Regarding the protagonist, I would definitely say that rather than portraying free will, he is completely under nature’s thumb, meaning that his every move is predetermined, destined if you will.
Throughout the story, as mentioned earlier, determinism of the man’s fate is portrayed through nature’s indifference, which she shows mercilessly in different ways.
For example, in the end, he desperately tries to start a fire and warm himself up, but no matter what he does or how hard he tries, a hidden innuendo states that one cannot avoid fate, and that man is completely submissive to the greater power - nature. And from a naturalistic point of view, we can see that the story follows several of ‘the naturalistic ideas’. For example, determinism over free will, the indifference of nature, instinct over intellect, characters in the lower class. However, there is one thing about this story that I think kind of clashes with naturalism, and that is his stubborn will of surviving. Wouldn’t a naturalist say that fighting is useless since fate is inevitable anyway?
As I mentioned earlier, throughout the story, the man struggles with nature’s ruthless destruction of the man’s poor attempts of survival. At the end of the story when the dog understands that the man is dead, he runs to '...where were the other food-providers and fire-providers.' When the man died, we can see that he had no control of his life whatsoever. He tried so many things to stay alive, but in reality he had no chance, he was only delaying his impending the inevitable, as mentioned earlier.
In this story, it is quite clear that instinct is the superiority. The man uses his flawed intellect, which makes him an underdog. The dog, however, uses his instincts, and that may be one of the major reasons as to how he managed to survive the bone-shattering weather.