One of the key ideas necessary to understand this excellent short story of man pitted against nature is Naturalism. As you indicate, we can definitely say that this is a Naturalist short story. The naturalists were nineteenth-century writers who in their work went beyond realism in an attempt to portray life precisely as it it. They were strongly influenced by Darwin's theory of evolution and his concept of the survival of the fittest, and they believed that human actions and behaviour is determined by heredity and environment. Naturalists exposed human behaviour in an objective fashion, and presented human beings as being under the control of natural forces much stronger than they.
We can see these ideas of Naturalism, which draw so much upon Social Darwinism and determinism, throughout this story. The central flaw in the protagonist in this story is that he completely and arrogantly underestimates the power of nature. Note how the text describes him:
He was a newcomer in the land, a cheechako, and this was his first winter. The trouble with him was that he was without imagination. He was quick and alert in the things of life, but only in the things, and not in the significances. Fifty degrees below zero meant eight-odd degrees of frost. Such a fact impressed him as being cold and uncomfortable, and that was all. It did not lead him to meditate upon his fairly as a creature of temperature, and upon man's frailty in general, able to live within certain narrow limits of heat and cold, and from there on it did not lead him to the conjectural field of immortality and man's place in the universe.
It is precisely this failing in his thinking that London shows led to this man's death. According to London, it is clear that exposure to nature in its raw power should automatically create in us a profound respect for its power and might and lead us to meditate upon our own weaknesses and inner fragility as humans.