A yawn is a simple behavior, a reflex, with specific physiological functions. A yawn is a reflex consisting of a simultaneous inhalation of air and stretching of the eardrums, followed by an exhalation of breath. There are instances when yawning is followed by stretching of arms, neck, shoulders, and back. Humans are not the only ones yawning. Many species yawn, including chimpanzees, bonobos, macaques, wolves, and dogs. The study of yawning is called chasmology.
Although a simple behavior, yawning also performs social functions. It is contagious, not only within a group of individuals of the same species but also across species, as is the case with humans and dogs.
The yawn’s original function is unclear, with several explanations equally probable. According to one study, yawning causes the blood’s carbon dioxide levels to rise, which causes the blood to receive an infusion of oxygen. Another argument emphasizes the importance of stretching the neck and tongue muscles. According to a third hypothesis, yawning aids in maintaining alertness, which is essential for any predator to succeed.
Since social predators depend on one another to survive, yawning has become contagious due to its advantages (via natural selection). Another suggestion is that yawning aids in regulating the brain’s temperature. Studies have shown a link between yawning and neurotransmitters influencing different emotional states, including serotonin and dopamine. That could explain the pacifying function of yawning.
The simplest explanation for yawning being contagious is that the mirror neurons in the frontal cortex of various vertebrates, including humans and dogs, activate the corresponding area in the brain of others. Studies have shown that this mirroring effect occurs not only within the same species but also across species. Mirror neurons may explain imitation and allelomimetic behavior.
Wolf yawning is a behavior shared by wolves and dogs and is also common in other species (photo by Monty Sloan, Wolf Park, Indiana, USA).
Concerning a possible evolutionary advantage, yawning might be a herd instinct. Some say yawning in social animals synchronizes moods, much like howling in a wolf pack. It could help to synchronize sleeping and waking patterns and periods.
A study of gelada baboons revealed that yawning was contagious, particularly among socially close individuals. That makes it seem like emotional proximity, not physical proximity, is what makes individuals yawn at the same time.
Except in primates, there is little proof of contagious yawning associated with empathy. Researchers studied it in Canidae, e.g., the domestic dog and wolf. Domestic dogs have shown the ability to yawn contagiously in response to human yawns. However, since domestic dogs are skilled at reading human behavior, it is difficult to ascertain whether yawn contagion results from their evolutionary history or is solely a result of domestication. In 2014, a study observed wolves in an attempt to answer this question. The study showed that wolves are capable of yawning contagion. The study also found that how often wolves yawned in a way that made other wolves yawn depended on how close they were to each other socially. That confirmed earlier research that linked contagious yawning to emotional proximity.
In some species, yawning can serve as a warning signal. In “The Expression of the Emotions in Man and Animals,” Charles Darwin writes that baboons yawn to threaten their enemies, possibly by displaying their large canine teeth.
Studies conducted at Tokyo, Porto, and London’s Birkbeck College universities found that dogs yawn more readily when their owners yawn than when strangers do the same. They discarded the possibility of the dogs’ yawning being a stress response by monitoring their heart rates during the experiments.
The dog’s yawn is like ours and often precedes the same characteristic sound. We associate yawning with tiredness or boredom. In reality, it can express embarrassment, insecurity, excitement, and relief. Some humans yawn when they are in love, which can be embarrassing if it is mistaken for boredom!
Dogs may yawn when tired, but the yawning functions usually as a pacifying behavior (for themselves and the opponent). As we see in many other cases, a behavior originates with a particular function and gains other beneficial functions later. Yawning became a signal of friendship, of peaceful intentions. For example, a male dog may yawn if the female snarls at him during the mating ceremony. A self-confident dog yawns, showing friendliness to an insecure opponent and vice versa. Dogs yawn at us with the same functions and results. They may also yawn as a displacement activity. An owner scolding his dog is a typical situation where we can see a dog yawn. In critical training cases prone to error, as in the so-called ‘stay,’ the owner’s behavior causes the dog insecurity. A yawn is likely to follow, together with licking and muzzle-nudging. The dog ceases to display those pacifying behaviors when the owner changes behavior, say, by using a friendlier tone or more relaxed body posture.
References
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Featured image by Anton Antonsen.
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