What is naturalism, and how does Jack Londons' "To Build a Fire" represent it?

Jack London is a poster boy for naturalism, and his short story, "To Build a Fire," is a good example of why.

Naturalism is an extreme form of realism, with a heightened attention to nature and its effects on humans.  Humans are animals like any other when pitted against the forces of nature.  Humans are subject to the forces of nature.

The main character in "To Build a Fire" is pitted against nature and he is vulnerable to it the same as any other creature:  disrespect it or make a mistake, and you will suffer the consequences.  In fact, in the climate of the story, man is inferior to other animals.  The character takes the environment too lightly and does not prepare properly, and there are consequences for this.