Quote 46
This first theft marked Buck as fit to survive in the hostile Northland environment. It marked his adaptability, his capacity to adjust himself to changing conditions, the lack of which would have meant swift and terrible death. It marked, further, the decay or going to pieces of his moral nature, a vain thing and a handicap in the ruthless struggle for existence. (2.22)
While Buck’s adaptation involves learning many new things, it also involves unlearning some old traits. In some ways, adaptation destroys parts of Buck’s initial character.
Quote 47
His development (or retrogression) was rapid. His muscles became hard as iron, and he grew callous to all ordinary pain. (2.24)
Buck’s adaptation takes its root in the physical changes made to his body.
Quote 48
Later his feet grew hard to the trail, and the worn-out foot-gear was thrown away. (3.17)
The adaptation to pain is a necessary step on the way to Buck’s change.