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?

Other science issues (not too complicated don't you worry)
can be found at:

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