Health and the human body - Psychology & behavior - Yawning
Which common explanation for why humans yawn has not been scientifically confirmed?
Correct!
People yawn for several possible reasons, including tiredness, shifts in attention, and perhaps regulation of brain temperature. However, the common assumption that yawning mainly increases blood oxygen or removes carbon dioxide has not been confirmed. In experiments, neither pure oxygen nor elevated carbon dioxide significantly changed yawning frequency. The exact function of yawning is still not fully understood.
Source: PubMed, Provine et al.
