Reposted from a previous thread -- my personal opinion about the transition from non-history to history:
Genesis 1 is totally non-history, I think the passage's elaborate structure and rhythmic/formulaic nature make that clear. New Bible Dictionary (
http://www.ivpress.com/cgi-ivpress/book.pl/code=1439) describes it as a theological hymn of praise.
Genesis 2-3 are highly mythical, that is clear from the elegant narration style, as well as the multitude of symbolic elements -- paradise garden, tree of life, tree of knowledge, forbidden fruit, serpent, fig leaves, flaming sword, cherubim etc.
Genesis 4 might be based on a historical murder, but I feel the story is also couched in semi-mythical elements (eg. the "mark" of Cain and the sevenfold vengeance).
Genesis 6-9 (story of flood) is probably based on a historical event, though the story is given elaborations (especially the elohist version). The main point is theological not historical.
Genesis 12 and onwards (abraham etc.) is definitely based on solidly historical figures and events, although retold with theological emphases.
As you can see, the "switch" from non-history to history is probably gradual, but even the so-called "historical" narratives are primarily there to teach theology, not just provide a historical account. Abraham, Moses and David are all historical figures, but their stories are told to us not as biographies (in the modern sense) but as religious/theological accounts. Remember that the Jews never considered there to be a "historical" section in their Bible -- there was only Law, Prophets and writings. The concept of "books of history" is alien to the Hebrew scriptures.