Oh, wow! I once wrote an article about how religions would evolve over time but I did it for the purposes of science fiction role-playing games. I told people to roll the dice for random events such as religious fusions, schisms, modifications, etc. and the dreaded time when an evil, sinister offshoot of a religion ends up swallowing its forefather and becoming the dominant religion, haha! Maybe I should make that into a hub some time.