what is the theme of this story?

There are a few themes that you can consider. I am partial to animal instinct winning over human hubris and knowledge. Though the man is hardly an "intellectual," he exercises intellectual properties more than instinctive ones. He uses complicated tools (matches) to build a fire; he understand how cold it is through temperature readings; he identifies where he is (Henderson Creek, the Yukon) through language on a map. The dog, on the other hand, is pure instinct. It remains warm through its fur coat or by burrowing into the snow; it has an innate understanding of the cold and its dangers; it could not point out its location on a map, but it knows by scent where to find the nearby camp with men. In the Yukon, instinct is far superior to intellect. The man's intellect backfires on him. His ability to light the matches with his numb fingers suffers in the extreme cold, and both his fingers and the matches are examples of man's naturally selected advantage of intellect: man has fingers to operate tools, and his larger, more complex brain allows him to create such tools. The dog is much wiser, aware that the cold is too dangerous for them; it even knows when the man is trying to deceive it somehow (he wants to kill it and bury his hands in its warm carcass). Accordingly, only the dog survives, and though it may not be able to take care of itself fully, it instinctively knows to go to "the other food-providers and fire-providers" in the nearby camp.