Why do we yawn? It’s probably not because we’re bored. How often do you yawn because you’re bored?  We take in more oxygen when we yawn. Maybe we need more oxygen. I believe yawning was a signal we developed before we used language. It might have been a way to show our teeth before fighting. Have you ever noticed that you sometimes yawn when you’re nervous? I always thought I yawned before a test because I was tired after staying up all night. I thought I yawned before surgery while I was in residency because I had been on call the night before, and yet I wasn’t actually tired.…