Why Do We Yawn? A Biologist Explains (Hint: Most People Get It Wrong)

Scientists now think yawning is an ancient reflex tied to brain cooling and temperature regulation, not to boosting oxygen intake.

The old oxygen-and-carbon-dioxide theory has been rejected by experiments, despite its long history as a popular explanation.

New research points to a thermoregulatory role involving the hypothalamus and brainstem, which help keep brain temperature in check.

Experts say this reframes yawning as a brain-regulation behavior with evolutionary roots, rather than a simple breathing response.