Themes of the call of the wild

In The Call of the Wild, primitivity is presented as the authentic and dominant side of a being. Modernization and civilization, then, go against true nature. Primitivity is tied to ancestry and history; as Buck has dreams of mankind thousands of years before, he yearns to be a part of the wild world to which his predecessors belonged.
Suffering in The Call of the Wild is largely physical. We expect our protagonist to feel a certain level of emotional turmoil after he is taken from his home, but instead his survivalist tendencies kick in. The story becomes one about surviving physical hardships rather than dwelling on thoughts and feelings. Buck endures suffering at the hands of the wilderness (the hard conditions, the freezing cold), other dogs (both in his pack and feral), and man (always in the form of a weapon like a club or a whip). Buck’s suffering, though, is an important part of his character development. The Call of the Wild shows that whatever doesn’t kill you makes you stronger.
In The Call of the Wild, the thirst to prove himself is a large part of Buck’s transformation into a more powerful and dominant dog. While pride does play second fiddle to survival, it explains why Buck excelled instead of merely staying alive. Pride is the difference between pulling the sled and being the lead dog on the sled team, between being adequately strong and moving a thousand-pound load. While pride does add complications to life in the wilderness (such as fights with other dogs for dominance), it is also beneficial as a means of motivation.

Walked would be the participle here. as it is a verb ending in -ed.