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 – the ancestors of dogs.
This muscle allows dogs to lift up their inner “eyebrow”, which makes their eye look larger. This makes them look more like childlike and also rather sad – the puppy dog eyes look.
It really does make dogs more appealing to us. In 2013, Juliane Kaminski at the University of Portsmouth and colleagues videotaped dogs interacting with strangers at a shelter to see what made them more likely to be adopted.