Why Animals Yawn?
Why Animals Yawn?
In 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 yawn to threaten their enemies, possibly by displaying large canine teeth. Similarly, Siamese fighting fish yawn only when they see a conspecific (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," opening their beaks and pointing their faces 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 and for respiratory reasons, as their trachea can be seen to expand when they do this. Dogs often yawn after seeing people yawn and when they feel uncertain. Fish can also yawn, and they increase this behavior due to lack of oxygen or excessive heat.
The Oxford English Dictionarv describes yawning in the context of boredom, whereas Gray’s Anatomy and the Encyclopedia of Human Biology do not even show yawning in their indexes. To the extent that they consider it at all, most lay people and physicians appear to believe that yawning is a respiratory phenomenon, a way to get oxygen to the brain. In fact, there is meager evidence for this respiratory hypothesis and, on the basis of this review, it appears to be an incomplete explanation at best.
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