Dogs may be known for their skills at catching sticks, but new research shows that are just as adept at catching our yawns. The result probably comes as no surprise to dog-owners but it's the first time that it's ever been demonstrated under experimental conditions.
Yawning is famously contagious - if one person does it, the chances are that someone nearby will start too. A variety of back-boned animals yawn, but until now only three species are known to catch them from each other - humans, chimps and stumptail macaques. The new study provides the first evidence that yawns can be contagious in species other than primates, or that one species can catch a yawn from another.
Ramiro Joly-Mascheroni at Birkbeck University discovered the behaviour watching how 29 different dogs interacted with a stranger. During a series of trials, the unfamiliar experimenter would call the dogs by name, establish eye contact and then either yawn loudly or silently open their mouths.
Twenty-one out of the twenty-nine dogs - 72% in total - yawned at least once when the experimenter yawned. But not a single one of them yawned when the experimenter merely opened their mouth. This stark contrast strongly suggests that the dogs were actually 'catching' the human yawns. In fact, the 'infection' rate of 72% is far higher than the rates at which other animals pass yawns to each other. Chimps only catch yawns about 33% of the time, and humans do so about 45-60% of the time.
The fact that the dogs didn't yawn in response to any old mouth movement ruled out the possibility that they were just reacting to general mouth movements, or to the presence of an unfamiliar human. It's possible that once the dogs had yawned once by chance, the experimenters were displaying subtle cues that encouraged them to do so again. But that would only have increased the total number of yawns and not the dogs that did so.
Why would a dog catch a human yawn? It's not that the experimenters were just really boring; Joly-Mascheroni suggests that it's more likely because dogs have a high capacity for empathy. Over the course of domestication, we have selectively bred dogs to be good companions and modern domestic canines are well-known for their ability to read subtle cues from their owners. They will follow the pointing of a finger or the direction of a gaze, and some can even imitate the behaviour of their owners.
Some studies have also suggested that empathy - the ability to put yourself in someone else's shoes - also underlies the contagiousness of yawning in humans. Some studies have shown that people who score more highly in tests of empathy are also more susceptible to catching yawns, while autistic children who have problems with empathy are immune to it.
Another possibility is that the dogs may even have learned to catch yawns through their experiences with their human owners.
A third and slightly more leftfield explanation is that the yawns were a sign of mild tension or stress. Not all animal yawns indicate tiredness - monkeys sometimes yawn during conflicts and it's possible, though perhaps unlikely, that the dogs viewed human yawns as a confrontational signal. This theory seems unlikely given that the control experiment didn't trigger any response, and at least, it should be easy to disprove by repeating the study while taking some physiological measurements of the yawning canines.
It will also be interesting to see if dogs catch yawns from each other. If this behaviour is indeed an side effect of the skill that domestic dogs have evolved for reading human signals, it may be that they are more sensitive to human yawns than those of their own species. Alternatively, it could be that the contagiousness of yawns evolved as a way of communicating within social groups of a single species and has since transferred to the partnership between man and hound; if that were so, dogs should be more sensitive to each other's yawns.
Those are questions for another time. For the moment, I have learned that reading and writing about yawning for a good half-hour makes you very, very tired. I wonder how the researchers actually managed to get anything done...
Reference: Biology Letters doi: 10.1098/rsbl.2008.0333
Image: by authors