For decades, scientists have been struggling to understand why exactly pets appear to look like their owners. It's one of those abstract, niggling questions to which we all assume we'll never really find an answer. Well, wonder no longer. A group of Japanese scientists led by Sadahiko Nakajima, a professor of Psychological Science at Kwansei Gakuin University, may have finally discovered why it is that dogs seem to take on the traits of the human that they own.
The causal link between a dog's appearance and their owner's appearance have been studied for a surprisingly long time. Several studies, including one conducted by Nakajima himself in which people matched, "portraits of unknown purebred dogs with their owners," have proven that "the popular belief in dog–owner physical resemblance is empirically valid." In other words, that sneaking suspicion you get that the rotund fellow with no hair looks exactly like his English pitbull is actually scientifically appropriate.
For this most recent study, though, Nakajima and his team hoped to understand which physical characteristics people zero in on to make the connection between dogs and their owners. In the study, 502 undergrads in Japan were shown two test sheets, each of which consisted of 20 dog-human pairs shown side-by-side. The human faces and dog faces were edited to be equal in size, “from the vertex [highest point of the forehead] to the chin.” One sheet included 20 real life dog-person companions; the other included randomly assigned pairs. Both sets of pictures included an equal number of male and female owners and excluded mutts (for some snobbish reason).
But wait, there's more! The 502 undergrads were divided into separate groups. Each group's test sheets were designed in one of five ways. The first was no-mask, in which each photo contained the full picture of both dog and owner; Eye-mask covered the owner's eyes with black rectangles; mouth-mask covered the human's mouths with a similar rectangle. Next came Dog-Eye-Mask … bet you can guess what that did. And finally, eye-only captured solely the eyes of both owner and dog. In designing the pictures in separate ways, Nakajima hoped to pinpoint how people are able to accurately pair a dog with it's owner using no other criteria except physical traits. The cool thing is, he may have accidentally figured it out.
When the results came back, Nakajima and his team discovered that participants given the no-mask, mouth-mask or eye-only photos were able to accurately pair owners with their dogs more than 70 percent of the time. Meanwhile, those judges who were given photos that obscured either the dog's eyes or the human's eyes were much less successful at matching real-life pairs.
As Nakajima himself pointed out, "Since all of the human models were Asian dog-owners, they all had similarly dark-colored eyes. Instead, it’s clearly something that’s being conveyed in the shared look about the eyes of dogs and their people [that helps strangers form the connection]." So, when whoever it was first coined the phrase, "the eyes are the window to the soul," they may have accidentally been right on the money.