Answer:
Buck is willing to compromise morality for survival
Excerpt (you forgot to include it in your question):
To remedy this, [Buck] ate as fast as they; and, so greatly did hunger compel him, he was not above taking what did not belong to him. He watched and learned. When he saw Pike, one of the new dogs, a clever malingerer and thief, slyly steal a slice of bacon when Perrault's back was turned, he duplicated the performance the following day, getting away with the whole chunk. A great uproar was raised, but he was unsuspected; while Dub, an awkward blunderer who was always getting caught, was punished for Buck's misdeed.