Is this really why we yawn?


Dec 02, 2014 by British Blog

In 1923, British neurologist Sir Francis Walshe noticed that when some of his paralysed patients yawned, they regained motor function for as long as the yawn lasted. This led Walshe to conclude that yawning was a strange phenomenon, outside the realm of human control - and indeed the question of why we yawn remains, although various ideas have been put forward over the years.


Social signals?

Some have claimed, for example, that yawning is an instinctive behaviour, intended to intimidate others by showing the teeth. Still others suggest that the 'contagious' nature of yawning (around 50% of humans - and chimpanzees - find themselves yawning when they see others do so, or even if they just hear or read about yawning) reveals it to be a form of social signalling, perhaps a way of telling other community members that it is time to become alert.

Other claims include that yawning is a way of drawing extra oxygen into the body, but studies do not support this, there is little evidence to show that yawning affects the body's oxygen levels, blood pressure or heart rate in any sustained way. Furthermore, if yawning was nature's way to draw more oxygen into the body then it would be reasonable to expect increased yawning to occur during exercise, but this does not seem to be the case.


Temperature control

Most recently, scientists have claimed that yawning is actually a temperature control mechanism for the brain and there does seem to be evidence to support this.

The human brain is extremely sensitive to temperature, and works most efficiently when it is cool. The new theory suggests that when we yawn, we draw in air that is at a slighter lower temperature than our bodies, and that the characteristic jaw movements involved in yawning cause the air to be drawn up through the sinuses, which flex in such a way that they force the cool air upwards across the brain, cooling it. Thus cooled, the brain becomes more alert and effective.

Studies conducted on rats do show that yawning lowers brain temperature, while other research using mice has shown that yawning is generally preceded by an increase in brain temperature.

The temperature control concept may also explain why we seem to yawn when we feel tired and just before we sleep. Humans experience a drop in brain temperature just before the onset of sleep, so if yawning does cool the brain it could facilitate that process. It might also act as a signal - to the individual or to the community - that the time to sleep is imminent.

Interestingly, in 400 BC, Hippocrates (the Ancient Greek doctor considered to be one of the most important figures in the history of medicine) speculated that yawning might be related to fever, in much the way that boiling water lets off steam.



While the temperature control concept seems to be gathering widespread support, as things stand, nobody can explain with certainty why we yawn. Perhaps yawning fulfils a variety of purposes, including social signalling within a community (interestingly, we are more likely to 'catch' yawning from people we are emotionally close to), as well as for physiological reasons. Clearly, more research is needed before we know for sure.