You know the feeling. It’s getting close to bedtime, you get sleepy, and you start yawning automatically. You may even find yourself yawning in the middle of the day in a mid-day lull. These yawns ...

Humans aren't alone when it comes to yawning — all vertebrates do it too, including fish, amphibians, reptiles, birds and mammals. But why? The "evolutionarily ancient" act of yawning likely serves a ...