Radiator cooling : When our bodies are hot, standing in front of a fan can be a quick fix, and the brain is the same way. When we yawn, we pull in cool air through the nasal and oral cavities, and that air comes in contact with all of the blood vessels in those densely packed areas. Many of those blood vessels carry blood directly to the brain, and the surge of air cools the blood, and thus the brain.
Catching a yawn : Why are yawns so contagious? Does the fact that we catch them from one another shed light on their underlying function? One possibility is that contagious yawning serves as a way of showing empathy. While all vertebrate mammals experience spontaneous yawning, only humans and our closest relatives, chimpanzees, seem to experience the contagion effect—a sign that there may be a deeper social meaning to the experience. What’s more, while spontaneous yawning occurs in the womb, contagious yawning develops only later in life, as does empathy. Children younger than five don’t yawn any more often when watching videos of yawns than they would normally.
Bigger brains mean longer yawns : Yawning—a stretching of the jaw, gaping of the mouth and long deep inhalation, followed by a shallow exhalation—may serve as a thermoregulatory mechanism, says Andrew Gallup, a psychology professor at SUNY College at Oneonta. In other words, it’s kind of like a radiator. In a 2007 study, Gallup found that holding hot or cold packs to the forehead influenced how often people yawned when they saw videos of others doing it. When participants held a warm pack to their forehead, they yawned 41 percent of the time. When they held a cold pack, the incidence of yawning dropped to 9 percent.
H/t to for asking this question
References and links