No one knows why we yawn. There are lots of theories, some talk about it signalling tiredness or getting oxygen to the brain, others mention clearing out stale air from the lungs and reducing blood carbon dioxide levels. 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.Technically, a yawn is the reflex opening of the mouth followed by the deep inhalation and slow exhalation of oxygen. you inhale oxygen and your body uses it up. The body makes a waste product called as carbon dioxide that is exhaled from the lungs when you breathe out. Scientists speculate that the onset of a yawn is triggered either by fatigue, or by sheer boredom as, at those times, breathing is shallow, and little oxygen is carried to the lungs by the oxygen-toting cardiovascular system. When you are sleepy, bored or tired, you breathe more slowly. Your body requires oxygen and needs to throw out the carbon dioxide. So, your brain makes you take an extra breath, which is deep and long called a yawn, so that you can take in more of oxygen and give out carbon dioxide fully. We know it's involuntary because we do it even before we are born. Research shows that 11-week-old fetuses yawn. when it is a well-known fact that they do not intake oxygen into their lungs until after live birth. Senju and colleagues from the University of Tokyo showed videos of people yawning or making mouth movements to 24 children with autism spectrum disorder and to 25 non-ASD children. Both groups of children yawned the same number of times while watching the video of general mouth movements, but the non-ASD children yawned more when watching the video of people yawning. Explains Senju, “Our study confirms the prediction of ‘empathy theory’, by demonstrating that individuals with autism. None of this answers the question of why do we yawn in the first place? The empathy angle perhaps points to an ancient benefit in group behaviour, but what that benefit is, science does not yet know.
