Blocking the nostrils, by contrast, had no effect on the yawn's course, confirming that nasal breathing is not required.
Beyond the jaw and airway, yawning involves a surprisingly wide range of bodily systems. A fully expressed yawn typically includes backward tilting of the head, stretching of the facial muscles, narrowing or complete closure of the eyes, increased tear production, salivation, and changes in the Eustachian tubes of the middle ear. These accompanying features led Provine to suggest that yawning might be best understood not as a discrete act but as part of a broader motor complex that includes stretching. The connection between the two actions had been noted in clinical contexts as far back as the 1920s, when the British neurologist Sir Francis Walshe observed that patients paralysed on one side of their body following a stroke would, on yawning, experience involuntary movement in the otherwise immobile limb.
The contagious quality of yawning -- the fact that witnessing another person yawn, reading about yawning, or even thinking about it can trigger the response -- has attracted considerable research interest. Studies have found that contagious yawning is more common among individuals who score highly on measures of empathy, and that it appears to be absent in very young children and in individuals with certain neurodevelopmental conditions. This pattern has led some researchers to propose that yawning may play a role in social bonding or the synchronisation of group behaviour, though this interpretation remains controversial.
Despite decades of research, the question of why we yawn remains unresolved. Many popular explanations -- including the once widespread belief that yawning supplies the brain with additional oxygen -- have been tested and rejected. Provine himself concluded that yawning is probably associated with transitions between behavioural states, occurring most frequently at moments when an individual is shifting from one level of alertness or activity to another. If this is correct, yawning may be less a response to any single internal condition than a marker of the brain's ongoing regulation of its own level of engagement with the world.