Why do humans and animals yawn???

Question

Why do humans and animals yawn???

Answer 1

We have oxygen that runs throughout our circulatory system.  Whenever we are tired, or our circulatory system begins to slow down our brains do not receive enough oxygen.  Our brains then signal us to yawn.  The huge intake of oxygen when we yawn replaces what our brains are needing at that time.

Answer 2

To Cool the brain

Answer 3

They do it when they are tired so more oxygen can get to the brain to wake it up.

Answer 4

its a sign that you or they need oxygen to the brain.  so usually when your tired your not breathing properly and hense the yawn.  

Answer 5

We have oxygen that runs throughout our circulatory system. Whenever we are tired, or our circulatory system begins to slow down our brains do not receive enough oxygen. Our brains then signal us to yawn. The huge intake of oxygen when we yawn replaces what our brains are needing at that time.