Thus IMO the authors contention that all relgions are in fact immutable. That after their creation events, there might be small adjustments to interpretation and small details, but the big dogma, no matter what it is at the time of that religions creation, remains inviolate. Furthermore, this is in sharp counterdistinction to science in which very little of the ideas set forth at any fields creation event are unchanged over time.
If you take a look at Christianity there have been many many small adjustments through time, those combined together make it a pretty different thing from the first 'set religion'. Whatever that was, because the separate authors of the Bible alone didn't create the Bible in one day, let alone the selection of texts that happened on various occasions through time, together with some editing to make sure it stays (more) coherent.
There has been as much 'evolution of content' going on when it comes to religious ideas, as there has been an evolution of psychology in the way the text are written.
The Bible in itself is already prove for this, as it shows a changing God.
