You and your dog might have the same eyes.
We've all seen the silly listicles of people who look like their dogs, but research suggests that these similarities are not just funny coincidences or tricks of the camera.
Japanese psychologist Sadahiko Nakajima has focused his research on dog-owner resemblance. He conducted an experiment in 2009, where he asked volunteers to match dogs with their owners simply by looking at pictures of their faces. The volunteers were able to match the dogs with the correct owners at a rate higher than could be attributed to random guessing.
Nakajima's results were consistent with the results of other previous studies, but he wanted to do more research on specific facial features of dogs and humans. He conducted another study in 2013, in which he showed volunteers two sets of photos: one of real dog-owner pairs, and one of randomly paired dogs and people, and asked them to determine which pairing was the real dog-owner pair.
Nakajima introduced several more variables, though. Different participants saw different parts of the dogs' and humans' faces. Some saw the whole faces, others saw everything except the human's eyes, or the human's mouth, or the dog's eyes. Some only saw the eyes of both.
The photos looked like this:
Nakajima found that people were able to identify the correct pairing 80 percent of the time when they saw the complete faces. Concealing the human's mouth did not significantly affect the accuracy, but concealing the eyes of either the human or the dog did.
Accuracy fell to 50 percent--equal to random chance--when participants could not see the eyes. Conversely, when they could only see the eyes, their accuracy was 74 percent--almost the same as when the whole faces were showing.
Nakajima concluded that people resemble their dogs primarily in the eye region.
This still does not answer the question of why so many dog owners look like their pets. Nakajima's explanation is simple: people choose dogs who look like them. He bases this theory on the mere exposure effect, the idea that people prefer what is more familiar to them.