How do London's descriptions of the dog reveal its purpose and function in "To Build a Fire"?

The dog, who is perfectly suited to its environment, reflects the role of heredity, instinct, and natural selection in the ability to survive. It functions as the creature who has adapted to nature, in contrast to the man, and whose instinct makes it the winner in the "survival of the fittest."

On his trek to another camp, the man "plunges" in and out of the large spruce trees, following a faint trail on a day which the old timer at the previous camp has warned him not to travel, and certainly not to travel alone. But the dog, a big, native husky,  

...knew that it was no time for traveling. Its instinct told a truer tale than was told to the man by the man's judgment.

Since the man has previously been out in two cold snaps, he mistakenly believes that he is always capable of dealing with the cold. Unlike the dog, he ignores the signs that the cold in which he treks this time is much more severe than it has been on his other trips. While the man has learned to be wary of springs that run underneath the snow lest he wet his feet in the frigid temperatures and suffer severe frostbite, he underestimates the danger of the severe cold, which allows no margin for error in building a fire. Instead, he merely notices this cold:

Once and a while the thought reiterated itself that it was very cold and that he had never experienced such cold.

When he removes his mitten as he pulls out his lunch, the man is amazed at how quickly he feels the cold. He "chuckled at his foolishness" of not first building a fire, but he does note the numbness in his fingers. He notices that his toes are beginning to numb as well, yet his arrogance still prevents him from comprehending the danger he faces.

Later on, when he hurriedly tries to start a fire, he unwisely does so beneath snow-covered branches. With the ensuing heat, the snow melts and puts out the fire. The man's nemesis, the brutal cold, causes his fingers to freeze so much that he is unable to gather twigs fast enough and strike a match before frostbite sets in.

Thus, the man is defeated by nature because of his delusion of self-sufficiency. On the other hand, the dog possesses no such delusions, as its instincts signal to it what is dangerous. So, while the man lacks the means to survive by himself, the wolf-dog and its centuries of natural adaptation equip it for survival. Seeing the dog angers the man as he realizes how much better equipped this animal is than he in the brutal cold.

Furthermore, the dog quickly senses danger and leaps away from the man, who would kill it to use his body to warm himself. After the man freezes to death, the dog catches the scent of death and moves away. In a brief time, it turns and trots up the trail to the camp it knows has other fire providers, acting only out of self-preservation.