What makes us yawn?

Next time you're in a meeting, try this little experiment: Take a big yawn, cover your mouth out of courtesy, and watch and see how many people yawn. There's a good chance that you'll set off a chain reaction of yawns. Before you finish reading this, it's likely that you will yawn at least once. Don't misunderstand, i am not intending to bore you, but just reading about yawning will make you yawn, just as seeing or hearing someone else yawn makes us yawn.

While the dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function, and very little research has been done on the subject. However, there are several theories about why we yawn.