Throughout this chapter, Buck begins to adjust to the new ethic, which requires intense self-reliance. The old Buck is a creature of civilization, one who would die “for a moral consideration”; the new Buck is more than willing to steal food from his masters. His transformation reflects the influence of Darwinian natural science and philosophy on Jack London’s novel. Charles Darwin, whose 1859 book The Origin of Species proposed the theory of evolution to explain the development of life on Earth, envisioned a natural world defined by fierce competition for scarce resources—“the survival of the fittest” was the law of life and the engine that drove the evolutionary process. In The Call of the Wild, Buck must adjust to this bleak, cruel vision of animal existence as he realizes that the moral concerns of human civilization have no place in the kill-or-be-killed world of the wild. What order does exist in this world is instead the order of the pack, which we observe in the way the other members of the team help train Buck as a sled dog. Even within the pack rivalry surfaces, however, as the emerging antagonism between Spitz and Buck demonstrates.

But London emphasizes that Buck does not merely learn these Darwinian lessons; they are already part of his deep animal memory. Buck may be a creature reared in the comfort of the sunny Santa Clara Valley, a domestic pet and a descendant of domestic pets, but his species roamed wild long before men tamed it. As the novel progresses, Buck taps into this ancestral memory and uncovers hidden primal instincts for competition and survival. The term for this process is atavism—the reappearance in an animal of the traits that defined its remote ancestors. Atavism is the key to Buck’s success in the wild—he is able to access “in vague ways . . . the youth of the breed . . . the time the wild dogs ranged in packs through the primeval forest, and killed their meat as they ran it down.” London suggests that primitive instincts do not die in the civilized world; rather, they go into a kind of hibernation. Such a reawakening of instincts certainly occurs in dogs, but the novel suggests that it also occurs in men. Given the right circumstances, any being can return, like Buck, to the primitive, instinctual life of his ancestors.