is being tired the only reason people yawn?
356917
No, as others said it has to do with the oxygen and carbon dioxide levels in your body. People who are not breathing properly (taking in too much oxygen & not letting enough cd out) can yawn or sigh constantly. Breathing through your nose is the best way to breathe (provided you have nothing wrong with your nose) and it should be like "breathe in 2...3 breathe out 2...3...4" it takes practice if you're used to mouth breathing, your brain will think you arn't getting enough air..but you are. Also yawns are catching...usually somebody saying the word will make nme yawn!!
164616
The exact reason is not known but there are a number of theories:\n\n1) Excess of carbon dioxide and lack of oxygen in the blood. The brain trieggers a yawn to expel carbon dioxide and inhale oxygen.\n2) Regulation of body temperature.\n3) An increase of certain neurotransmitters in the brain, specifically serotonin, dopamine, glutamic acid and nitric oxide.\n4) A yawn is similar to stretching in that it increases blood pressure and heart rate and also flexes many muscles and joints.
64755
Personally, I think it's a sub-conscience action since you don't have to be aware of someone else yawning. Think of it this way, you weren't hungry until you saw, smelled, or someone mentioned food. So as you idle your body equates lack of action as rest. As we all know, rest is equated to sleep, so your idle body wasn't tired until someone yawned. \n\nI know it sounds odd but, have you ever yawned while your cardio system was working harder than compared to sitting idle?
467214
Yawns are one of the brain's ways of getting oxygen and fighting fatigue. If someone yawns in response to your yawn it's because they are feeling the same fatigue you are.
346467
Yawns are not contagious, its an urban legend. Watch 'Mythbusters' on the Discovery channel.
1170939
From what I've read, we are not sure exactly why that happens, but many doctors and scientist believe is is due to a mental reaction that sees a person yawn and believes you should do so as well.  Yawning is a response to a lack of oxygen in the brain under idle conditions, such as standing around or sitting in a chair.  So when you see someone yawn, your brain triggers a yawn to make sure you are also not starving your brain.
607567
Urge to yawn on seeing someone else yawn is called reflex yawning. When you see someone else yawn, it sends a message across your brain that you also need more oxygen and as a response your open your mouth wide in an attempt to get in more air and your lungs expand (i.e you yawn).
814479
Yawn.....................
775112
It's a sympathetic reaction that makes them contagious.  A yawn happens when your body is not receiving enough oxygen.  You yawn when someone else yawns because of this sympathetic reaction.  Mythbusters did an experiment on this topic on one of their shows.
321997
Cause when you yawn, you are thought to release carbon dioxide, and when somebody else gets the carbon dioxide, then they have to release it.  Another theory is, a long time ago when humans first existed, it meant it was time to go to sleep, so everyone would know toy go to sleep.  Isn't that so cute?  ^.^
481912
scientifically it's because your body forces an action to acquire something, in this case it's OXYGEN. breathe deeper or more constantly. try it. if you breathe like about a quarter of your max breathe every 5 seconds you will yawn after a while.
262175
science are baffled why yawning is contagious. They have none whatsoever for explaining this phenomena. However psychologies insists it is psychological.
410453
we yawn b/c our body is craving more oxygen.. this is fact
480001
Virtually any stimulus associated with yawns -- including viewing, reading about, and even thinking about, yawning -- evokes yawns. (Are you yawning yet?) Yawning spreads in a chain reaction through a group, a compelling example of human herd behavior and a reminder that we are not always in conscious control of our actions. The urge to replicate an observed yawn is clearly an automatic response triggered by our brains.
198710
When you yawn, you are attempting to take in as much air as possible, more oxygen gives more energy.  People in the immediate area are in competition for this air too and yawn as a response to retrieve air themselves
272413
It is an instinctual social response.  Yawning signals to others in the social group that it is time to rest.
375489
Virtually any stimulus associated with yawns -- including viewing, reading about, and even thinking about, yawning -- evokes yawns. (Are you yawning yet?) Yawning spreads in a chain reaction through a group, a compelling example of human herd behavior and a reminder that we are not always in conscious control of our actions. The urge to replicate an observed yawn is clearly an automatic response triggered by our brains.\n\nStudies partially explain the reason for yawning. Although we yawn more when sleepy or bored, it is unclear whether yawning increases alertness. And scientific evidence refutes one of the most popular myths of yawning? that it happens in response to low oxygen or high carbon dioxide levels in the blood or brain. Test subjects do not yawn more when breathing air with enhanced levels of carbon dioxide nor do they yawn less when breathing pure oxygen. One fact explains a lot of apparently inconsistent data. People yawn most during behavioral transitions, such as just after waking and shortly before bedtime. Yawning may help facilitate those changes. Contagious yawning may synchronize a group's behavior so that, for instance, a whole family goes to sleep together.