What is startling in this book is how the man believes that because he is intelligent, he can reason out any problem that may come up in his journey across the frozen landscape. He has no respect for nature. He is smug and superior in his assumption that he could not possibly be bested by nature. The dog has an inherent respect for nature and acts instinctively.
While the dog is perceived by the man as a simple, dependent creature, he is actually far superior to the man in this story. Obviously if the man had more respect for nature he would not venture out in sub-zero weather as unprepared as he is in the story. He would also have more respect for the dog and his very keen instincts.
London uses this story to criticize the arrogance of man. Though man has been gifted with the ability to reason, this gift often works against man by allowing him to ignore his instincts. In this book, the man has "reasoned" that he is intelligent enough to protect himself from the elements as he travels across the Yukon Territory.
However, the dog is relying on his instincts. The dog knows that it is too cold to be out. He knows to bite away the ice from his fur after being in the water, though the man does not know to keep his glove on. The dog is reluctant to leave the fire, but the man assumes he'll be fine after the brief warm-up.
The dog knows to shrink away from the man when the man has decided to burn the dog. His instincts warn him of the danger; instincts the man has been ignoring in himself. Finally, the dog knows that he can survive by curling up and using his own body heat, while the man makes himself worse by fighting with the fire.