Quote 49
Thirty days from the time it left Dawson, the Salt Water Mail, with Buck and his mates at the fore, arrived at Skaguay. They were in a wretched state, worn out and worn down. Buck's one hundred and forty pounds had dwindled to one hundred and fifteen. (5.1)
Again, we see some destruction involved in Buck’s adaptation, this time it is physical.
Quote 50
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. Murmurs of admiration at his splendid appearance went up. He was in perfect condition, without an ounce of superfluous flesh, and the one hundred and fifty pounds that he weighed were so many pounds of grit and virility. His furry coat shone with the sheen of silk. Down the neck and across the shoulders, his mane, in repose as it was, half bristled and seemed to lift with every movement, as though excess of vigor made each particular hair alive and active. The great breast and heavy fore legs were no more than in proportion with the rest of the body, where the muscles showed in tight rolls underneath the skin. Men felt these muscles and proclaimed them hard as iron, and the odds went down to two to one. (6.43)
Buck’s physical appearance goes through great changes. In order to achieve the splendor of this moment, he must first undergo suffering and deterioration.
Quote 51
Buck tightened the traces, then slacked them for a matter of several inches. It was the way he had learned. (6.51)
Buck is able to apply what he learned in the frozen North once he has left.