Why do you think the protagonist is referred to as "the man" as opposed to being given a name?

London uses the generic term "the man" to place emphasis on nature as the more important character. The man is pretty much a flat character. He symbolises the arrogance and weakness of humans when they do not heed nature's warnings. I suppose in this case London might be referring to white man in particular for the natives around this land would not make such foolish mistakes, "He was a newcomer! in the land, a chechaquo, and this was his first winter." As the story goes on the man's decisions are symbolic of our, in the western world, own perception of mastery over nature. If we do not heed nature's warnings we too could suffer a similar plight.