Scientists still debate why yawning exists, and no single explanation is accepted.

The longer version

Several accounts compete: one says yawning cools the brain by drawing air across nasal and mouth tissues, another that it stretches jaw and throat muscles to keep them ready, another that it marks a transition between states of alertness. A fourth proposal treats it as a way to equalise pressure in the middle ear during altitude change.

None has carried the field, because each explains some observations and not others. Stretching accounts fail to explain contagion, and cooling accounts struggle with yawning that happens just before sleep. Textbook explanations often present one account as settled when the evidence is in fact mixed, and that is worth flagging. A behaviour this ordinary still lacks a settled explanation.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.