Despite the fact that virtually every human yawns on a daily basis, its function is still largely a mystery. In this Spotlight feature, we delve into the baffling world of yawn science, touching on topics as diverse as schizophrenia, empathy, chimpanzees, and sexual arousal.
Not a great deal of research has gone into studying yawning; it has not necessarily captured scientists’ imagination en masse. But, once you start to peel back the layers, there is much to talk about.
The process of yawning seems relatively simple: the mouth opens, there is a swift intake of air, a brief pause in breathing, a longer expiration, and sometimes an accompanying stretch.
But that is far from the full list of events. A yawn is a relatively complicated behavior, spread over an average of 6 seconds.
Facial muscles stretch and the head tilts back. The eyes narrow or close and can often water. Saliva is produced, and the Eustachian tubes of the middle ear are opened. Beyond this, there are probably cardiovascular, neuromuscular, and respiratory changes that we are yet to define.
It is common knowledge that we yawn when we are bored or tired, and studies have demonstrated this to be scientific fact. However, there are also reports of paratroopers yawning before a skydive, musicians yawning before hitting the stage, and dogs yawning before they attack – all of which mean that there is obviously more to the yawn than sleepiness.
The sexuality of a yawn
Interestingly, the yawn shares a number of components with other behaviors. For instance, there are some similarities between the “yawn face” and the “orgasm face.” Some researchers believe that there may be common origins, and although at first glance that may seem a little absurd, there is some evidence of a link. For a start, yawning is triggered by androgens (male sex hormones) and oxytocin. Furthermore, most drugs that produce stretching and yawning in rats also cause penile erection.
Another intriguing link between sex and yawning concerns antidepressants. Drugs including clomipramine and fluoxetine tend to depress sexual desire, and in some people, they also produce an odd side effect: their yawns trigger orgasm.
We have all been yawning since we were in the womb, and a whole host of animals – from flies to snakes, and from bears to badgers – all indulge. It is clearly an ancient behavior, and the fact that it has been conserved throughout evolution means that it must do something useful.
The program that controls yawning appears to rest in an ancient part of the brain, too. As an example, patients with amyotrophic lateral sclerosis who are “locked in” and who have virtually no control over their muscles can yawn normally. Neurologists believe that this means the yawn coordinates are kept in the brainstem, an evolutionarily old part of the brain, along with the centers responsible for controlling breathing and vascular tone.
One of the most interesting things about yawns are their contagious prowess. As you read this article, many of you will be yawning as a result of simply thinking about it.
According to Robert R. Provine, the most prolific yawn researcher, he himself has become a “yawn stimuli.” Because his friends are all aware of his work, he simply has to enter a room and people begin to yawn.
Human-to-human yawn infection is well documented. However, it is not contagious in children until they reach around 5 years of age.
Catching yawns in non-human animals is much less common, but it has been observed in chimpanzees and some other primates.
A study looking at yawning in gelada baboons found that yawns were more contagious among individuals that shared a closer relationship, as measured by levels of grooming. A similar observational study on bonobos also found that a yawn is more likely to be contagious when it is spread between individuals that are more closely bonded.
Aside from primates, it has been demonstrated that dogs more easily catch yawns from their owner than from a stranger, which provides more evidence that being close knit enhances the yawn bond.
To some researchers, these findings mean that yawning might offer an intriguing insight into the human mind – specifically, an insight into primal empathy.
Researcher Steven Platek and his colleagues conducted a study in which participants received MRI scans while watching other people yawning. Activity was measured in the posterior cingulate and precuneus brain regions. These areas are involved in self-referencing, theory of mind, and autobiographical memory. The authors conclude:
This potential measure of empathy could prove useful in relation to certain mental conditions. For instance, in disorders such as autism and schizophrenia, an individual’s ability to assess other people’s emotions and motivations are substantially reduced.
As an example, one study published in 2009 found that individuals with schizophrenia were less susceptible to both yawn and laughter contagion.
Not everyone believes that yawning is linked with empathy, however. An experiment published in PLOS One found only one significant predictor of yawn contagion: age. Older people were significantly less likely to yawn when watching a video of people yawning than younger people were. The researchers also found that an individual’s level of empathy (as assessed by questionnaires), time of day, and intelligence were not significant predictors of one’s likelihood to catch a yawn.
Either way, there certainly is a social aspect to yawns – but that fails to answer the question of why we yawn, specifically. It could just as easily be sneezing or hiccups that are contagious, so why is it this long, deep breath?
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