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
BackWash.com and Columnist for bbc.co.uk h2g2 The Post where he
writes 'Not Scientific Science' column.
|
