Why do people (Humans) yawn?
410453
we yawn b/c our body is craving more oxygen.. this is fact
394382
Yawns are contagious because people naturally emulate what they see others doing. For more, read a section in the Tipping Point by Malcom Gladwell.
632459
Causes of yawning\n1.An indication of tiredness, stress, over-work or boredom. \n2.An action indicating psychological decompression after a state of high alert. \n3.A means of expressing powerful emotions like anger, rejection or apathy. \n4.A sign that one is not breathing deeply, and not receiving enough oxygen through the body. \nA yawn can express strong anti-social messages, and so in some cultures people try to mute or mask them by placing a concealing hand over the yawning mouth.\n\nA long-standing hypothesis is that yawning is caused by an excess of carbon dioxide and lack of oxygen in the blood. The brain stem detects this and triggers the yawn reflex. The mouth stretches wide and the lungs inhale deeply, bringing oxygen into the lungs and hence to the bloodstream. It is almost certain however, that this hypothesis is not correct. One study documented that this effect does not exist ("Yawning" by Robert R. Provine, pages 532-539, American Scientist, November-December 2005, Vol 93, No. 6). A more recent hypothesis is that yawning is used for regulation of body temperature. Another hypothesis is that yawns are caused by the same chemicals (neurotransmitters) in the brain that affect emotions, mood, appetite and other phenomena. These chemicals include serotonin, dopamine, glutamic acid and nitric oxide. As more of these compounds are activated in the brain, the frequency of yawning increases. Conversely, a greater presence in the brain of opiate neurotransmitters such as endorphins, reduces the frequency of yawning. Patients taking the serotonin reuptake inhibitor Paxil (Paroxetine HCl) have been observed yawning abnormally often.\n\nAnother theory is that yawning is similar to stretching. Yawning, like stretching, increases blood pressure and heart rate while also flexing many muscles and joints. Some have observed that if you try to stifle or prevent a yawn by clenching your jaws shut, the yawn is unsatisfying. As such, the stretching of jaw and face muscles seems to be necessary for a good yawn.\n\nThe yawn reflex is often described as contagious: if one person yawns, this will cause another person to "sympathetically" yawn.[2] The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.[3] Other theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon. It signals tiredness to other members of the group in order to synchronize sleeping patterns and periods of activity. It can serve as a warning in displaying large, canine teeth, thus proclaiming, "don't attack while I am sleeping..." The contagion of yawning is interspecific (i.e., try yawning in front of your dog). Yawning in public is generally regarded as impolite in the West, but came into fashion in polite French society for a brief period in the late 18th century. Oddly, sometimes sympathetic yawning may be caused by simply looking at a picture of a person or animal yawning, or even seeing the word "yawn".\n\nAdelie Penguins employ yawning as part of their courtship ritual. Penguin couples face off and the males engage in what is described as an "ecstatic display," their beaks open wide and their faces pointed skyward.
977252
From Wikipedia:\n\n"A previous long-standing hypothesis is that yawning is caused by an excess of carbon dioxide and lack of oxygen in the blood. The brain stem detects this and triggers the yawn reflex. The mouth stretches wide and the lungs inhale deeply, bringing oxygen into the lungs and hence to the bloodstream. It is almost certain, however, that this hypothesis is not correct. One study has documented that this effect does not exist."\n\nGoes on to newer, updated theories.\n\nAlso:\n\n"The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct. Other theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon."\n\nGoes on to give other reasons for contagion. <Yawn!> Enough!
202412
THE TRUTH IS that we don’t completely understand why people, or animals for that matter, yawn. It’s widely assumed that yawning occurs because we are tired or bored or because we see someone else doing it, but there isn’t any hard evidence to support these beliefs.\n\nThe most plausible explanation, and the one that is taught in medical school, is that we yawn because oxygen levels in our lungs are low. \n\nStudies have shown that during normal, at-rest breathing, we don’t use anywhere near our lung capacity; for the most part, we just use the air sacs at the bottom of the lungs. If the air sacs, called alveoli, don’t get fresh air, they partially collapse and the lungs stiffen a bit. As a result, it’s believed, our brain prompts the body to either sigh or take a yawn to get more air into the lungs.\n\nBut certain aspects of yawning remain even more mysterious. Fetuses, for instances, have been observed yawning in the womb, yet it’s known that they don’t take oxygen in through their lungs. And yawning seems to be a symptom of multiple sclerosis and other medical conditions, for reasons unclear.\n\nAnother puzzling phenomenon is that some male animals, men included, yawn in association with penile erection (although it’s presumptuous to assume they’re bored with their sex lives).
307772
Just a guess...  When you yawn, you take in more air than normal.  This means you get more oxygen than normal.  In a situation where it might be important to get more oxygen than your normal breathing urge will provide, an animal that yawns will have an advantage over one that doesn't yawn.  Since there is no disadvantage to yawning and occassionally there is an advantage, a mutation that causes an animal to yawn in response to another yawn would be passed on.
309172
padillio is right. it is just a mental thing, and she is also right in saying that it is because of a lack of oxygen. it is also associated with being tired b/c when you're body is fatigued or tired, you're breathing slows down and you get a lack of oxygen. yawning is an involuntary muscle movement to make you breath heavily and take in more oxygen. anyway, that's pretty much it.
522649
Prehistoric hunter gatherers had to face many threats, from big predators to neighbouring tribes.\n\nOne theory (and it's just a theory, mind, no one knows for sure) is that yawning might have evolved as a way of drawing attention to the fact that the guy on watch was getting sleepy.\n\nThe guard yawns involuntarily, the other hunters in the group might not notice it consciously, but subconsciously they do, and they pass it on. Eventually someone notices that the group is tired and goes to checks on the the guy on watch.\n\nI like this theory, it makes sense to me.
422922
It is also believed to be linked to social bonding.\n\nExperiments with chimps have shown that they also yawn when another chimp yawns.  Also videos (night video) in caves, where there is no light, where a certain species of monkey sleep - shows that they all yawn audibly before going to sleep.  Kind of a way of letting everyone know that they're there, even though they can't see each other.\n\nThis has probably carried through to humans.\n\nHave a look at http://www.theanswerbank.co.uk/Science/Question117042.html\n\nor\nhttp://webperso.easyconnect.fr/baillement/contagion-platek.html
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.
56869
The answer is, no one really knows why yawning is "contagious". Or why we yawn at all. One popular explanation is that yawning allows you to get rid of too much carbon dioxide in your system and increase your oxygen supply. This was disproved by Dr. Robert Provine and his research team in 1987.\n\nNow scientists are wondering if yawning is from our deep past -- part of our evolutionary history. Did a yawn signal to the group that it was time for everyone to retire to the trees and snooze? Did a yawn signal that we were all feeling cozy and warm about each other? Did a yawn signal something more like, "Gee, I know how you're feeling, I feel that way too."
406589
One theory says that it is a vestige of the group behavioural aspect of human evolution. This theory was put forth following observations of communal yawning in apes. The leader in an ape group yawns, and the rest follow suit. \n\nApart from the theories, consider this: \nTo some extent, yawning is indicative of one's state of mind, and can be physiologically linked to cerebral activity. It usually comes when all novelty in an idea or concept being explored has been temporarily exhausted. So it may happen that when an idea is being explored in a group, a statistical majority would always hit a 'low' (or an intellectually lean) patch in the exploration simultaneously . Hence yawning results. \n\nThe other type of yawning is when there is no group activity involved, and one yawns just by looking at another person yawning. This has to do with empathizing, as has been explained.
260771
we yawn when we get bored and it is very embarrsing esp. in public places,with me once they start they go on and on. maybe you idnt check yourself form childhood and now its a habit. force yourself to stop opening the mouth you will gradually overcome it.
56870
The dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function, and very little research has been done on the subject. However, there are several theories about why we yawn.\nThe Physiological Theory -- Our bodies induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. However, if our bodies make us yawn to drawn in needed oxygen, wouldn't we yawn during exercise? Robert Provine, a psychologist at the University of Maryland, Baltimore County, and a leading expert on yawning, has tested this theory. Giving people additional oxygen didn't decrease yawning and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning. \nThe Evolution Theory -- Some think that yawning is something that began with our ancestors, who used yawning to show their teeth and intimidate others. An offshoot of this theory is the idea that yawning developed from early man as a signal for us to change activities. \nThe Boredom Theory -- In the dictionary, yawning is said to be caused by boredom, fatigue or drowsiness. Although we do tend to yawn when bored or tired.
318834
Sociologist and Psychologists point to the fact the humans are usually very empathetic. That is they relate to and understand the things that other humans do to the extent of which they can even experience similar feelings. Like watching a porno turns people on, or seeing someone cry makes you concerned or even sad, the same applies to yawning. People are visually stimulated by what they see, and the brain makes an association between what they are seeing and their own experiences. In this way seeing someone yawn triggers your brain to look for information relating to what youre seeing, and oh it finds that yawning is related to the feeling of sleepiness, you process this information and decide to yawn too! =)\n\nBy the way the thing people are saying about signaling the tribe to sleep is off. Humans are by nature, empathetic. For example if someone laughs, you want to laugh too.\n\n\n(Please be sure to chose the best answer after 24 hours! Do not just leave the questions OPEN! Thanks)
378590
People yawn when the level of carbon dioxide in their blood is a little too high, this is bad and eventually can cause unconsciousness.  To stop this you yawn, yawning means you take in a big gulp of oxygen and expel carbon dioxide.  They are thought to be contagious because if I see you yawning my brain thinks.. uh oh there is too much carbon dioxide in this room that person is already feeling the effects, to protect myself I will yawn too!\n\nBy the way you also yawn if you're tired because you're breathing naturally slows which makes carbon dioxide build up more easily.  You will yawn when you are tired to expel this excess carbon dioxide!
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.