Why do we yawn?

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Why: Transformers: Revenge of the Fallen is 2 and a half hours long. Also, it started at 11 PM.

Answer: Nobody knows! Here are the facts:

• Yawning is an involuntary respiratory reflex.
• It's controlled by the spinal and nerve centers.
  
• It regulates oxygen and carbon dioxide levels in the blood.
• Seeing someone else yawn triggers a part of the brain called the superior temporal sulcus and deactivates the periamygdala region on the left side.

Here is the speculation:

• Yawning is triggered by fatigue or boredom. This is because at those times, breathing is shallow, and little oxygen is carried to the lungs.
• The sudden intake of oxygen increases the heart rate. This forces oxygen into the blood vessels in the brain and heightens alertness.
• Yawn contagion is unconscious - It bypasses the parts of the brain that makes us conciously analyze and mimic others.
• In early humans, yawn contagiousness might have helped people communicate their alertness levels to each other so they could coordinate sleep schedules.
  

Yawn right now. I command it!


Source: CoolQuiz, World-Science.net

The More You Know: More yawn facts:

• Yawning occurs excessively in patients with multiple sclerosis and damage to the lower brainstem.
• Fetuses in the womb yawn (even though they don't breathe oxygen til after live birth).
• Yawning is contagious in chimpanzees, too.