In "The Yellow Wallpaper," how does the wallpaper function and evolve as a symbol?

In literature yellow is symbolic of evil.  In "The Yellow Wallpaper" there is, of course, ambiguity about the source of the "evil" as the reader is uncertain whether the main character is, indeed, overwrought or whether her husband tries to convince her that she is ill.

The confining room, much like the confinements of the woman's society, produces the evil as the woman is forced to be captive to either her husband's demands or to the conflicts within her.  She struggles to tear away the wallpaper, to break free of the confinements of either her own mind or the suppression of the male-dominated society.

Eventually, she becomes obsessed by the symbol of her terrible confinement and is reduced to insanity.