Next time you’re with a group of your friends, try this out. Take a big yawn, don’t forget to cover your mouth, and wait to see how many other people yawn. There's a good chance your yawn will be contagious. In fact, before you even finish reading this story it is likely that you’ll yawn at least once. Not that I’m trying to bore you, but just reading about yawning will make you yawn.
Yawning doesn’t always mean you are bored. Adelie penguins actually yawn as part of their wooing ritual. Couples face each other and the males stand with their beaks wide open and face towards the sky.
As for why people yawn... good question. Nobody really knows why we yawn. For a while scientists believed that you yawned when there was too much carbon dioxide and not enough oxygen in your blood. Part of your brain realized this and triggered you to yawn. As your mouth stretches you inhale deeply, sending a shot of oxygen to the lungs and into the bloodstream. That theory went out the window because nobody can prove it.
The reason yawns are contagious? Power of suggestion perhaps. If you’re out late with your friends after school, you're probably tired. You're probably on the verge of a yawn, too, and seeing one person do it is enough to drive everyone to yawns.
A Few Yawning Facts