By comparing the facial anatomy of wolves and dogs, researchers showed that a unique pair of muscles in a dog’s face allows it to raise its inner eyebrow into “puppy dog eyes." Human protective instincts are triggered by a dog’s expressive eyes, and likely drove the evolution of this trait.

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By comparing the facial anatomy of wolves and dogs, researchers showed that a unique pair of muscles in a dog’s face allows it to raise its inner eyebrow into “puppy dog eyes." Human protective instincts are triggered by a dog’s expressive eyes, and likely drove the evolution of this trait.