why is yawning contagious?
448013
"The Physiological Theory \n-- 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. \n\nThe Evolution Theory \n-- 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. \n\nThe Boredom Theory \n-- In the dictionary, yawning is said to be caused by boredom, fatigue or drowsiness. Although we do tend to yawn when bored or tired, this theory doesn't explain why Olympic athletes yawn right before they compete in their event. It's doubtful that they are bored with the world watching them. \n\nThe simple truth is that even though humans have been yawning for possibly as long as they have existed, we have no clue as to why we do it. Maybe it serves some healthful purpose. It does cause us to draw in more air and our hearts to race faster than normal, but so does exercise. There's still much we don't understand about our own brains, so maybe yawning is triggered by some area of the brain we have yet to discover. We do know that yawning is not limited to man. Cats, dogs, even fish yawn, which leads us back to the idea that yawning is some form of communication."
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.
664075
Researchers aren't really sure. They seem to have pinpointed the initiation to a particular part of the brain, and speculate that it's a synchronized social reflex that may serve an evolutionary goal of greater tribal cohesiveness and mutual protection. See the referenced web page. I've noticed that it's not just other people yawning, but even reading the word 'yawn' that does it for me, even if I'm well oxygenated and wide awake!
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.
922965
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. Studies 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\nalso when we someone else yawn if someone else yawns, we are naturally competitive so if someone else is getting more oxygen, our body wants more.
178925
The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.\n\nHerd Instinct\n-------------\nThe so-called herding instinct is a social tendency in humans to identify with and model many behaviors and beliefs after a larger group of individuals with whom they identify. This is sometimes referred to as "following the herd." Such people are sometimes labelled with the derogatory term "sheeple."\n\nSince the herding instinct includes both behavior and belief, the term 'herd behavior' describes only a part of this complex phenomenon in humans.
1049703
Good question!\nMany people believe that we yawns are the cause of to get rid of extra carbon dioxide and to take in more oxygen. Not entirely true (see ref 1 and 3). Sometimes we yawn as we shift phases from being awaken, to feeling sleepy, and anytime during our awakened state. And sometimes they simply are contagious(2).\n\n"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. "(3)
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.
461426
Seeing running water makes you want to go, it's the same with yawning, it's an involuntary reaction to seeing someone else do it before you. \nAn Auto suggestive sequence and it can spread.
355807
It is possible that yawns are contagious because at one time in evolutionary history, the yawn served to coordinate the social behavior of a group of animals. When one member of the group yawned to signal an event, all the other members of the group also yawned. Yawns may still be contagious these days because of a leftover response (a "vestigial" response) that is not used anymore. None of this has been proven true and yawns are still one of the mysteries of the mind.
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
326667
Here are some very cool links about yawning in general and why it is contagious:\n\nhttp://www.howstuffworks.com/question572.htm\n\nhttp://staff.washington.edu/~chudler/yawning.html\n\nhttp://www.world-science.net/exclusives/050309_yawnfrm.htm\n\nBy the way, excellent question.  Hope this helps.\n\nGod Bless!  :)
1051186
When a person yawns it is usually due to the lack of oxygen to the brain. When we see a person yawning our brain interprets  it as low level of oxygen in the air.As a result we yawn.
414199
Yawning, like laughter, can be infectious. As to why this should be, there is little hard evidence, although yawning may be an arousal response that arose early in evolution and whose aim is to improve oxygenation of brain tissue and increase alertness, with a view to enhanced survival. In social groupings, the sight of one member yawning might act as a signal to cause other members to yawn - in some way the yawn is a warning that attention is slipping and the group may be at risk…\n\nResearch into the physiology and pathology of yawning appears to be quite limited. However, I have come across a couple of useful references. The first gives a general description of what happens when we yawn:\n\n"Yawning is a response to a wide variety of stimuli, including sleepiness and an awakening from sleep, hunger, boredom, nervousness, and intracranial disease. It is infectious, occurs more frequently in the newborn, and is likely to be more vigorous (especially the accompanying stretch) in early morning than late at night."\n\n"A yawn consists of an expansion of the chest, descent of the diaphragm and larynx, elevation of the ala nasi and soft palate, downward and backward movement of the tongue, abduction of the vocal cords, wide opening of the mouth, contraction of the tensor veli palatini muscle, closing of the eyes, lacrimation, pulling the head backwards, stretching of the upper arms sideward and the lower arms upward, and, less frequently, stretching of the legs. Vasoconstriction in the digits and cardiac acceleration have also been found to accompany the yawn. The whole act occupies 5 to 10 seconds, most of which time is spent in the inspiratory phase."\n\n"Although yawning certainly is an effective way of fully expanding the lungs and increasing the venous return to the heart, its psychic implications are also of great interest. The author finds that merely writing this is a potent stimulus towards yawning, and perhaps the reader is similarly stimulated." (Fenn and Rahn 1964)\n\nA good review of yawning is provided by Askenasy (1989), and the points that follow are derived from this source. Apparently, yawning movements have been observed in fetuses as early as the 15th week after conception, and continue to occur sporadically throughout the remainder of pregnancy. The newborn baby yawns a few minutes after birth. The frequency of yawning gradually diminishes as the baby matures\n\n\nSeveral causes of yawning are discussed in the review:\n\n psychological - this includes boredom, drowsiness, fatigue, separation, imitation, and autosuggestion \n\n hormonal - ACTH and MSH \n\n neurological - various brain pathologies including coma, encephalitis, hypoxia, and neoplasms \n\n psychiatric - for example schizophrenia, psychosis, depression and withdrawal \n\n general pathologies - ear disorders, gastric and biliary disorders, and motion sickness \n\n drug overdose - for example naloxone, valproate, imipramine, clomipramine, seratonin, and pentobarbital \n\n drug withdrawal - from heroin, morphine, lefetamine, methadone, and pentazocin.
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!
476267
I have no idea, but it happens every time I yawn LOL. I have seen people do it intentionally though.
609665
Because they trigger the receptors in the brain to relax.  Yawning signals relaxation to other humans, thus causing themselves to inadvertantly yawn.  It's like human relation reflex.