There are apparently two academic theories regarding the composition of the present form the Torah/ Pentateuch. One is the documentary hypothesis and the other is the supplementary hypothesis.
The theories are quite similar. Essentially the documentary hypothesis is that a later source stitched together a number of exisiting sources, the Elohim, Jehovan, Priestly sources etc, (most likely either during or after the Babylonian Exile) and edited them on its compilation. The opposing hypothesis is the supplementary hypothesis which posits there was an existing primary source, the Elohim Source, which has been supplemented and edited by later additions.
The supplementary theory would appear to be consistent with the idea of how the gospels were generated with Matthew, Luke and John working of Mark with supplementary sources.
In bygone days we had the odd theologian around here, does anyone have any strong views on the documentary or supplementary theories? Does anyone know where you can find a copy of the Elohim version of the Torah online (one interesting part of this is that apparently in this version Abraham kills Isaac).