What aspects of the novel can be perceived as it evolved into a major literary form?

A novel must involve a story that includes characters,
themes and conflicts.  There is a always a plot that follows a main character (or
characters) through events that require the character(s) to learn something and change
or, conversely, not change and endure the consequences.

For
me, one of the most distinguishing features of a novel is the author's use of voice. 
How is the story narrated?  A novel must always be a story told by some narrative
voice.  Even in the third person -- an omniscient, objective voice -- there is still a
perspective on the action.

When the voice is first person,
the narrator is also the main character, and this provides one of the unique
storytelling perspectives and author can take.  Think of Huckleberry
Finn or David Copperfield or Catcher In the
Rye.  Distinct voices telling stories in first-person narrative really give a
novel a powerful point of view in telling a story, and serve as an important aspect of
the novel as a major literary form.