Yawn! Yawn! Yawn! Yawn! Yawn! Contagious Yawn!

It's been a pretty long stressful week around here, and not just because of Pepsipocalypse and the resulting fallout. But, well, I'm back, and I have an awesome paper to tell you about. When I saw it I just KNEW it had to be blogged.

Mythbuster Adam Savage sets the yawning in motion in Mythbusters attempts to start a yawning epidemic across the globe

ResearchBlogging.orgDid watching that video make you yawn? Chances are it did, and you can thank contagious yawning for it. What is contagious yawning? Contagious yawning is a very well-dcoumented phonemenon wherein yawning is triggered by the perception of others yawning. Originally, scientists thought that contagious yawning was the result of a releasing mechanism - in other words, seeing someone yawn flipped the yawning-switch in the brain, and it makes you yawn. But it actually turns out that there is a correlation between the susceptibility for contagious yawning and self-reported empathy. Converging evidence for the empathy hypothesis comes from the fact that contagious yawning is absent in individuals with autism spectrum disorder.

Spontaneous yawning is known to occur through a ton of vertebrate species, but until recently, contagious yawning only seen in humans, chimpanzees, and potentially in stumptail macaques (though this is still unclear). But domesticated dogs, since they are so good at reading human social and communicative cues, might show contagious yawning as well, and that is exactly what this study was designed to investigate.

As we've discussed before, dogs' unique social skills in interacting with humans is probably the result of selection pressures during the domestication process. So it's possible that as a result of that process, they may have developed the capacity of empathy towards humans. And if so, it is further possible that they may yawn when perceiving humans yawn.

Twenty-nine adult dogs (12 females, 17 males) were tested at home during the middle of the day, in two conditions. In one condition, the experimenter, who was a stranger to the dogs, attracted the dog's attention and then initiated a yawn comprising both physical movement and vocalization. The yawn was repeated for five minutes after re-establishing eye contact with the dog, which meant that the number of yawns varied between ten and nineteen per individual. The control condition was identical, except that the experimenter displayed a fake yawn, which mimicked the mouth opening and closing actions, but not the vocalization or other subtle muscular changes.

contagious yawn.jpg

Figure 1: Examples of the two conditions. Yawn on the top, control below.

The yawning condition made the dogs yawn for 21 out of 29 individuals, and none of the dogs yawned in the control condition. Further, no yawns were observed in the interval between the two conditions (there was a five minute break between each of the five-minute-long conditions). During the yawning condition, dogs yawned an average of 1.9 times, and there were no sex or age differences, and there was no effect of the order in which the conditions were presented.

That's pretty amazing when you stop to think about it! Human yawns are possibly contagious to dogs! Seventy-two percent of the dogs tested yawning in response to human yawns. Amazingly, this is even higher than rates reported for humans (which range from 45-60%) and in chimpanzees (33%). Since no dogs yawned during the control condition, the results can't be attributed to the presence of the stranger, or human mouth movements in general, or anything like that. This is also the first recorded example of contagious yawning between two species!

dog yawn.jpg

Figure 2: A dog catching a human yawn. In (a) the dog observes the human yawning, in (b) the dog starts yawning as the human finishes (reflected in the mirror behind the dog), and in (c) the dog completes the yawn. (Click to enlarge)

So what might explain why human yawns make dogs yawn? In accordance with the current theory for human contagious yawning, it could reflect dogs' empathy towards humans. Dogs are really good at reading human social signals (e.g. finger pointing, eye gaze, etc), and it is possible that they can represent humans' actions in their minds and consequently adjust their own behavioral and autonomic responses.

Another possibility is that the dogs' yawns could be the result of mild tension or stress (this is the alternative explanation for contagious yawning in stumptail macaques, as well). Unfortunately, physiological data (such as cortisol levels or heart rate) were not available in this study, so this can't be entirely ruled out. However, the fact that the dogs did not yawn during the control condition suggests that the results are probably not attributable to stress more generally, such as the presence of the unfamiliar experimenter.

So I think this is a pretty cool study, aside from the fact that I've been yawning for the entire time I've been writing this. But the book is not yet closed on this question. For one thing, someone should do a study that collects both behavioral responses as well as physiological data to account for acute stress responses. Also, someone should do a study looking at contagious yawning between dogs, as opposed to between dogs and humans. If they acquired contagious yawning due to domestication, then it is possible that dogs are actually more sensitive to human yawns than dog yawns. So if I was going to do a follow-up study, one thing I'd do is look at infant puppies, to see if contagious yawning is innate (it appears to be innate in humans), or if it requires experience. I would also compare infant and adult dogs to infant and adult domesticated foxes, as well as undomesticated wolves (perhaps both wild, as well as hand-reared). I might also look at other domesticated animals, such as horses (do horses even yawn?)

I wonder if I'm really tired now because I've been yawning so much, or simply because it's pretty late?

baby yawn.jpg

Joly-Mascheroni, R., Senju, A., & Shepherd, A. (2008). Dogs catch human yawns Biology Letters, 4 (5), 446-448. DOI: 10.1098/rsbl.2008.0333


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^ NB the above yawn does not denote boredom.

I always thought yawning was contagious across many vertebrate species so I'm rather surprised there's so little evidence for this in the literature. This definitely needs more research.

This post reminds me of a BBC documentary I saw about 10 or 15 years ago, narrated by David Attenborough, about sleeping and the painful process of waking in various animal species. I can't find anything about this online but it showed that humans are by no means the only ones that have severe trouble with the waking-up process.
If one of your readers has more information on this it would be great to hear about it as I'd love to see that documentary again. As an added bonus it featured loads of yawning.

Interesting, but not surprising. As a side note, horses do yawn occasionally. I don't think they do it for quite the same set of reasons as humans do though. For example, if I remember correctly, they sometimes yawn to try to relieve pressure in their bellies when they have colic (stomache ache).

By Coriandre (not verified) on 14 Jul 2010 #permalink

Horses definitely yawn. I spent a huge chunk of my life training them, and I've seen it happen a whole lot. And though I know anecdotes are worth not much, it's very much contagious with them in my experience -- after a long day of training, I'd yawn, the horse I was grooming would follow suit, and whichever one was in the closest stall would catch it. Sometimes, it'd even go down the line of stalls for a minute.

They were rescues, a lot of the time, so I'm not sure they had much empathy for people, though they definitely were around human social cues. It'd be interesting to try around a bunch of, say, recently captured mustangs, to see if it's the connection to humans or something else.

They _do_ tend to try to stretch everything they possibly can with colic, but I haven't seen them yawn from it (not that it might not happen, just haven't noticed it if so, as I've usually been looking at their stance otherwise).

I left a comment a while back. It vanished. I'm going to try again, taking out the one link (which was to the abstract of one of the papers I cite). Here goes:

The researchers who generated a lot of publicity with a finding that autistics do not yawn contagiously (Senju et al., 2007) later found that autistics and nonautistics don't differ with respect to contagious yawning (Senju et al., 2009). This second finding received no publicity at all.

The only difference in task design between the 2nd study and the 1st (the only 2 studies available that I know of--if there's more, I hope someone corrects me) was the addition of a fixation cross. The 2nd study had slightly larger samples.

In neither study (Senju et al., 2007, 2009) was there any measure of empathy. It was simply assumed that autistics must be impaired in empathy.

Oddly, in the 2nd study, where nonautistic children performed at the same level as autistic children, it was not assumed that nonautistic children must lack empathy.

I believe actually (I saw the episode when it first came out, like 3 years ago) that Mythbusters said that yawning was NOT contagious. Would be interesting to look at the episode.

The whole contagious yawning (CY) equals empathy (E) story is a bit suspect: Even if CY is correlated with E, it does not follow that the latter is causing it (and see also above for some critique for the view that CY and E are correlated at all in humans). Also, why should there always be the same releasing mechanism across species? In other words: why the need to always catch yawns via an empathy route? What about the possibility that dogs may catch yawns by other mechanisms?

By anonymous (not verified) on 17 Jul 2010 #permalink

I believe actually (I saw the episode when it first came out, like 3 years ago) that Mythbusters said that yawning was NOT contagious. Would be interesting to look at the episode.

can you tell me which episode featured this?

To be honest, I'm not sure about the Mythbusters episode, but there is at least some evidence in the literature that there is contagious yawning in humans (and at least one paper showing it in dogs, and some scattered evidence for other non-human primates).

As for the empathy hypothesis, I'd say this is still an empirical question.

Oh sweet, I just made my dog yawn. :) And yes, I thought that Mythbusters said that it wasn't contagious, also.

Empathy,stress,cooling. Try to reconcile this: Fish yawn.

I ran across this article late. I am a photographer and often go to the zoo. I am a big fan of animals yawning. To get my pictures, I will stand and wait for the animals to watch me. And then I yawn. A lot. It's either them contagiously following me or I am really, really boring. Here's some of my work: