A pause seemed to fall. Every animal was motionless as though turned to stone. Only Spitz quivered and bristled as he staggered back and forth, snarling with horrible menace, as though to frighten off impending death. Then Buck sprang in and out; but while he was in, shoulder had at last squarely met shoulder. The dark circle became a dot on the moon-flooded snow as Spitz disappeared from view. Buck stood and looked on, the successful champion, the dominant primordial beast who had made his kill and found it good.
These words constitute the final paragraph in Chapter III, describing the climactic battle between Buck and Spitz. The paragraph marks the moment that Buck comes into his own by vanquishing and killing his great rival, and then taking Spitz’s place as the team's lead dog. He has left his life as a pampered pet far behind—now he is “the successful champion . . . the dominant primordial beast.” Throughout the novel, London suggests that life in the wild is defined by a struggle for mastery, and the Buck-Spitz duel is the central example of this struggle, the moment when Buck establishes himself as a master of the kill-or-be-killed ethic of the wild.