What purpose/role does the dog play in the story? Why would the author include the dog as part of his tale about the man?

The dog

The dog represents pure instinct, a trait necessary for survival in the harsh Yukon. Unlike the man, who requires the products of intellectual civilization--warm clothing, matches, maps, thermometers--the dog simply uses its own natural advantages--fur, a keen sense of smell. Perhaps more importantly, the dog has an instinctive understanding of the cold. It knows that such conditions are dangerous and unsuitable for traveling; when its feet get wet, it instinctively bites at the ice that forms between its toes. This sense of instinct preserves the dog as opposed to the man--it even knows instinctively when the man is attempting to kill it (to warm his hands in its carcass). Although the dog cannot create a fire for itself, or even hunt down food in the wild so well, its instinct keeps it alive and allows it to find the nearby camp of men--"the other food-providers and fire-providers