Ever since humans first domesticated dogs, we’ve been molding them – from their bodies down to their temperaments. Now, new research has suggested human actions may have even gone so far as to inadvertently steer the evolution of our pooch pals’ eye color.
A team of scientists from Japan analyzed images of 22 grey wolves and 81 domestic dogs (including 35 major dog breeds) and found that dark irises were more common in the latter. They believe this finding has something to do with what we find less threatening to look at.
“I speculate that lighter irises have some evolutionary advantage for wolves, but domestication has lost this selective pressure and darker eyes have emerged in some primitive dogs,” said first author Akitsugu Konno, speaking to the Guardian. These darker eyes, the researchers suggest, may then have been unconsciously favored by humans, perceiving them as less wolf-like and thus friendlier.
The team tested this theory out by showing a group of 76 people 12 pairs of images: one of a domestic dog with dark eyes and another of the same dog, but with light eyes. Participants were then asked to rate the dogs on certain personality traits, such as how friendly, independent, and trustworthy they were. They were also asked how much they would like to interact with the dog, or even keep it.
The survey revealed that dark-eyed dogs were rated more highly for friendliness, trustworthiness, and sociability, and lower for aggression, intelligence, and maturity. These results may lean into something that many of us do – thinking of our dogs as children, particularly when they give us so-called “puppy eyes”, something that’s enhanced by a darker eye color.
“We speculate that a darker iris makes it more difficult to distinguish the size of the pupil and thus gives the illusion of a large pupil, which is associated with our perception of being more infant-like,” said Konno. As a result, we’re more likely to want to care for them and less likely to throw them out to the wolves – even when they’ve dragged their muddy paws all over the carpet or woken you up for the third night in a row.
However, the researchers do highlight some limitations to their study. The photographs used did not fully capture the diversity of either dogs or wolves, and there may well have been other significant factors influencing dog eye evolution during domestication.
Overall though, the team believes that “dogs with dark eyes may have evolved the trait largely as means to send non-threatening gaze signal to humans.”
Remember that next time they look at you innocently after destroying your new shoes – we did it to ourselves.
The study is published in Royal Society Open Science.