A new study claims to have answered the question of why most dogs have brown eyes, reports the Guardian. In a new paper at Royal Society Open Science, researchers in Japan make the case that humans view dark-eyed dogs as friendlier, even if subconsciously. In comparison, their wild wolf cousins tend to have lighter eyes. When humans began domesticating and breeding dogs, they evidently put their thumb on the scale of evolution by favoring animals with brown eyes. Researchers showed people's preference for darker eyes by asking dozens of study participants to rate the friendliness of dogs in photos, per Smithsonian. The subjects were actually shown two photos of the same dog, but with the eyes photoshopped to be either light or dark.
"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," lead author Akitsugu Konno of the Teikyo University of Science in Japan tells Newsweek. "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." (More dogs stories.)
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