What physical and mental changes does Buck experience throughout the novel?

At the beginning Buck is a well groomed yet pampered animal.  He has the run of the property and although pampered, he is muscular and fit from hunting.  After he is taken by force from his home by a cruel man and shipped to Alaska, he becomes sick at first and then he becomes fearful of the "club" and angry at everything and everyone.  As the action continues Buck learns to survive by "doing what he needs to do to survive."  He eventually kills the Spitz and becomes the lead dog.  Eventually Buck is bought by Thornton.  It is with Thornton that Buck learns to love man and commit to complete loyalty.  As Buck and Thornton become closer they set up camp and Buck begins to wander into the "wild."  He meets a she wolf, and is torn between his natural instincts and his loyalty to Thornton.   When Thornton is killed by the Indians, Buck goes crazy and kills many of them before some escape.  At first Buck doesn't know what to do and he stays at the camp with the body of this human he had learned to love unconditionally.  In the end, Buck becomes the strong and independent leader of the pack of wolves and eventually the young wolves begin to show signs of carrying on his linage.