Saturday, March 08, 2008

Is yawning contagious?

Author: Khalil A. Cassimally

It is a fact to any observer that yawning flies like a butterfly and stings like a bee. Scientists and others studying yawning, seem to have reached that same conclusion. Yawning is indeed contagious. But why?

Yawning is thought to be a reflex act of opening one's mouth wide and inhaling due to an increase of carbon dioxide in the bloodstream. By inhaling deeply – during yawning that is – a large amount of oxygen is breathed in and the accumulated carbon dioxide is expelled. Yawning usually occurs when one is bored or tired. During these periods of time, one's breathing rate slows and this has as consequence to increase the carbon dioxide concentration in the bloodstream. An average yawn has duration of 6 seconds and this does have a significant effect to the heart rate, and thus the distribution and expelling of oxygen and carbon dioxide respectively. The heart rate in fact increases on average by 30% during yawning.

However to answer the question of "why yawning is contagious," three leading theories have been put forward namely the physiology theory, the boredom theory and the evolutionary theory.

The physiology theory proposes that the infectious nature of yawning occurs as a result of an involuntary realisation that a deep intake and belching of oxygen and carbon dioxide respectively are needed. When Guy A sees Guy B yawn, it is a reminder to Guy A that he too may be feeling the lack of oxygen and this consequently makes Guy A to yawn as well.

The second theory – and possibly the most entertaining one – states that yawning is simply a way of showing others or ourselves that something is mundane or boring. But in this theory, yawning is not really contagious. Instead other people yawn because they too find that same thing mundane or boring rather than depending on one person to spread the yawns. However if the interviewed people found something dull, chances are that the others found it equally tedious. Therefore everybody opens his mouth wide and inhales some oxygen.

The third theory – which is the most appealing to me personally – is the evolutionary theory. According to this theory, yawning is a behaviour started by our ancestors, the cavemen. This theory puts forward that yawning was a sort of social signal to others. Therefore when one yawns, the others yawn back to return the call. This behaviour thus persists even today, according to the evolutionary theory, but it has faded away much. This explains why about 55% of people who see somebody else yawn will do too so as well within the following 5min.

In humans, the earliest yawns occur before a baby is born, in the mother's womb, only 11 weeks after conception. This clearly seems to show that yawning is a reflex action above all. Those 3 other theories are pure suppositions up till now and have not been proven by any scientific study even empirically.

Also all 3 theories have major pitfalls. The most eye-catching one applies to the first theory, the physiology theory, which proposes that yawning occurs due to accumulation of carbon dioxide in the body and lack of oxygen. Studies have shown that receiving additional oxygen didn't decrease yawning and people exposed to a lower amount of carbon dioxide didn't stop yawning.

For the boredom theory, well, I am pretty sure that out of those people who do not regularly visit art galleries, only a fraction will yawn and yawn on their first visit to expositions even if they find the stuff boring.

The third theory seems to walk its way to the why of yawning, on playing cards. The evolutionary theory can easily crumble because we do not know whether cavemen were yawning first and foremost. As the theory builds itself on a very debatable fact, it may easily collapse.

For now though, I'll keep my mouth wide shut. But by the way, how many times did you yawn while reading this column?

About the author: Khalil A. Cassimally is currently Senior Columnist at and Columnist for h2g2 The Post where he writes 'Not Scientific Science' column.


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