What ultimately motivates Buck to assert himself in the pack?

Buck's motivation to assert himself in the pack primarily stems from his instinctual need for survival. In the harsh environment of the Yukon, where only the strongest can thrive, Buck quickly learns that the dynamics of the pack require him to compete for food, status, and safety. This survival instinct overpowers his previous domestic life, pushing him to embrace his primal nature. Assertion in the pack is not just about gaining dominance; it’s about securing the necessities of life in an unforgiving landscape—a key theme in Jack London’s narrative illustrating the struggle for existence in the wild. Thus, while aspects like a competitive nature or a desire to lead may play roles, the overarching drive is rooted in survival, which is paramount in Buck's transformation and evolution throughout the story.