What motivates Buck to save John Thornton?

Buck's decision to save John Thornton is deeply rooted in his loyalty and love for him. Throughout the story, Buck evolves from a domesticated pet to a creature of instinct, but his bond with Thornton represents one of the purest forms of love and loyalty he has experienced. After enduring the harsh realities of life in the wilderness and the brutal treatment from previous owners, Buck finds in Thornton a sense of genuine care and respect that had been lacking in his previous relationships.

This loyalty is exemplified in several key moments in the narrative where Buck's instincts and emotions converge. Thornton treats Buck as a companion rather than just a tool for labor. As a result, Buck forms a deep emotional connection with Thornton, which culminates in his heroic act of saving Thornton from danger. This action is driven not by the need for adventure, a sense of obligation, or the desire to return to civilization, but instead by the profound love and loyalty Buck has developed towards Thornton, demonstrating how powerful and motivating these emotions can be in times of crisis.