Dark eyes are a prevalent feature among domesticated dogs.
Humans have a soft spot for dogs with soulful brown eyes, while their wild cousins, wolves, often sport piercing yellow eyes. A new study suggests this eye-dye preference might be rooted in our shared evolutionary history. Over time, wolves transformed into friendly pups, shedding their wild ways for cuddles on the couch. This shift also brought changes in appearance, including eye color. Wolves' bright yellow eyes, once essential for hunting in low light, became less crucial for domesticated dogs. Meanwhile, darker eye shades emerged, potentially attracting human affection. The study, published in Royal Society Open Science, suggests human preference for puppy-dog eyes may have inadvertently influenced canine evolution.
According to a release, Akitsugu Konno, a behavioral scientist at the Teikyo University of Science, and his team conducted a study to investigate the rationale behind this evolutionary phenomenon. They edited photos of dogs representing 33 different breeds, ranging from corgis to Irish wolfhounds, manipulating the eye colors to be either lighter or darker. Following this, the researchers presented these edited images to a group of 142 Japanese volunteers, predominantly consisting of students. The participants were tasked with assessing each dog based on various traits, including friendliness, aggressiveness, maturity, and intelligence.
The findings revealed that the volunteers perceived dogs with dark eyes as social and non-aggressive, giving them lower ratings for intelligence and maturity while associating them more with puppy-like characteristics.
"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," Akitsugu Konno, the first author of the research from Teikyo University of Science, told The Guardian.
"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," Akitsugu said.
"Overall, dogs with dark eyes may have evolved the trait largely as a means to send non-threatening gaze signals to humans," the team writes.