Why do people yawn ??

to get more oxygen and also to indicate they r sleepy

The standard theories. 1. Yawning is induced by hypoxia (low oxygen levels in the blood stream). The idea behind this (the most popular) theory is that yawning causes you to take a deep breath when you need some extra oxygen - perhaps because you are tired are have not been breathing enough. These are MANY problems with this idea, but the main problem is that yawning occurs only when you are tired and does not occur in the many other instances of hypoxia. For example, if you exercise hard you need more oxygen - but your body makes you breath harder, not yawn! If you are brought from, say, sea-level to an elevation of 20,000 feet within a time period of 5 min, you will immediately faint due to severe hypoxia, but you will not yawn. 2. Yawning is a method for communicating to other individuals your physiological state of being tired. This idea is that several human behaviors are for communication purposes. Thus, smiling is to let people know that you're happy, crying is to tell people that you are very sad (and possibly need help), the facial expressions of anger and to let people know that you are mad, and yawning is simply to let people know that you're tired. The problem with this idea is that nearly all vertebrates yawn, including fish, alligators, turtles, etc. Yet it is hard to believe that your goldfish is trying to communicate its feelings or tiredness! These lower vertebrates don't show any other "feeling" communication behaviors (such as smiling, purring, crying, etc.) Thus it does not seem likely that they yawn as a communication device. This does not mean that humans don't use yawning to communicate feelings, but yawning certainly didn't originate for this reason. 3. Yawning is used to stretch out the lungs to prepare them for use. Perhaps the lungs need a little stretching every once in a while to get out the wrinkles, etc. This would explain why yawning is often associated with stretching other muscles (like the arms, etc.) So all you are doing is preparing the body for a hard day of work. However, this would not explain why you yawn when you get tired before bed - because sleeping definitely does not qualify as a "hard day of work." You don't need to prepare you lungs for sleep since sleep requires much less oxygen than being awake.

When people are tired and feel sleepy they yawn that's my personal experience.

No scientific explanation for it. When people are bored or tired they yawn.

yes a yawn is nothing more than your body trying to get more oxygen to the brain

It has a biological reason. Our bodies induce yawning to draw in more oxygen or remove a build-up of carbon dioxide. When the air passage above the nasal chamber gets blocked due to the pressure then you have to yawn to release your blocked air else it will lead to hiccups. Its a natural tendency and thats why it causes tension on your eyes after you yawn. Here are some facts for you: The average yawn lasts about six seconds. Your heart rate can rise as much as 30 percent during a yawn. 55 percent of people will yawn within five minutes of seeing someone else yawn. Blind people yawn more after hearing an audio tape of people yawning. Reading about yawning will make you yawn. -- So look at you as you are yawning now.

People yawn to get more oxygen to their brain.

I agree with sedel too

From Wikipedia, the free encyclopedia For other uses, see Yawn (disambiguation). g A yawn (synonyms chasma, oscitation from the Latin verb oscitare, to open the mouth wide[1]) is a reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from lack of stimulation. Pandiculation is the term for the act of stretching and yawning. Yawning is a powerful non-verbal message with several possible meanings, depending on the circumstances. It is also claimed to help increase the state of alertness of a person. The exact causes of yawning are still unknown. Here's the link fro more: http://en.wikipedia.org/wiki/Yawn

From Wikipedia, the free encyclopedia For other uses, see Yawn (disambiguation). g A yawn (synonyms chasma, oscitation from the Latin verb oscitare, to open the mouth wide[1]) is a reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from lack of stimulation. Pandiculation is the term for the act of stretching and yawning. Yawning is a powerful non-verbal message with several possible meanings, depending on the circumstances. It is also claimed to help increase the state of alertness of a person. The exact causes of yawning are still unknown. Here's the link fro more: http://en.wikipedia.org/wiki/Yawn

to get oxygen to there diaphram. yawns are highly contagious. even if you stare a a cat and yawn they will yawn too!