This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
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Did it make you yawn? Well if it did then you’re not alone. Humans exhibit ‘contagious yawning’, where just seeing another individual makes you want to yawn yourself.
Why we yawn at all isn’t entirely clear. Some say it helps keep us awake, others say it has a role in group communication - a way of telling others without language when you’re ready to sleep. Another more recent suggestion is that perhaps it’s related to empathising with individuals around you.
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Individuals that are more empathetic are more likely to yawn when seeing another individual yawning. You’re also more likely to yawn if you see someone familiar to you yawn (like friends or family) yawn, than someone you don’t know.
Supporting this idea that yawning is related to empathy is the fact that it emerges in children at the same time as they develop empathy. This happens at around 5-6 years old – which is why it’s so hard to reason with children younger than this; in response to ‘how do you think Katie feels about you stealing her toy?’, little Jimmy is actually incapable of doing just this. In addition to this, autistic children, who have trouble empathising, also don’t yawn when they see others yawning unless they are instructed to fixate on the eyes of that person.
In addition to humans, other animals also seem to show contagious yawning. Supporting the idea that yawning has to do with empathy or social bonding, chimpanzees yawn when they see another member of their group yawn, but not when it’s a member of another group.
But it’s not just primates that exhibit contagious yawning; dogs actually yawn in response to another species yawning: us. We know that dogs are outstanding at picking up on human social cues. Is it possible that through domestication and co-evolution with humans, dogs are so tuned-in to human social cues that they even yawn when we yawn out of empathy?
Some experiments seem to support this idea: one study found that dogs yawned more in response to the sound of their owner’s yawn than to another individual. But, another experiment using live models didn’t find this relationship.
Another possibility is that yawning in dogs is related to stress. Many animals yawn in response to stressful situations, and this has been found to be particularly the case in dogs. Such ‘tension’ yawns look the same as ‘sleepy’ yawns, apart from they occur with other behaviour like panting, trembling and whimpering. Therefore, it is possible that when dogs hear their owner’s voice or yawn which can be stressful to a dog (stress doesn’t have to be bad), this causes them to yawn, and this tension yawn is mistaken for a contagious yawn. It’s even been proposed that human yawns are interpreted as threatening to dogs, or at least a sign of stress, thus leading the dog to feel stressed and yawn too. This would back up a finding that shelter dogs yawn more with unfamiliar humans than familiar.
One of the reasons such different results have been found with regard to what makes dogs yawn could just be differences in the methodology these studies use. If stress causes dogs to yawn, some parts of the experiment might be more stressful to dogs, and thus cause more yawning, and it wouldn’t be due to the experimental condition itself but instead due to that condition being more stressful.
A new study attempted to address these discrepancies by explicitly looking at whether dogs that contagiously yawned more had higher levels of stress hormone (cortisol) in their saliva. They also looked to see whether dogs that contagiously yawned more were also better at a task testing their perceptiveness of human social cues: this would provide support for some degree of ‘empathy’ with humans.
In this study, the Buttner & Strasser used sixty dogs taken from the Nebraska Humane Society shelter. The dog was sat before an unfamiliar experimenter, who would then get the dog’s attention by saying it’s name, and then yawn in front of it. Each dog was also tested in a control trial which was exactly the same, but instead of seeing the person yawn, the person simply opened their mouth.
The dogs were also tested in their ability to respond to human cues by using the ‘object choice task’: a task where the dog has to find a hidden object based on where a human is looking.
Dogs yawned both in the ‘yawning’ test and in the ‘control’ test in equal number, but the dogs that yawned only in the ‘yawning’ test and not the control had higher levels of the stress hormone cortisol than the other dogs when seeing the human yawn. It doesn’t’ seem that these yawning dogs are just more stressed overall than the other dogs, because their baseline levels of cortisol were no different. Dogs that yawned more in the ‘yawning’ test rather than the control also weren’t any better at the object choice task, implying that they didn’t yawn more because they were better at picking up on human cues.
The authors suggest that how dogs see human yawns could depend on the context in which it happens. When they’re stressed, and see a human yawn, they might yawn out of stress. However, when they’re more relaxed, for example seeing a their owner yawn in their home, then perhaps they interpret it as sleepiness instead and display a contagious yawn for other reasons. Dogs will need to be tested in more ‘comfortable’ settings when they are more relaxed to look further at contagious yawning and see whether it is indeed related to their ability to perceive human social cues.
Reference
Buttner, A. P., & Strasser, R. (2013). Contagious yawning, social cognition, and arousal: an investigation of the processes underlying shelter dogs’ responses to human yawns. Animal cognition, DOI 10.1007/s10071-013-0641-z
Photo credits
Children yawning: Guy McCullough
First yawning dog: Matt Chan
Second yawning dog: Sara J S
Third yawning dog: Hillary Hartley