via spring.org.uk
Err, don't people yawn because they're bored and/or tired? Yes, it's true people do yawn more at bedtime or after they've woken up and they do yawn when they're bored (people even yawn in their sleep).
But yawning isn't that simple. If it was, how could you explain that some paratroopers yawn before their first jump, as do some violinists before they go on stage and Olympic athletes before their event (Provine, 2005). These are hardly situations in which people are likely to be bored.
Many people believe that yawning gets more oxygen into the body or expels more carbon dioxide. But this is not true. The theory is now thought to be seriously flawed, if not plain wrong.
The truth is no one really knows the real root cause of a yawn. Some good guesses have been made, though, and it's likely that some combination of them is true. First let's look at the physiological, before we get onto the psychological.
