Dogs have orbital muscles above their eyes that wolves lack. The sole purpose of these muscles is to enable the dog to emote better... to humans. Dogs also cooperate with and interpret physical cues from humans the way wolves might with their packmates only. This also means that dogs can interpret uniquely human physical cues, such as pointing with a finger, which wolves cannot.

The natural social life of the dog is the human world. Humans and dogs co-evolved to live and work together. No other species enjoys this kind of symbiosis with us to this level; the horse probably comes the closest.