He was surprised at the eagerness which animated the whole team and which was communicated to him; but still more surprising was the change wrought in Dave and Sol-Leks. They were new dogs, utterly transformed by the harness… The toil of the traces seemed the supreme expression of their being, and all that they lived for and the only thing in which they took delight. Read the excerpt from The Call of the Wild, and answer the question that follows.

Which theme from The Call of the Wild is reflected in the excerpt? What does the excerpt suggest about that theme? Your response should be no less than 150 words.