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.
Dogs were shaped during the course of domestication both in their behavior and in their anatomical features. The domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. A muscle responsible for raising the inner eyebrow intensely is uniformly present in dogs but not in wolves.
This allows dogs to create what the researchers call “expressive eyebrows” and to “create the illusion of human-like communication” as the muscle movement allows dogs’ eyes to “appear larger, more infant-like and also resembles a movement humans produce when they are sad”.
Previous studies have shown how such canine expressions can appeal to humans, but this research from the UK and US shows there has been an anatomical change around dogs’ eyes to make it possible.