Religion and Evolution of Average Ego

Is the history of religion a window into the particular form of the average ego as it evolves over time? Or is this just the surface appearance changing while the structure of egoing remains fairly constant?
If the history of religion does reflect/drive changes in the patterns of average ego, what can we learn from the shift from Catholicism to Protestantism, in particular the shift from emphasis on a single universal (catholic) church to "everyman with his own Bible and his own interpretation".
For example, I believe that the rise of fundamentalisms world-wide is an attempt to deal with reasonable insecurities in the face of rapid technological and social change. But do any of the fundamentalisms change the pattern of egoing (what is constrained/what is able to flow and grow)?