London’s novel is the story of Buck’s transformation from a pampered pet to a fierce, masterful wild animal, and this transformation naturally means that the canine protagonist gradually separates himself from his human masters on his way to achieving a final independence. Nevertheless, The Call of the Wild ultimately offers an ambiguous, rather than negative, portrait of Buck’s relationship to humanity. It suggests that while some human-dog relationships can be disastrous to the dog’s welfare, others are mutually beneficial, and a natural love can develop between dogs and their masters. The negative side of the man-dog compact is embodied in Hal, Charles, and Mercedes, whose inexperience, stubbornness, and general incompetence bring disaster not only on themselves but also on their sled dogs. The trio’s failure to understand the laws of the wild ultimately leads to the death of every one of their animals—except, of course, Buck, whom John Thornton saves. It is Thornton, whom Buck loves intensely, who embodies the better way in which humans and dogs can be partners, where each looks out for the other’s welfare. Buck’s visions of primitive man and his faithful dog suggest that this relationship is ultimately more primitive than civilized, and that there may be a natural bond between men and their dogs that predates modern society. Nevertheless, the story ultimately demands that even this bond be cast aside and that Buck seek his own way—suggesting that for the truly masterful animal, the greatest of dogs, having a master is only a temporary condition.

The opening of the novel sets up a contrast between two worlds: the sunny, comfortable world of Judge Miller’s estate, where Buck lives in spoiled, lordly contentment, and the harsh, frigid world of the Klondike, where he is dragged against his will. The judge’s world, as his title suggests, is defined by moral and legal codes, while the world of the Klondike is governed by a very different law. In the cold North, might makes right, and one must be willing to fight if one wishes to stay alive. Strength, not justice, is the central value. Buck learns this lesson from two events. First, he is beaten with a club by one of his kidnappers until he learns obedience, an event that teaches him about the power of violence and about the need to give in when threatened by a superior force. This reality constitutes the law of the club, and Buck learns the law of the fang when he arrives in Canada and watches one of his fellow dogs, a female dog named Curly, torn to pieces by a pack of huskies. “So that was the way,” he thinks to himself. “No fair play. Once down, that was the end of you.” These are the rules that Buck learns to live by and excel at in order to eventually become a king whose rule is defined by the “law of club and fang.”

In writing his novel, Jack London was profoundly influenced by the writings of these two nineteenth-century thinkers. Darwin, the founding father of evolution theory, taught that life in the natural world consisted of a constant struggle for survival, in which only the strong could thrive and produce offspring. This “survival of the fittest,” as Herbert Spencer, an English philosopher, termed it, was the engine that drove evolution. The world that London creates in The Call of the Wild operates strictly according to Darwinist principles in its brutality and amorality—only the fit survive in the cruel landscape of the Klondike.

Nietzsche was a German philosopher who preached the doctrine of the “will to power” as the driving force behind society. Moral considerations were meaningless, he declared, and all members of humanity were either masters, driven to dominate others, or slaves, driven to submit. London transposes this scheme to the animal world, using Nietzschean language repeatedly to describe Buck's quest to achieve mastery and dominion over his enemies, from Spitz to the animals he hunts in the forest to the Yeehat Indians who kill Thornton. Buck is clearly a canine version of Nietzsche's superman. He is an Alexander the Great among dogs, since his will to power drives him to excel. Similarly, the audience celebrates his victories, not because he is moral but because he is mighty.