Why do we yawn?

Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we're born. According to Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County, research has shown that 11-week-old feotuses yawn. And while yawning is commonly associated with relaxation and drowsiness, your heart rate can rise as much as 30 percent during a yawn, and yawning is a sign of arousal. Many parts of the body are in action when you yawn.

First, your mouth opens, and your jaw drops, allowing as much air as possible to be taken in. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex, and your diaphragm is pushed down. The air you breathe in expands the lungs to capacity and then some of the air is blown back out. So even though we still don't know for sure why we yawn, we do know lots of interesting things about yawning: you start yawning in utero; you yawn when you're aroused; more than half of you will yawn if you see someone else yawn; and reading about yawning makes you yawn!