Why do we yawn?

"Scientist cannot explain why
every person on the planet
yawns – In most cases, several
times a day. Even babies in the
womb do it. So do hedgehogs,

ostriches, snakes and fish. There
are lots of theories, often
contradictory, but none satisfy all
the researchers. Many scientists
have proposed that an
explanation for this gulp of hair,
lasting six seconds on average, is
to augment the brains oxygen
supply. Yet "so far, researchers
haven't found evidence
supporting this suspicion," says
science news.
New studies on rats seem to
suggest that a "yawn may be a
thermostat, cooling an
overheated brain," But no one
really knows." – Awake magazine