The team of ten dogs was unhitched, and Buck, with his own harness, was put into the sled. He had caught the contagion of the excitement, and he felt that in some way he must do a great thing for John Thornton.

What does the harness represent?

Buck’s will to survive life in camp
Buck’s desire to return to the wild
Buck’s obedience to serve Thornton
Buck’s lack of trust for mankind