Yawning may keep us 'on the ball'
Yawning may appear the height of rudeness, but in fact your body is desperately trying to keep you awake, according to research from the US.
Psychologists who studied 44 students concluded that yawning sent cooler air to the brain, helping it to stay alert.
Yawning therefore delays sleep rather than promotes it, the study in Evolutionary Psychology suggested.
The desire to yawn when others do so may also be a mechanism to help a group stay alert in the face of danger.
The common wisdom is that people yawn because they need oxygen, but the researchers at the University of Albany in New York said their experiments showed that raising or lowering oxygen and carbon dioxide levels in the blood did not produce that reaction.
Their evidence suggested instead that drawing in air helps cool the brain and helps it work more effectively.