The process of dog domestication, which has been ongoing for millennia, has seen humans selectively breed dogs for certain traits, consciously or unconsciously. One such trait that seems to be favored by humans is the appearance of a dog’s eyes.
Studies over time have shown that dogs have evolved specific facial muscles that allow them to display an expression of vulnerability, which tends to draw human affection.
Furthermore, recent research suggests that humans may have an impact on a dog’s eye color. A study conducted in Japan found that pet dogs tend to have darker eyes compared to their wild counterparts, leading to the perception that these dogs are more friendly, according to The Guardian.
People often perceive dogs with dark eyes as being amiable. “We theorized that a lighter iris was beneficial for wolves, but the process of domestication has reduced this selective pressure, resulting in some domestic dogs having darker eyes,” said Akitsugu Konno, a contributor to the study from Teikyo University of Science.
The researchers propose that humans may have unconsciously preferred dogs with darker eyes over time, during the transition from wolves to domestic dogs. Alternatively, Konno suggested that selective breeding of certain breeds could have influenced eye color. For example, the blue merle coat color, seen in breeds like the Shetland Sheepdog and Border Collie, is associated with blue eyes.
When comparing the iris color of various gray wolves with different fur colors and geographical origins to images of 81 pet dogs, the authors noted that pet dogs generally had darker and redder eyes.
Dogs with open eyes are becoming less prevalent. The scientists created 12 pairs of images, each pair featuring a pet dog with open eyes in one image and the same dog with dark-colored eyes in the other. A subset of these pairs was shown to a group of 76 volunteers, who were asked to evaluate the dogs based on various characteristics and express their willingness to interact with or adopt the animal.
The researchers found that dogs with dark eyes were perceived as friendlier, more sociable, intelligent, dependable, and less aggressive compared to dogs with light-colored eyes.
“We speculate that a darker iris makes it difficult to determine the size of the pupil, thereby creating the illusion of a larger pupil, which we associate with a more youthful appearance,” Konno explained.
The researchers also suggest that associating dark eyes with juvenile characteristics could encourage humans to care for and nurture such puppies.
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