Human selection has resulted in dogs evolving more expressive faces. They have a facial muscle for making the “puppy dog eyes” that melt many peoples’ hearts that does not exist in wolves ...

In fact dogs, but not wolves, have a specific muscle that helps raise those brows. Here’s an example of the look in a talking-dog video that nearly 200 million people have watched online.

They found that the dog breeds—including a chihuahua, a labrador, a bloodhound, a German shepherd, a Siberian husky and a mutt—all had a small, specialized muscle called the levator anguli ...