Human preferences for a friendly face may have driven the evolution of dog eye color, researchers have suggested.
Ever since dogs were domesticated, some time between 15,000 and 50,000 years ago, people have – whether consciously or not – selected specific traits in their dogs.
Among them, people seem to have a penchant for puppy dog eyes. Scientists have previously found that dogs have developed specific facial muscles which enables them to draw a sad expression, which causes a nurturing response in humans and thus gives such dogs an advantage.
Now research suggests that humans may have also influenced dogs’ eye color. A study by scientists in Japan found that dark eyes are more common in domestic dogs than their wild relatives, and that people perceive dogs with dark eyes as more friendly.
“I speculate that lighter irises have some evolutionary advantage for wolves, but domestication lost this selective pressure and darker eyes emerged in some primitive dogs,” said Akitsugu Konno, the first author of the research, from the Teikyo University of Science.
The team says dark eyes may have been favored by humans later, possibly unconsciously, during the domestication of wolves to dogs.
However, Konno noted that the later development of particular breeds could also have influenced the eye color of dogs: for example, the blue merle coat color seen in breeds including shelties and border collies is associated with blue eyes.
Writing in the journal Royal Society Open Science, the team described how they compared iris color in 22 images of gray wolves of different colors and from different locations, and images of 81 domestic dogs, and found that the latter tended to be darker and redder . eyes.
The researchers then created 12 pairs of images, with one image of each pair showing a domestic dog with light eyes and the other showing the same dog with dark eyes. A selection of these pairs were shown to 76 people who were asked to rate the dogs for various personality traits and how much they would like to interact with or keep the dog.
The team found that dogs with dark eyes were rated higher for friendliness than light-eyed dogs and were perceived as more easy-going, sociable and dependent, and less aggressive, intelligent and mature. Similar results were obtained when the survey was repeated with another 66 participants.
“We speculate that a darker iris makes it more difficult to discern the size of the pupil and thus gives the illusion of a large pupil, which is associated with our perception of being more baby-like,” Konno said.
The researchers add that the association of dark eyes with immaturity may influence people to protect and care for such dogs, although the study found that eye color itself was not directly related to whether participants wanted to interact with the dog. not continue
“In general, dogs with dark eyes may have evolved the trait largely as a way to send non-threatening gaze signals to humans,” the team writes.
