Everybody yawns
— from unborn babies to the oldest great-grandparent. Animals do it,
too. But why, exactly, do people and animals yawn? No one knows for
sure. But there are many theories (ideas) about why people yawn.
One is that when we are
bored or tired, we just don't breathe as deeply as we usually do. As this
theory goes, our bodies take in less oxygen because our breathing has slowed.
Therefore, yawning helps us bring more oxygen into the blood and
move more carbon dioxide out of the blood.
Yawning is an involuntary reflex
(something we can't really control) to help us control our oxygen and carbon
dioxide levels.
Other studies
have shown that breathing in more oxygen and also breathing in more carbon dioxide does not increase yawning.
Another theory is that yawning
stretches the lungs and lung tissue. Stretching and yawning may be a way
to flex muscles and joints, increase heart rate, and feel more awake.
Other people believe that
yawning is a protective reflex to redistribute the oil-like substance called
surfactant that helps keep lungs lubricated inside and keeps them from
collapsing. So, if we didn't yawn, according to this theory, taking a deep
breath would become harder and harder — and that would not be good!
But there is one idea about
yawning that everyone knows to be true. It seems contagious. If you yawn in class,
you'll probably notice a few other people will start yawning, too. Even
thinking about yawning can get you yawning. How many times have you yawned
while reading this article? It seems to be psychological too!
