Yawning

A yawn is a natural human reflex. It involves the inhalation of air, stretching of the eardrums, and is
followed by a large exhalation of
breath. Yawning is associated with tiredness, stress, lack of stimulation, and boredom. It is
one of the most bizarre human
functions. Yawning can be infectious and is triggered by
seeing others yawn, hearing a
yawn, or talking on the phone with someone who is yawning. A number of theories have been
proposed that attempt to explain why animals yawn, but nothing has been substantiated.

One theory states that yawning occurs
when a person’s blood contains
an increased amount of carbon dioxide and needs oxygen.
However, other studies show that
yawning decreases oxygen intake.
Another theory states that yawning is a person’s way of
controlling brain temperature. It
has been suggested that a yawn
can reduce or increase blood pressure in the brain. This theory
has been supported by the fact
that people get a desire to yawn
while making a drastic change in
elevation. Another speculated
reason for yawning is the desire
to stretch one’s muscles. Contagious yawning may be a
way of keeping a group of animals alert. It may be an
instinctual reaction from one member of the herd to the next,
reminding everyone to stay alert.
Anecdotal evidence suggests that
yawning helps increase the state
of alertness.