Why do people yawn?

            Yawning is an involuntary action, which causes us to open our mouths wide and breathe in deeply. It is called an involuntary action, as we do yawn even when we are still in our mother's womb. According to some research, a fetus as young as 11 weeks old can yawn. There are a number of theories associated with what causes a yawn.
           Physiological Theory: According to this theory, our body induces yawning to draw in more oxygen into the body and remove the build-up of carbon dioxide. This is precisely the reason, why we yawn more often, when we are sitting in a large group, as a large group produces more carbon dioxide. Our bodies try to get rid of carbon dioxide, by drawing in more oxygen. You may want to read more on lack of oxygen to the brain.
          Cooling of Brain Theory: There are some studies, which point to the fact, that yawning cools the brain, when it is overheated. The brain is able to function at its best, when it is cool and humans and other animals have evolved adaptations to accommodate this.
          Evolution Theory: There is a line of thought, according to which, our ancestors started yawning, so that the teeth could be visible and the others can be intimidated. There is an offshoot of this theory as well. According to this new theory, yawning developed from early man as a signal for us to bring about a change in activities, which are currently being carried out. If one has to talk about it evolutionarily, it was a way of maintaining vigilance or alertness.
         Boredom Theory: According to some of the dictionaries, yawning is caused due to boredom, fatigue or drowsiness. It can be taken as a sign to change the current activities. On a lighter note, no wonder we yawn that much during lectures *yawn*.


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