Those "Puppy Dog Eyes" You Can't Resist? Shaped by Evolution, Study Finds

You know that feeling when a dog looks at you with that look - those “puppy dog eyes” - and you can’t seem to resist? It turns out, dogs’ facial muscles evolved to fit with human preferences, according to a new study.

Scientists found a muscle responsible for raising the inner eyebrow intensely, is uniformly present in dogs, but not in wolves. The expression is similar to the one humans make when they are sad.

Researchers say the “puppy dog eyes” expression not only elicits a nurturing response from humans, but it might play a role in dog-human communication because humans are especially good at reading eyebrow expression during interactions.