According to a study published on Wednesday and cited by AFP and Agerpres, the domestication of dogs has contributed to the change in the color of their eyes.

The eyes of dogs have become clearer than those of their close relative the wolf, and in the course of evolution they have acquired a brown shade that is more friendly and less threatening to humans.

“The iris color of dogs is darker than that of wolves, and this dark color has a positive effect on human perception of dogs,” according to a study by researchers from the Department of Zoology at Teikyo University in Japan.

Humans naturally selected for dogs with darker eyes, and this selective pressure would have favored animals whose eyes were “perceived as friendly,” according to a study published Wednesday in the journal Royal Society Open Science.

The domestication of the dog, which is descended from the gray wolf, happened gradually, 50,000 – 15,000 years ago. Today, most canines related to the wolf have a light yellowish iris with a dark pupil in the center.

Exploring the domestication of man’s best friend

In contrast, the eyes of the roughly 30 dog breeds selected for the study have large, dark irises with a tendency toward red, making it difficult to distinguish the pupils. This difference is believed to be important in the exchange of views between humans and their faithful companions.

This exchange, which the dog knows how to use to attract the attention of its master, leads, for example, to the production of oxytocin, identical to that resulting from the exchange of views between mother and child. A recent study showed that in the case of dogs, this interaction is facilitated by the development of facial muscles, which allow them to modulate the expression of the gaze, unlike wolves.

But why does a darker iris make a dog cuter in human eyes? The Teikyo researchers rely on studies conducted on primates and, in particular, humans, in which a dilated pupil is associated, for example, with positive emotions, unlike a constricted pupil.

More importantly, a large pupil will also be unconsciously associated with a juvenile, therefore vulnerable and harmless being – as in children, whose pupil size decreases with age. When a dog’s iris is dark and therefore indistinguishable from the pupil, people get the impression that they are seeing a very large pupil.

According to the study, a dog with a dark iris is perceived as “weak and in need of protection.”

What researchers discovered when studying how people perceive dogs’ eyes

The researchers tested this theory by showing people images of 12 dogs in two versions: one with their eyes closed and one with their eyes open. Participants were asked to rate the personality of each animal from friendly to less friendly.

They were also asked if they would like to interact with or even adopt each dog. The operation was repeated with the second cohort of participants.

“Dogs with their eyes closed in the images were perceived as more friendly and youthful,” the study concluded. But while this feature made interaction easier, it wasn’t enough to make people want to adopt.

The Teikyo University researchers acknowledged that their study had some limitations, such as “familiarity,” which suggests dogs with their eyes closed were preferred simply because there were more of them, or because the tests were conducted on a limited number. the number of dog species compared to all existing ones.

“This is the first study to analyze the difference in eye color between dogs and wolves,” lead author Akitsugu Konno told AFP. But “factors other than human preferences may contribute to darker eyes in dogs,” he added, hoping further research on the topic “will confirm the universality of this phenomenon.”