Consider the concept of determinism in listing reasons why the ending of "To Build a Fire" meets the conventions of naturalism.
It would be helpful to begin the answer to this question with a reflection on what Naturalism is. The naturalists were nineteenth-century writers who went beyond realism in an attempt to portray life exactly as it is. Influenced by the work of Charles Darwin and his theories of natural selection and survival of the fittest, the naturalist writers believed that human behaviour is determined by heredity and environment. Relying on new theories in the social sciences, naturalists dissected human behaviour with detachment and objectivity. Naturalism above all presents human beings as subject to natural forces beyond their control.
It is this idea that is central to this short story. The story tells the story of one arrogant man who takes the challenge and struggle that nature presents him with too lightly and underestimates the power and immensity of the forces that nature commands. He dies as a result of this mistake. Nature is shown to be utterly indifferent to human needs and desires and above all that we are subject to natural forces beyond our control. Determinism fits in because the man in the story had an option - he could have chosen to heed the warning of the old timer from Sulfur Creek and not go out when he knew it was so cold, but he chose to arrogantly and presumptuously go out anyway. Determinism would state that therefore in a sense the man wrote his own death sentence.