Question No. 1. "The documentary hypothesis (DH) (sometimes called the Wellhausen hypothesis, after Julius Wellhausen, though he did not invent it), holds that the Pentateuch (the Torah, or the Five Books of Moses) was derived from originally independent, parallel and complete narratives, which were subsequently combined into the current form by a series of redactors (editors). The number of these is usually set at four distinct schools, but this is not an essential part of the hypothesis."
This and answers to others of your questions found at "documentary hypothesis" on Wikipedia.org.
As to why Genesis is still relevant, your last question, consider that R. Crumb, the creator of the Fabulous Furry Freak Brothers, has a new graphic novel out that is the first 50 chapters of Genesis. That's hella relevant!
Give the â��contributions�� Spinoza and Astruc made to this theory.
How does Davis refute this theory?