Humans tend to prefer dogs with darker eyes, scientists have found, which could be linked to how they evolved from wolves.
Dogs evolved from their closest relatives, gray wolves. Over time, they became domesticated by humans, becoming friendlier, more used to humans and less wild than their wolf relatives. This is why dogs now make good pets, whereas gray wolves remain a wild, predatory species.
In a new study published in a Royal Society journal, Japanese researchers set out to discover why eye patterns differ in dogs and wolves and how this affects humans' acceptance of the species.
Comparing images of 22 gray wolves and 81 domestic dogs, scientists found that the irises of dogs were significantly darker than those of wolves.
"Our image analysis revealed that the iris colour of dogs was significantly darker and reddish than that of wolves," the authors said in the study. "This result is the first empirical data supporting the qualitative documentation that the 'darkbrown' eyes of dogs differ from the 'yellow' eyes of wolves."
The facial images of dogs with darker eyes were also perceived as friendly and immature by humans. In other words, these dogs were much more appealing to humans than ones with a lighter iris color.
This begged the question: did dogs purposefully evolve with dark eyes to make them more appealing to humans?
Lead author Dr Akitsugu Konno of Teikyo University of Science in Japan told Newsweek that there is no question that this difference evolved during the domestication process.
"This is the first study suggesting eye color difference in dogs and wolves," Konno said.
"Not only was there a clear eye color difference between wolves and dogs but also we found that dogs with darker eyes are perceived as more friendly and immature by humans. This finding suggests that humans may unconsciously select for dark eyes because they seem less threatening and being protected by humans, which might be more evolutionarily adaptable to domestic dogs."
According to the researchers, darker irises mean changes in pupil size are less visible. These size changes can trigger negative emotional responses in humans, the study said. Humans also tend to make conclusions about a person's personality depending on iris and pupil contrast.
There is far more research to be done in this area, Konno said.
"Dogs are living all over the world, and there is high morphological diversity. Wolves too. We should collect more and more samples of dogs and wolves. Furthermore, factors other than human preference (e.g., ecological factors, UV protection) may contribute to darker eyes in dogs. Future studies are needed to confirm the universality of the phenomenon."
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Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
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