when London describes the world of the primitive man , he says the most noticeable thing about it is fear. What does he mean by this ?why would that be true ? Why isn't Thornton's world filled with fear ?

One is fearful when one lacks knowledge. Primitive man is unable to know much of what is true to modern man or to even a man who is scientific and has some knowledge. Thus, when one confronts the environment of a London story about the Yukon, there is much on cannot know because of the uncertainty of the way in which Nature reacts. Nature is an unknown and men often try to confront it and not really live with it. Thornton, on the other hand, has much experience which he translates into a comfortable existence with that nature. While his life is not always easy, he is generally in turn with Nature. However, his ultimate end happens because of the greed and the sinfulness of men.