Why do we yawn?

We yawn mainly because it may help the brain stay at a useful temperature and alertness level, especially when we are tired, waking up, or low on stimulation. It is probably not about needing extra oxygen, since studies have not shown a yawn raising oxygen in the blood.

The funniest part is how easily yawns spread. Seeing, hearing, or even thinking about one can set off the same action in another person. Scientists connect this to brain systems that copy and respond to other people's actions, which is why families can start yawning in a chain.