Brown Eyes In Dogs – Why Are They Dominant?

June 6, 2024
Photo: A Chocolate Lab smiles gently at the camera.

Ever wonder why more dogs have brown eyes than blue? Sure, you see dogs with blue eyes here and there, but they’re often so striking because they’re such an anomaly. According to the American Kennel Club, 92% of dog breeds have brown eyes. So it begs us to wonder: Why do most domestic dogs have brown eyes?

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The Eyes Have It: From Wolves to Dogs

It’s well-known that most dog breeds were domesticated from wolves. Interestingly, wolves typically have yellow eyes, not brown like most of today’s dogs. No, they usually gaze at us with deep brown eyes. And apparently, it’s because we prefer that eye color that they’ve evolved to be that way!

A recent study by Konno Akitsugu from Teikyo University’s Department of Animal Sciences in Japan investigated why dogs mostly have brown eyes while their wild ancestors do not. The researchers compared the eye coloration of gray wolves and domestic dogs, confirming that dogs generally have darker and more reddish irises than wolves.

Human Influence On Dog Eye Color?

Ethologists suggest that wolves’ light-colored irises are adaptive, and help with communication in the wild. Lighter eyes make their pupils more visible, which helps wolves, as cooperative hunters, share what they’re looking at and their level of arousal with their pack. So, why did domesticated dogs lose this trait?

The research team hypothesized that humans might have bred dogs to have darker eyes because it makes them look more like ideal companions, and matching in human eye traits. This idea draws from the fact that human babies have larger pupils, and it’s those larger pupils that remind us of those ‘puppy dog eyes’ we all swoon over. Similarly, darker eyes in dogs would help them have the same effect and could make them appear more friendly and approachable.

Their hypothesis suggested that dogs with darker eyes were perceived to have better, more desirable personality traits.

Testing the Hypothesis

To test this theory, the researchers collected photos of various dogs with different coat colors and eye shades. They edited the images so that only the dogs’ eyes and muzzles were visible, creating pairs of images with natural and lightened eye colors. These images were then shown to 142 Japanese volunteers, who rated the dogs on traits like friendliness, aggressiveness, intelligence, and maturity.

The results were consistent across two studies: dark-eyed dogs were perceived as friendlier, more puppy-like, and more desirable to interact with than light-eyed dogs. This suggests that dark eyes in dogs send a non-threatening and inviting signal to humans.

Featured: A Terrier puppy with blue eyes looks at the camera.

Evolutionary Implications

The findings suggest that during domestication, humans may have subconsciously selected dogs with darker eyes because they perceived them as friendlier and better companions. This selection process could explain why most domestic dogs today have brown eyes, unlike their wild wolf ancestors.

In essence, the soulful brown eyes of our dogs today may be a result of evolutionary changes we humans drove, as our preferences transformed wild wolves into our beloved furry best friends!

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