Why is yawning contagious?
Sure, there's no hard and fast reason why it's contagious. It may remain one of those mysteries, like how to cure the hiccups. But there are several theories.
First mentioned is that it's a method of cooling the brain, to help stay alert and detect danger. So, before you get into a fist fight, try yawning to cool down your brain (hey, who knows, maybe with a cooler brain you'll start thinking more clearly) and give you an edge up on the competition. Just don't let them see you yawn, or they'll do it too and you're leg up will instantly become a level playing field.
Yawning might help maintain vigilance, especially in groups. Does this mean that in my next business meeting, I can yawn openly and widely, and tell my boss that it's a compliment, because I was making sure I remained vigilant in the meeting? On an unconscious level, we realize that our attention is wandering, we're not paying as much mental attention as we should to the task at hand. So we start yawning, not as a means of displaying how tired we are, but as a way to bring our attention back on target.
It would be interesting to know how many times I yawned while typing this post. It didn't occur to me to count until halfway in. How many times did you yawn while reading it, and the article?