The "dominant primordial beast" grows stronger in Buck as conditions on the trail become rougher, and his rivalry with Spitz more perilous. Buck is careful not to pick any rash fights, but Spitz never misses an opportunity to show his teeth. One night, while the team makes camp off Lake Le Barge, Buck nestles beneath a rock. Buck leaves his spot to eat his ration, but returns to find a growling Spitz occupying his "nest." They prepare to fight, but their tussle is interrupted when hundreds of "starving huskies" attack the camp.
The "dominant primordial beast" represents Buck's innate drive to master others. The dog that stands in the way of Buck's rise to power is Spitz. And Spitz is not going down easily, as his threatening move of occupying Buck's nest demonstrates. In order for Buck to embrace his inner alpha dog, he will have to oust Spitz from his position as lead dog. The struggle for mastery of the pack begins.
The camp is in a frenzy. Perrault clubs the skeletal huskies, while the sled dogs fight against the mad canines. Three huskies attack Buck. Slashed and ripped, Buck retaliates, biting into a husky's jugular. The taste of the warm, frothy blood rouses his fighting instincts, but before he can make another move, Spitz attacks him from the side. Spitz attempts to throw Buck off his feet, but Buck steadies himself, retreating with the other dogs.
The huskies' attack magnifies the wild beast stirring within Buck. Just as the huskies are mad with the primal urges of hunger, Buck is incited to fight when he first tastes blood. His instinct to kill, or be killed awakens as Buck fights off the husky, while his will to survive surges when Spitz takes the opportunity to attack Buck. Spitz' attack here indicates that he recognizes the threat Buck poses to his status as alpha dog.
When the team reemerges from the woods the next morning, the battle is over, but the huskies have laid waste to the camp, having eaten practically everything in sight and injured almost every single sled dog. With supplies depleted and the dogs riddled with bites, François worries that his dogs have been infected with madness, (rabies), and is uncertain that they will survive the next four hundred miles to Dawson.
François's concern for his dogs' health reveals the co-dependent nature of the relationship between man and dog. François knows that his survival inevitably depends on the well being of his animals, for without them he cannot make the trek across the Klondike.
Perrault dauntlessly leads the team across Thirty Mile River's thin ice. Buck almost falls through the ice twice, but is rescued both times before he freezes or drowns. One morning at Pelly, Dolly suddenly goes mad and begins chasing Buck. François kills Dolly with an ax, but Buck is exhausted from the chase. Spitz, seeing an "opportunity," springs upon Buck, but François whips him before battle can ensue.
The thin ice alludes to the wild's treacherous quality, while Dolly's madness underlines its unpredictability. These foreboding qualities enforce nature's role in natural selection—some will survive nature's curve balls, other's will not, and survival depends on a combination of skill and luck. Spitz's opportunistic attack on Buck shows that their rivalry is escalating, and that wily Spitz will do whatever he can to stop Buck's ascent.
Buck's growing pride in his work and confidence in his inborn ability to lead drives him to subvert Spitz's dominance. Buck incites a subtle insurrection when he defends Pike against Spitz's authority. François's whip keeps order, but a showdown between Buck and Spitz is imminent as the team arrives in Dawson.
After a week's rest in Dawson, the team pushes onward to Skaguay. But there is unrest in the traces as Buck's insurrection continues. One night, Buck leads the pack in a rabbit hunt. Caught up in the chase, Buck fails to notice Spitz leaving the pack and is surprised when Spitz leaps out to snatch the rabbit. Buck barrels into him, knocking them both into the snow.
The disorder in the traces magnifies the unsettling effect of Buck's pursuit to overthrow Spitz. Meanwhile, Spitz's cunning attack on Buck signals that he will not go down without a fight. Just as only one dog can kill the rabbit, only one dog can be left standing as master of the pack.
The time has come for Spitz and Buck to face off. A silence falls upon the pack as they circle around the rivals. Buck attacks Spitz with fervor from every angle, but Spitz, an experienced fighter, fends off every assault, leaving Buck bloodied and himself untouched. Buck rushes at Spitz again, but this time clamps down on Spitz's leg, breaking it. The ravenous pack descends upon the crippled Spitz, while Buck looks on the carnage with satisfaction.
This final showdown will determine the leadership of the pack. When Buck breaks Spitz's leg, he displays his wolfish prowess and wins the canine struggle for mastery. By overthrowing Spitz, Buck not only commits his rival to certain death, he establishes his supremacy and the dominance of his "primordial beast." And note how once the other dogs sense Spitz' weakness they attack and kill him. There is no sentimentality for their former leader.