Everybody yawns- both people and animals. Even fish and snakes! But only humans and chimpanzees, and possibly dogs, yawn when they see someone else yawn- aka the “contagious yawn”. It definitely appears to be contagious; when one person in a room yawns, about half of the people in the room will then yawn.
What is a yawn? The most common definition is that it is an involuntary action that causes us to open our mouths wide and breathe in and out deeply. That, in turn, causes the inhalation of oxygen and the stretching of the ear drum, followed by exhalation of carbon dioxide. That is the physical process, but what facts do we actually know about yawning based on research? We have learned that 40 to 60 per cent of adults yawn when they see someone else yawn. The average yawn is 6 seconds long. We also know that humans don’t engage in contagious yawning until about 4 years of age despite the fact that they have documented fetuses as young as 11 weeks of age yawning. Research has also shown us what yawning is not; several studies have debunked the myth that yawning is due to a lack of oxygen or too much carbon dioxide.
Why do we Yawn?
There is no generally accepted theory to explain the cause of yawning or contagious yawning. There are, however, a variety of theories that reflect either a physiological basis or a social-emotional basis. Several theories have been formulated in the past which looked at mostly physiological causes. As previously mentioned, one of the first theories hypothesized that when a person was bored or tired they breathed more shallowly so their body took in less oxygen. They theorized that yawning helps bring more oxygen into the bloodstream and moved carbon dioxide out of the blood. Thus they claimed that yawning is an involuntary reflex that helped control oxygen and carbon dioxide levels in the body. From there, they reasoned that people yawn in groups because groups take more oxygen out of the air and produce more carbon dioxide. That seemed to make sense; however, studies have shown that breathing in more oxygen does not decrease yawning and increasing carbon dioxide did not increase yawning.
Another theory states that yawning stretches the lungs and lung tissue. When you yawn and stretch, it is a way to flex your muscles and joints, increase heart rate and feel more alert and awake. The purpose of yawning is to make the body more alert. It is true that yawning can increase heart rate by up to 30%. This theory has not been disproved; but it appears to be more of a statement as to what yawning does rather than the cause of yawning.
Yet another theory, which is still a widely held belief today, is that yawning is caused by boredom. Although you might want to blame your spouse or a long-winded professor for causing you to yawn, that would not explain why so many professional athletes yawn just before they compete. Nor does it explain why a dog yawns just before it attacks. Or why a fish yawns when the water temperature is too high or lacks sufficient oxygen.
More recently, the theory that yawning promotes brain-cooling has been touted in the news. It is a popular idea and supported by studies that demonstrated that people who engaged in brain-cooling techniques (such as breathing through their nose or pressing a cold pack to their forehead) nearly eliminated contagious yawning and appeared to be more alert and able to think more clearly. They found that the subjects yawned more when they were in situations where their brain was likely to be warmer (pressing a warm pack to their forehead, etc). The conclusion was that yawning developed as a means to keeping us alert (Andrew Gallup, 2007).
Is Yawning Contagious?
As for contagiousness, another recent theory holds that the cause for contagious yawning may be due to ‘mirror neurons’ in the frontal cortex. Mirror neurons have been implicated as a primary force for imitation- which lies at the root of much human learning such as verbal and nonverbal language acquisition. This was supported by a 2007 study that found that children with autism, as compared to a control group, did not increase their yawning after seeing videos of other people yawning. In fact, they actually yawned less than during the control video!
Other theorists place more focus on the social-emotional reasons for yawning rather than physiological causes. Most of them agree that yawning when others yawn is related to empathy and some say it is also a form of social bonding. They propose that contagious yawning shows an emotional link to those around us. Empathy is the ability to recognize and share the emotions that others feel; emotional contagion is when the emotion of others influences your feelings. For example, being around happy people tends to make you feel happier. Contagious yawning, although not an emotion, would seem to reflect both of those concepts. A 2011 behavioral study at the University of Pisa revealed that only social bonding was able to predict the occurrence, frequency, and latency of yawn contagion. The rate of contagion was found to be greatest in response to relatives, followed by friends, then acquaintances and lastly strangers. The closer you are emotionally to someone, the more likely contagious yawning is likely to take place. Yawning is contagious, as is contagious laughing (or contagious crying) – it’s a shared experience that promotes social bonding.
Senju, A; Maeda, M; Kikuchi, Y; Hasegawa, T.; Tojo, Y.; Osani, H. (2007) “Absence of contagious yawning in children with autism spectrum disorder” BIOLOGY LETTERS 3(6):706-8
Norscia, Ivan; Palagi, Elizabeth (2011). Rogers, Lesley, Joy, ed. “Yawn Contagion and Empathy in Homo sapiens” PLoS ONE 6(12): e28492
Gallup, Andrew (2007). “Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning”. EVOLUTIONARY PSYCHOLOGY 5(1): 92-101