The yawn reflex is often described as contagious: if one person yawns, this may cause another person to “sympathetically” yawn. Observing another person’s yawning face (especially his/her eyes), even reading, or thinking about yawning, can cause a person to yawn. The proximate cause for contagious yawning may lie with mirror neurons, i.e., neurons in the frontal cortex of certain vertebrates, which upon being exposed to a stimulus from conspecific (same species) and occasionally interspecific organisms, activates the same regions in the brain. Mirror neurons have been proposed as a driving force for imitation which lies at the root of much human learning, e.g., language acquisition. Yawning may be an offshoot of the same imitative impulse. A 2007 study found that children with autism spectrum disorder do not increase their yawning frequency after seeing videos of other people yawning, in contrast to typically developing children. This supports the claim that contagious yawning is based on the capacity for empathy.
To look at the issue in terms of evolutionary advantage, if there is one at all, yawning might be a herd instinct. Other theories suggest that the yawn serves to synchronize mood in gregarious animals, similar to the howling of the wolf pack. It signals tiredness to other members of the group in order to synchronize sleeping patterns and periods. This phenomenon has been observed among various primates. The threat gesture is a way of maintaining order in the primates’ social structure. Specific studies were conducted on chimpanzees and stump tail macaques. A group of these animals was shown a video of other con specifics yawning; both species yawned as well. This helps to partly confirm a yawn’s “contagiousness.”
Gordon Gallup, who hypothesizes that yawning may be a means of keeping the brain cool, also hypothesizes that “contagious” yawning may be a survival instinct inherited from our evolutionary past. “During human evolutionary history when we were subject to predation and attacks by other groups, if everybody yawns in response to seeing someone yawn, the whole group becomes much more vigilant, and much better at being able to detect danger.”
A recent study by the University of London has suggested that the “contagiousness” of yawns by a human will pass to dogs. The study observed that 21 of 29 dogs yawned when a stranger yawned in front of them, but did not yawn when the stranger only opened his mouth.
Interesting yawning facts
- 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
- Olympic athletes often yawn before competition
In non-human animals, yawning can serve as a warning signal. For example, Charles Darwin, in his book The Expression of the Emotions in Man and Animals, mentioned that baboons use yawn to threaten their enemies, possibly by displaying large, canine teeth. Similarly, Siamese Fighting Fish yawn only when they see a con specific (same species) or their own mirror-image, and their yawn often accompanies aggressive attack. Guinea Pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth, this is often accompanied by teeth chattering, purring and scent marking. Adelie 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. This trait has also been seen among Emperor Penguins. Researchers have been attempting to discover why these two different species share this trait, despite not sharing a habitat. Snakes yawn, both to realign their jaws after a meal, or for respiratory reasons, as their trachea can be seen to expand when they do this. Dogs often yawn after seeing people yawn.
Certain superstitions surround the act of yawning. The most common of these is the belief that it is necessary to cover one’s mouth when one is yawning in order to prevent one’s soul from escaping the body. The Ancient Greeks believed that yawning was not a sign of boredom, but that a person’s soul was trying to escape from its body, so that it may rest with the gods in the skies. This belief was also shared by the Maya.
Several superstitions have been concocted regarding the act of yawning and the harm that the act can do to the individual yawning. These superstitions may not only have arisen to prevent people from committing the faux pas of yawning loudly in another presence—one of Mason Cooley’s aphorisms is “A yawn is more disconcerting than a contradiction” — but may also have arisen from concerns over public health. Polydore Vergil, in his De Rerum Inventoribus, writes that it was customary to make the sign of the cross over one’s mouth, since “alike deadly plague was sometime in yawning, wherefore men used to fence themselves with the sign of the cross…which custom we retain at this day.”
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