If ever you overhear someone comparing you to a dog, chances are it’s not a compliment. Yes, there’s the famous loyalty of dogs, their unbridled enthusiasm for life, their boundless love and devotion, their fierce protectiveness—qualities that any of us would be lucky to possess at even a modicum of their standard manifestation in the canine. Typically, though, it’s meant as a slight and a reference to some especially animalistic aspect of our four-legged friends. That assertive woman people call a “bitch,” for instance (a term that has always struck me as being dubious; some of my kindest, gentlest companions in this world have been female dogs), or the lowlife “cur” who cheated you in that game of poker the other night.
As much as we might quibble over the virtues and vices of Canis domesticus, however, and over whether human nature is any better or worse than dog nature, even dog fanciers don’t usually want to look like a dog. The hair of a poodle, the jowls of a bulldog, the bug eyes of a pug, the wrinkles of a Shar-Pei, the profile of a collie, the street-sweeping udders of a lactating mongrel … none of these traits are considered beautiful when incarnated in our own species. Still, if we look in the mirror, each of us can expect to find a certain doggy je ne sais quoi staring back at us. Those of us who own a dog, anyway. And we don’t resemble just any old dog, either. Rather, we look somehow, in a can’t-quite-put-your-finger-on-it kind of way, like our own dogs.
It’s one of those curious observations that’s had scientists scratching their heads for decades. When shown a photo lineup of random people and random dogs, people are able to match the pets with their owners at a rate greater than chance. At first, researchers thought there must be something obvious going on here, something that boils down to a simple, perhaps implicit, heuristic. Maybe men are more likely than women to own large breeds, for example, and women to own toy breeds. Or women with long hair are more likely to own dogs with floppy ears rather than perky ears. Or perhaps obese people overfeed their dogs, and thus we’d expect fat owners to have fat dogs (a correlation that does, in fact, exist). Yet the ability to match strangers with their own dogs holds up even when these more obvious superficial characteristics are carefully ruled out by the research design.
So what is it, exactly, that enables us to correctly link owners and their dogs? That’s the mystery that Sadahiko Nakajima, a psychologist from Kwansei Gakuin University in Japan, set out to solve in a recent study published in the journal Anthrozoös. This wasn’t Nakajima’s first stab at it. In prior research, he and his colleagues had shown that research participants could match photos of owners and their dogs by facial appearance alone. People could also recognize that photos of dogs and owners that the investigators had arbitrarily coupled were fake pairs. Impressive! Still, that just told him that people are surprisingly adept at knowing which pooch goes with which person on the basis of their facial appearance. So in this latest study, Nakajima teased apart the various possibilities to find out which facial features people use to make their bizarrely accurate judgments.
Here’s how it worked. The researcher presented 502 Japanese undergrads with two test sheets. Each sheet included 20 photo sets of dog-human pairs, showing their faces together side-by-side. To eliminate extraneous factors, the photos were very basic color headshots cropped at the shoulders and shown against a plain white background. Nakajima writes that the portraits were taken earlier at a “dog-lovers’ field festival” and that the pet owners were instructed to look straight at the camera and smile slightly. Presumably these instructions worked for the dogs as well—the photos show them with the same Mona Lisa grins as their masters. These resulting 40 human faces and 40 dog faces were digitally rendered equal in size (11 to 12 millimeters “from the vertex [highest point of the forehead] to the chin”). The photos were then randomly assigned to one of those two test sheets. On one test sheet, the images included a set of 20 real-life dog-owner pairs; the other sheet featured 20 randomly matched pairs. These photo sets included an equal number of female and male human owners. It’s not entirely clear to me why mutts weren’t included (perhaps there was a bit of snobbery at that dog-lovers’ fest), but nonetheless there was still a healthy variety of breeds represented in the portraits, everything from the relatively rare Belgian tervuren to that popular pint-sized terror, the Yorkshire terrier, to papillons and golden retrievers.