First things first – I would like to note that I could not read this research article without yawning (though my dog seemed entirely unaffected).
To all dog owners out there – researchers have long been aware of how closely attuned domestic dogs are to human moods. Is it possible that this extraordinary connection, developed over thousands of years of dog-human co-evolution, extends to the phenomenon of contagious yawning?
In humans, yawning appears to have a social component; more empathetic humans tend to be more susceptible to yawn contagion, and contagious yawning emerges alongside the capacity for empathy and a theory of mind in early human development. However, contagious yawning isn’t unique to humans – researchers have observed it in many nonhuman primates and dogs as well, to varying extents. But do animals exhibit contagious yawning for the same reasons humans do? In a recent study published in Animal Cognition, researchers Buttner and Strasser set out to determine the impetus behind this phenomenon in dogs.
When they began their research, Buttner and Strasser had two possibilities in mind. One, dogs might indeed exhibit contagious yawning as a form of social interaction with humans. On the other hand, contagious yawning might actually be a form of stress yawning. Many animals, including dogs, yawn in response to stressful or uncomfortable situations. We humans can easily mistake a stress yawn for a sleepy yawn, and maybe that works the other way as well: dogs might mistake a sleepy human for a stressed one, then get stressed, and yawn in response.
The researchers used 60 shelter dogs in an experiment to determine whether each would yawn in response to a human yawning, in comparison with a control trial in which a researcher simply opened and closed her mouth. The researchers also evaluated the social-cognitive prowess of each dog – they presented each dog with a choice of two containers (one with a treat, one empty) and then gestured and looked pointedly at the treat-containing box. Dogs more closely attuned to human signals would choose the correct container more frequently, thus giving an indication of the dog’s social-cognitive ability. The researchers also estimated each dog’s stress level by measuring the levels of cortisol, a stress hormone, in a sample of each dog’s saliva. This experimental setup would, ideally, allow the researchers to determine possible links between social cognition, stress levels, and contagious yawning.
As it turned out, the results weren’t so simple to interpret. Only 12 dogs seemed to exhibit contagious yawning (that is, they yawned in response to a yawning human, but did not yawn in the control trial), and there was no overall trend of contagious yawning. These dogs did not score any better on the social-cognitive test than the other dogs, but they did have elevated cortisol levels following the experiment (but not beforehand.) From this information, Buttner and Strasser concluded that apparent contagious yawning in dogs was probably a result of stress, not empathetic social interaction. The 12 dogs that showed contagious yawning probably perceived the human yawning as a sign of stress, thus increasing their own stress levels and causing them to yawn in response.
So, next time I see my own (very spoiled) mutt yawn, perhaps I should give her a tummy rub.
I wouldn’t want her to get too stressed out.
Buttner, Alicia, and Rosemary Strasser. “Contagious yawning, social cognition, and arousal: an investigation of the processes underlying shelter dogs’ responses to human yawns.” Animal Cognition, May 2013 (published online). DOI 10.1007/s10071-013-0641-z.