Scholars have traced the roots of many of the Old Testament stories to the ancient, pagan myths of the ancient Mesopotamian cultures. In the Fertile Crescent, the waters of the Tigris and Euphrates rivers, in present-day Iraq, gave birth to some of the worlds first civilizations.
In this early flowering of civilization, many religious myths abounded, seeking
to explain what was then unexplainable. From this context comes the oldest
complete literary work we have, the age of which we are certain, dating back at least 7,000 years. The Epic of Gilgamesh is a lengthy narrative of heroic
mythology that incorporates many of the religious myths of Mesopotamia, and it is the earliest complete literary work that has survived.
Many of the stories in that epic were eventually incorporated into the book of Genesis. Borrowed from the Epic of Gilgamesh are stories of the creation of man in a wondrous garden, the introduction of evil into a naive world, and the story of a great flood brought on by the wickedness of man, that flooded the whole world.[/INDENT]
For more see:
http://www.bidstrup.com/bible.htm
As much so as a work by some 150 authors could be, patched over, stitched, added and deleted to by e.g. Constantine and the various ecumenical councils, where various groups fought for their respective interpretations and emendations.