I have been struggling lately with understanding the origins and purpose of religion.  I am currently listening to Richard Dawkin’s The God Delusion but also stumbled upon this string of posts by an evolutionary biologist that I wanted to share:

Explaining Religion
Explaining Religion 2: What is Religion
Explaining Religion 3: Is it Adaptive?

I am starting to differentiate the original evolution of religions from their growth and expansion.  This brings up the unit of analysis question, which these articles seem to be struggling with.  Is our unit of analysis the initial reasons that religions appeared or the reasons that they flourished, grew and still exist.  These are likely to be completely different sets of reasons.