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Dogs and modern gray wolves share a recent wolf ancestor from which dogs were domesticated. Noting that dogs tend to have darker irises than gray wolves do, Akitsugu Konno et al. presented facial images of dogs with a range of iris colors to human participants, who rated the dogs' personality traits and their own attitudes toward the dogs. On the basis of their findings, Konno et al. concluded that the dog-wolf iris pattern may be an effect of human selection for a positively perceived trait during domestication.