A “yawn” as defined by Dictionary.com is said to be “to open the mouth somewhat involuntarily with a prolonged, deep inhalation and sighing or heavy exhalation, as from drowsiness or boredom.” The word yawn is derived from the Old English word meaning to gape or open wide. The average human yawns 240,000 times in a lifetime and the average yawn lasts about six seconds.
Many believe that a yawn is in response to excess carbon dioxide or shortage of oxygen in the lungs. This notion is false and probably assumed because of the gasp that takes place at the end of yawns.
While yawns are typically seen as a comical occurrence, it is now known that excessive yawning can signify a brain tumor, narcolepsy, hemorrhages, opiate withdrawal, chorea, encephalitis and other internal issues.
Stretching is usually accompanied by a yawn; however, they are not dependent on each other. Also, the face that is formed when yawning stretches the face and is possibly one of the reasons that yawns are so satisfying. On a scale from one to 10 (10 being most satisfying), the average rating was 8.5.
All vertebrate animals yawn in the same fashion as humans. Also, yawning is not exclusive to mammals. Crocodiles, sharks, snakes and birds all yawn. The purpose of their yawning is unknown as well.
Reading about yawning stimulates yawns, similarly to seeing someone yawn makes you have to desire to yawn. (I’ve yawned about 30 times while writing this). The yawn alone is not what is contagious. In fact, the entire facial stretch that accompanies the yawn causes others to feel the need to replicate the face. Therefore, even when you cover your mouth, the “yawn face” is still present in the eyes and can cause others to yawn. Contagious yawning is thought to be an ancient way of communicating bedtime.
Recent studies have shown that yawning may not be linked to sleepiness or boredom whatsoever, and may be needed in order to cool the brain. This theory is generated from medical observations such as epileptics yawning excessively before a seizure. Now yawning can be used as a signal to greater problems, especially with diseases or disorders that affect the brain’s temperature. Additionally, some animals that do not sweat such as dogs and pigs may use yawning to cool their bodies, even if just by a fraction of a degree.
While most aspects of yawning are still a mystery, it is clear that if you are yawning very often you are likely not getting enough sleep or extremely bored. Though many theories are continuously being developed, no proven function has been identified.