Yawning. One of life’s greatest mysteries, right up there with the origin of the universe and what the cream filling in an Oreo is made of (hint: it’s not cream).
Sure, we have a general idea of why we yawn. Maybe there are already too many ideas about yawning--the Wikipedia page "Yawn" says there are 20 proposed functions of yawns (including, hilariously, “brain cooling”). People seem to yawn when they are bored or sleepy. It’s obvious that yawning forces a large intake of air, so hypotheses about why we yawn tend to focus on increased oxygen intake, perhaps as a way to perk you up when you’re tired. After all, yawning feels good. When the urge takes over, fighting a yawn is excruciating and giving in to it is pure double-chinned pleasure. But if yawning is purely about maintaining bodily homeostasis by giving your brain an oxygen hit, why is it so contagious?
Have you yawned yet from just thinking about yawning? If you haven’t, don’t worry. You will.
Yawns: The “Everybody be Cool” Signal of the Dog World
I am tackling the issue of yawning because I think dog behaviorists have had an insight that is useful for human psychology. Yawning is classified by dog trainers as a calming signal, or a stereotypical behavior dogs will do when they are somewhat stressed or want to de-escalate a potentially threatening interaction. Other calming signals include lick lipping, paw lifting, lying belly-down on the floor, and turning the head away.
I don’t think every yawn a dog produces could be construed as a social calming signal—sometimes dogs yawn in contexts we humans would easily recognize, such as when they are waking up from a nap. However, if your dog yawns when you’re in a crowded, overwhelming place, when you lean over to pick her up, or when she’s at the vet, you should interpret the yawn as a calming signal.
When dogs yawn in a social context, behaviorists think of it as accomplishing several things:
- It relaxes the slightly aroused dog.
- It signals to other dogs that the yawning dog is slightly stressed but does not pose a threat to them, and just wants everyone else to relax.
- It causes the other dogs to yawn automatically, which is why we say yawning is contagious.
All 3 of these functions serve to de-escalate the social situation and maintain group harmony.
What causes some behaviors to serve as calming signals, as opposed to others? Different trainers classify different behaviors as calming signals (some claim there are as many as 30), but all of the behaviors seem to be either naturally rewarding and relaxing, or they functionally de-escalate a potentially intense social situation. Lick lipping is a self-soothing gesture that feels good, like the dog equivalent of hugging yourself or touching your face when you’re anxious. Turning their heads away from someone who stresses them out is like covering your eyes during a scary movie; thus, head turns are a calming signal. Lying down on the ground is probably calming because it shows others that the dog isn't about to fight and it is difficult for the dog to feel tense and reactive when she is prostrate—in fact, being in a supine posture changes how people experience anger, presumably because they can't get into an "angry" posture (1).
So, then, why is yawning included the calming signal repertoire?
It feels intrinsically good and rewarding.
Why Yawning Feels Good
Inhaling deeply is a well-known relaxation strategy. People who practice mindfulness meditation use it (2), people on juice cleanse/yoga retreats use it, Harvard doctors use it, even THE Doctor uses it.
A recent experiment demonstrated the relaxing effects of sighing. Research subjects were instructed to either hold their breath or breathe deeply while they waited for positive or negative images to appear on a screen. The images in these studies can be intense, so I imagine that knowing you're about to see a negative image of some kind is fairly stressful. Subjects who were breathing deeply reported feeling greater relief and reduced muscle tension when they were anticipating negative images, compared to subjects holding their breath. Even when subjects spontaneously sighed during the task their muscle tension decreased (see also 3, 4, 5 for more information on the mental and physical health benefits of deep breathing).
One physiological function of sighing is to reinflate your lungs’ alveoli, which are tiny air sacs that collapse when they aren’t used (6). If we didn’t sigh every few minutes, our lungs wouldn’t function properly. Deep breaths are fundamental to survival, so much so that artificial sighs are induced every so often in people on ventilators.
I don’t see why yawning would be categorically different from sighing in its function or effects. Anecdotally, sometimes I can feel a sigh morphing into a yawn, and before I know it, I’m showing my uvula to the world. Just as people and dogs yawn more when they are stressed or aroused, they also tend to sigh more when they are stressed (6). So, from now on, let's oversimplify things and consider yawning to be a less frequent and more intense version of a sigh.
We’ve already seen that sighing feels good and gives people bodily and mental relief. There are correlational reasons to believe that deep breaths like sighing and yawning are rewarding: increased presence of opioid neurotransmitters—the “reward” chemicals—in the brain reduces yawning frequency (7). On the flip side, people going through opioid withdrawal yawn more (8). If the amount of reward-related neurotransmitters in the brain is negatively correlated with the likelihood that you’ll yawn, maybe yawning is a behavior that gives the brain a quick reward. Brains that have a reward-chemical deficit trigger more frequent yawns, while brains rich in these opioids don’t need to yawn as much.
Is Yawning a Calming Signal in Humans?
Why, if sighing can achieve all the benefits of deep breathing, would you do something as dumb-looking as yawn? Maybe yawning is even more restorative to the lungs and even more rewarding to the brain, since it involves an even greater intake of air. Also, yawns are highly expressive and noticeable to others, with the double-chinned gaping mouth and the sometimes-vocalized “ahhh” noise (Lola prefers to make a little screaming noise when she yawns).
This communication signal aspect of yawning brings us back to the social contagion piece. Say you’re feeling a little stressed, so your brain signals that it’s time to get a deep breath to release some tension, and maybe get a little reward burst in the brain (we’re talking a low-level reflex here, 6). It’s worth noting that this “stress” might actually be what you’d call boredom or fatigue; both are states where you are fighting your basic motivations to go to sleep or leave the lecture hall, which is certainly going to increase stress.
To relieve some stress, you yawn, and this provides clear information to those around you that you’re not into what’s currently happening. Those around you see your yawn and may change their behavior—your friends finally stop talking about fantasy football or, if you’re a dog, that other scary dog will stop smelling your rear end. Alternatively, the people/dogs around you will also yawn to let you know that they see and understand your heightened state of uncertainty and stress. It’s well-documented that unconsciously mimicking the behavior of others signals affiliation (9) and people mimic the yawns of friends more than strangers (10; for more on the possible social origins of yawning, see 11).
The contagiousness of yawns, then, aligns group members’ emotional states, signals group cohesion, and gets everyone in the group to relax a bit.
Amazingly, all of this happens without anyone being consciously aware of the social functions of yawning.
A hypothetical and untestable evolutionary story (my favorite kind of story to tell) goes as follows. Animals developed reflexive deep-breath behaviors like sighing and yawning to maintain good lung alveoli health. These deep breaths relieve physical and mental stress by restoring respiratory health and, speculatively, releasing rewarding neurotransmitters in the brain. Animals therefore sigh or yawn more often when they are stressed or deprived of other reward resources. As certain mammals like dogs and humans evolved to be highly social, they started to produce yawns not just to restore their own homeostasis, but also that of the group. Because these social animals are highly attuned to the bodily expressions of members of their social group, they understand and “catch” each others’ yawns, which keeps the group synchronized and at peace.
Go on, yawn
Don’t hold back. Yawning will release tension and feel good, plus it is healthy for your lungs. Although culturally it is sometimes considered rude to yawn, especially when others are speaking, it’s your body’s honest way of expressing and relieving stress. If your yawn causes a ripple effect of yawns among those around you, yay! You’re well-liked and have lots of people who are highly attuned to your mental state.
If your dog yawns, yawn back (throw in an exaggerated yawn-squeak for good measure). It’ll show him that you acknowledge his stress and make him feel more comfortable. Try yawning at your dog when you don’t like his behavior—if he’s being pushy or rude—or when you just want to help him relax. Human yawns are contagious to dogs (12) and can influence their behavior.
Us mammals are so cool.
- Harmon-Jones, E., & Peterson, C. K. (2009). Supine body position reduces neural response to anger evocation. Psychological Science, 20(10), 1209-1210.
- Wielgosz, J., Schuyler, B. S., Lutz, A., & Davidson, R. J. (2016). Long-term mindfulness training is associated with reliable differences in resting respiration rate. Scientific reports, 6, 27533.
- Brown, R.P., Gerbarg, P.L., & Muench, F. (2013). Breathing practices for treatment of psychiatric and stress-related medical conditions. Psychiatric Clinics of North America, 36, 121-140.
- Jerath, R., Crawford, M. W., Barnes, V. A., & Harden, K. (2015). Self-regulation of breathing as a primary treatment for anxiety. Applied psychophysiology and biofeedback, 40(2), 107-115.
- Sakakibara, M., & Hayano, J. (1996). Effect of slowed respiration on cardiac parasympathetic response to threat. Psychosomatic Medicine, 58(1), 32-37.
- Li, P., Janczewski, W. A., Yackle, K., Kam, K., Pagliardini, S., Krasnow, M. A., & Feldman, J. L. (2016). The peptidergic control circuit for sighing. Nature.
- Argiolas, A., & Melis, M. R. (1998). The neuropharmacology of yawning. European journal of pharmacology, 343(1), 1-16.
- Handelsman L., Cochrane K.J., Aronson M.J., Ness R, Rubinstein K.J., & Kanof P.D. (1987). Two new rating scales for opiate withdrawal. American Journal of Drug and Alcohol Abuse, 13, 293-308.
- Lakin, J. L., Jefferis, V. E., Cheng, C. M., & Chartrand, T. L. (2003). The chameleon effect as social glue: Evidence for the evolutionary significance of nonconscious mimicry. Journal of nonverbal behavior, 27(3), 145-162.
- Norscia, I., & Palagi, E. (2011). Yawn contagion and empathy in Homo sapiens. PloS one, 6(12), e28472.
- Guggisberg, A. G., Mathis, J., Schnider, A., & Hess, C. W. (2010). Why do we yawn?. Neuroscience & Biobehavioral Reviews, 34(8), 1267-1276.
- Joly-Mascheroni, R. M., Senju, A., & Shepherd, A. J. (2008). Dogs catch human yawns. Biology Letters, 4(5), 446-448.