This book goes into the Darwinistic past of religion and how it has changed into what it is today.  They start out with prehistoric societal religions that held the groups together, and made them sacrifice themselves for each other.  They then go into how early religions built on each other by taking narratives and festivals.  They go into how the major religions of today started forming.  Finally they get into how the current nationalism is a form of religion without calling out a specific deity (think manifest destiny).  I really like the book and it makes me think about how the foundations of religion are group cohesiveness and the ability to drive people to the greater good of the group over the good of the self.

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