So I recently found out the science of yawning and I think the reasoning for it is so interesting, that I figured I'd share it with everyone else. To keep it short and sweet: we yawn to keep our brains from overheating. Stretching your jaw while yawning gets the blood flowing and changes in circulation affect the rate of blood flow and the temperature of blood coming to the brain. Also as you all know, yawning can be contagious. So if anyone asks Why do we yawn? just tell them it stops our brains from getting too hot.