Despite being a universal human behaviour, no-one really knows much about yawning, other than it has something to do with boredom or sleepiness. Ironically, the topic can itself be all too dull, even for the few scientists attempting to study it. What must remain one of the most thorough but uninteresting of investigations, undertaken some years ago, was a Dr Carl Mayer who X-rayed numerous people attempting to yawn. Being thorough and methodical he also probed their throats with laryngeal mirrors and persistently palpated their necks. It all culminated in his confident claims that yawning could be divided into three precisely timed and distinct phases: “Initial inspiration”, taking between 1.9 and 4.3 seconds, “Acme”, lasting exactly 2.3 seconds, and “Expiration of 4.5 – 7.8 seconds duration. As to why we yawn, he dismissed it with two words – “cerebral fatigue”.
Astute physicians and scientists lost for an explanation for a phenomenon will often give it an impressive new name, usually derived from latin. For yawning, it’s ‘oscitation’ from ‘oscitare’ (to open the mouth wide). Added to this are ponderous and pointless explanations, for example, a well known medical textbook declared it to be, “a deep inspiration carried out with widely opened glottis, typically with open mouth, and frequently accompanied by movements of the arms etc… it is caused by certain psychic influences.”
The idea that yawning ‘aerates’ the lungs and increases the oxygen supply to the brain is nonsense, as breathing oxygen does not suppress the urge to yawn, and neither does carbon dioxide increase it. If anything, yawning leads to a fall in oxygen levels, as breathing usually ceases for a while after a yawn. There is little evidence that yawning wakes us up, as incidental findings from sleep clinics that happen to be measuring the EEG (‘brain waves’) of sleepy patients, show no changes to brain activity after a yawn. In contrast, yawning can also accompany stress and fear as, in the First World War it was commonly seen amongst troops in the trenches, waiting for the whistle to blow, ordering them to go ‘over the top’ and charge the enemy.
The Victorians had various theories, most of which can best be described as ‘imaginative’. For example, that yawning boosts alertness, as the widening lower jaw squeezes the thyroid gland, located in the neck below, to release more of its hormone, thyroxine, that increases body metabolism. Certainly, yawning causes a momentary increase in heart rate, but this is a reflex associated with any deep inspiration, and is followed by a slowing on expiration. Many early psychiatrists took a keen interest, with some strange concepts. For example, in patients with schizophrenia, yawning was seen as a good prognosis, supposedly to show that the patient wants to maintain contact with the real world.
The most recent ideas include keeping the brain cool, as it was found that sleepy people sitting with ice-packs on their foreheads were less susceptible to contagious yawning, which is hardly surprising considering how foolish participants must have felt.
Although yawning clearly has ‘something psychological about it’, surprisingly few psychologists have investigated it. One of the most entertaining accounts, was by Dr Joseph Moore from the George Peabody College, in Tennessee, who ran series of experiments in 1941. The first employed a stooge able to yawn at will, who sat in a nearby public library reading room, in full view of other readers. He yawned obtrusively every ten minutes whilst Moore sat unobtrusively in an overlooking gallery, recording the events in his notebook. Within a minute or so of each rendition almost half of the unwitting audience would follow suit. Another of Moore’s studies was more blatant, with a short movie of a girl yawning, shown to an unsuspecting audience, and soon followed by a doubling of the incidence of yawning among the onlookers. To determine whether yawning can be stimulated simply by hearing it rather than seeing the yawner, he played gramophone records of yawning to college students, with little response. But when played to blind students they yawned profusely.
As to why we cover our mouths when we yawn, is it embarrassment, or as it was thought by the ancient Greeks, to prevent one’s soul from leaving the body ? Although yawning and stretching are found in many mammals, contagious yawning has only been seen in chimpanzees.