Back in the 1980's (lost the reference) an evolutionary biologist named Alexander made a very convincing argument for group-selection being an exceptionally strong force in human evolution.
(Note: normally, 'group-selectionist' arguments are considered very weak because selection acting at the level of the individual is so much stronger than at the level of the group. For example, all explanations of adaptations being "for the good of the species" are group-selectionist and have been discredited. The consensus is that "GS" explanations should only be employed when selection at the level of the individual is inadequate, e.g. explaining the evolution of altruism). However, Alexander points out that GS may be very important in the evolution of human civilization because conflict between groups (and cooperation within groups) was SOOOO important to survival of individuals.
I think religion is an example of a social phenomenon that has evolved in parallel forms in ALL human civilizations becuase it serves as such a strong cohesive force within human social groups. Groups with a religion had an extra unifying element in their structure. You don't just risk your life fighting for your group, but for a GOD who will take care of you if you die.
All human societies in history evolved some sort of religion,
and all religions share common premises:
1. a moral code of conduct (evolutionary function: diminishes intra-group conflict, stabilizing social structure)
2. an explanation of some kind of afterlife - re-incarnation, heaven, whatever - (evolutionary function: stabilizes the pysche of individuals seeking 'purpose' in their life)
3. a quick and easy answer to all the great unknowns of life, i.e. "God did it" (why are we here? what purpose does life serve? etc. etc. (evolutionary function: stabilizes the pysche of individuals struggling with the meaning of life )
4. postulates omnipotent being(s) as a source of teleological guidance for all life processes (evolutionary function: stabilizes the pysche of individuals by reducing their individual responsibility for higher order problems of the earth that, by default, are the responsability of humans *IF* they are the most intelligent beings and there is no God).
In human evolution, groups with religion probably out-competed groups without religion because they were both more unified in purpose, and they were less uncertain about the finality of death so they were more willing to do battle.
Bottom line: religion probably served an evolutionary function at one time or it would not be so ubiquitous in human societies, BUT IT DIDN'T EVER HAVE TO BE *true* TO SERVE THIS FUNCTION.
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