Here's a breakdown of why:
* Domestication to Wildness: Buck's journey is from a pampered life as a house dog to a wild, fierce wolf-dog. He sheds his human-imposed manners and behaviors, embracing the instincts of his ancestors.
* Loss of Civilization: This "progress" involves losing the learned behaviors and social skills of a domesticated dog. He becomes less obedient, less gentle, and more driven by survival and primal urges.
* A Biological Perspective: London uses evolutionary theory to explain Buck's change. He believes that our domesticated animals have suppressed primal instincts, and when those instincts are reawakened, they represent a return to a more natural state.
* Loss of Individuality: In becoming more "wolf," Buck loses aspects of his individual personality that were developed during his domesticated life. This is reflected in his growing indifference to human companionship and his increasing reliance on his primal instincts.
It's important to note that "retrogression" isn't necessarily a negative term in this context. London doesn't condemn Buck's transformation; he simply presents it as a natural and inevitable process of returning to his ancestral roots. Buck's story is ultimately about the powerful call of the wild and the primal instincts that lie within us all.