How did Buck's experience cause him to change his character?

Buck is forced to adapt and change over the course of the novel in order to survive he circumstances he's thrust into. His early life is one of a cherished pet and companion. After he's stolen from his home, he is physically and violently broken into an animal forced to labor for humans. He has to adjust to human expectations and compete with the other dogs for position. In the end, Buck becomes companion and helpmate to a man who respects him and gives him love (John Thorton). After Thorton's death, Buck embrace the freedom he experiences in the wild.