The yawn reflex has long been observed to be contagious: in 1508, Erasmus wrote: "One man's yawning makes another yawn," and the French proverbialized the idea to "Un bon bâilleur en fait bâillier deux." ("One good gaper makes two others gape"). Often, 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, or looking at a yawning picture can cause a person to yawn. Chances are you have already yawned at least once while reading this article! 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 young children with autism spectrum disorders do not increase their yawning frequency after seeing videos of other people yawning, in contrast to typically developing children. In fact, the autistic children actually yawned less during the videos of yawning than during the control videos. This supports the claim that contagious yawning is related to empathic capacity.
This phenomenon has been observed among various primates. Here the yawn is a threat gesture, 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 conspecifics yawning; both species yawned as well. This helps to partly confirm a yawn's "contagiousness."
The Discovery Channel's show Mythbusters also tested this concept. In their small scale, informal study they concluded that yawning is contagious.
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.
