When it comes to contagious yawning, it seems that every new study dramatically changes our understanding of the behavior. That is not too surprising given that until recently contagious yawning did not receive much attention. Contagious yawning was a curious, almost comical, human behavior with no relevance to the rest of our or any other lives. Several years ago the thinking began to change. First, contagious yawning was linked theoretically to contagious emotions (like fear), which forms the basis for empathy. With the link to empathy, all of a sudden there was a reason to study contagious yawning in humans and other animals. Empathy is one of our defining traits with implications for our evolution and applications to mental health and the functioning of society at large. Second, experiments supported the link between contagious yawning and empathy in humans, and comparative studies showed that humans are not the only species to yawn contagiously.
Last week saw two new species added to the list of species capable of contagious yawning. Ramiro Joly-Mascheroni and colleagues reported in Biology Letters that dogs yawn in response to a human yawning, and Alessia Leone and colleagues reported at the 22nd Congress of the International Primatological Society that gelada baboons yawn in response to other baboons yawning. For those keeping score, five species out of five examined show contagious yawning. The totals are, in order of discovery, humans, chimpanzees, stump-tail macaques, domestic dogs, and gelada baboons. The most interesting part is that no one has yet identified a species that has not shown contagious yawning when tested. How pervasive is this trait? We have yet to find out.
Ultimately, this comparative endeavor will be very useful in assessing empathic abilities in different species. If we can find a way to experimentally link contagious yawning with empathy in nonhumans, then we will have a behavior easily identifiable that will be directly comparable across species. The ability to compare species with a single measure would be immensely helpful in understanding the evolution of empathic abilities. These studies bring us a little bit closer to resolving centuries old debates on the uniqueness of human empathy, and that is nothing to yawn about.
— Matthew Campbell