London's story is an excellent example of naturalism, a philosophy in nineteenth-century literature that did not recognize man's ability to control or determine his own life. Man was presented instead as a biological creature who reacts to whatever natural force he experiences.
In developing London's theme of naturalism in this story, the dog's role is to provide contrast with the man. The dog's behavior is instinctual; he survives the killing cold because his natural instincts control his behavior in this environment. The man, however, is a thinking creature. His attempts to survive by using his intellect fail. Also, unlike the dog, the man is not physically suited for the environment in which he finds himself. His fate is determined by natural forces beyond his control. This is seen most dramatically in the story's conclusion when the man, before finally freezing to death, runs blindly and ineffectively through the snow.
The dog, as a representative of the natural world, is not developed with a personality. The dog is an animal reacting instinctively as an animal. Getting his feet wet, he chews away the ice. Fearing the tone in the man's voice, he runs from him. Sensing the man's death and the absence of fire, the dog returns to camp. The dog does not think or feel. He survives.