Why do we yawn

Someone ask: Why do we yawn

Caveman say yawning happen when body and brain need a shift, like tribe stoking fire when camp feel dull. Science tribe still argue exact reason, but best idea say yawn help wake up brain, move blood and air a bit, and signal change from sleepy to alert or from bored to active. Yawn also spread in tribe, like one person striking flint and others soon catch fire; seeing or hearing yawn can make another yawn too. So yawn not just “need air.” It more like body’s big stretch for brain and face, a reset gesture. Cave wisdom: yawn is small thunder before body choose new state.