Yawns Help the Brain Keep Its Cool
Gallup says yawns have traditionally been known as a sign of sleepiness, or boredom. But recent evidence suggests that yawning may function to promote brain cooling.
The idea being, when you breathe in deeply, the incoming air slightly cools the brain. And stretching the jaw increases blood flow to the brain too–another cooling factor.
Reason we do it at night? “At night time when we’re about to go to sleep our brain and body temperatures are at their highest point throughout the day.”