Yawn

A yawn is a reflex consisting of the simultaneous inhalation of air and the stretching of the eardrums, followed by an exhalation of breath.Charles Darwin, Notebook M (1838), 65Barred owlCrabeater seal (Lobodon carcinophaga)Juvenile Japanese macaquePonyCatMale lionBengal tigerJaguarHippopotamus (Hippopotamus amphibius) A yawn is a reflex consisting of the simultaneous inhalation of air and the stretching of the eardrums, followed by an exhalation of breath. Yawning (oscitation) most often occurs in adults immediately before and after sleep, during tedious activities and as a result of its contagious quality. It is commonly associated with tiredness, stress, sleepiness, or even boredom and hunger. In humans, yawning is often triggered by others yawning (e.g. seeing a person yawning, talking to someone on the phone who is yawning) and is a typical example of positive feedback. This 'contagious' yawning has also been observed in chimpanzees, dogs, cats, birds, and reptiles and can occur across species. Approximately 20 psychological reasons for yawning have been proposed by scholars, but there is little agreement on the primacy of any one. During a yawn, the tensor tympani muscle in the middle ear contracts, creating a rumbling noise from within the head. Yawning is sometimes accompanied, in humans and other animals, by an instinctive act of stretching several parts of the body, including arms, neck, shoulders and back. English yawn continues a number of Middle English forms, yanen from Old English ġānian, and yenen, yonen from Old English frequentatives ġinian, ġionian, from a Germanic root *gīn-. The Germanic root has Indo-European cognates, from a root *g̑hēi-found also with -n- suffix in Greek χαίνω 'to yawn', and without the -n- in English gap (compare the figura etymologica in Norse ginnunga-gap), gum 'palate' and gasp (via Old Norse), Latin hiō, hiatus, and Greek chasm, chaos. The Latin term used in medicine is oscitatio (anglicized as oscitation), from the verb oscito 'to open the mouth'. Pandiculation is the act of yawning and stretching simultaneously. There are a number of theories that attempt to explain why humans and other animals yawn. It is likely that there are a number of triggers for the behavior. However, there are comparatively few theories that attempt to explain the primary evolutionary reason for the yawn. One study states that yawning occurs when one's blood contains increased amounts of carbon dioxide and therefore becomes in need of the influx of oxygen (or expulsion of carbon dioxide) that a yawn can provide. Yawning may, in fact, reduce oxygen intake compared to normal respiration. However, neither providing more oxygen nor reducing carbon dioxide in air decreased yawning. Another proposal points out that animals subject to predation or other dangers must be ready to physically exert themselves at any given moment. At least one study suggests that yawning, especially psychological 'contagious' yawning, may have developed as a way of keeping a group of animals alert. If an animal is drowsy or bored, it may not be as alert as it should be - to spring into action. Therefore, the 'contagious' yawn could be an instinctual reaction to a signal from one member of the group reminding the others to stay alert. Nervousness has also been suggested as a possible reason. Nervousness often indicates the perception of an impending need for action. Anecdotal evidence suggests that yawning helps increase the state of alertness of a person. Paratroopers have been noted to yawn in the moments before they exit the aircraft.