Almost everyone yawns when they feel sleepy. So do most animals.But we don’t completely understand why people and animals for that matter, yawn.
It’s widely assumed that yawning occurs because we are tired or bored or because we see someone else doing it, but there isn’t any hard evidence to support these beliefs.
Scientists do not purport to know all of the biological mechanisms of the yawn, but tend to agree that a yawn is an involuntary respiratory reflex, which regulates the carbon dioxide and oxygen levels in the blood. Read more…
