"If evolution is true, what roll does religion play in human adaptation and natural selection and why would humans fight, kill, invest, deprive themselves and expend vast amounts of material and energy into building giant cathedrals and embarking on lengthy missions throughout our history??? Remember, nature selects AGAINST waste and extravagance. Environmental pressures should have weeded out the "god gene" long ago, or so it would seem..." OP
Several other people have already mentioned this, but here goes....
I suspect that religion emphasizes or strengthens "herd" mentality - er, "cooperation".
In other words, if a leader wants to get his group roused to act as a single unit, whether it be warfare or hunting or building a stone monument [which would also serve as a sort of 'territory marker'...] or farming or building roads or....
You get the idea.
Anyway, using religion as a means of stimulating the whole group to pull together, would make 'Religion' a useful adaption to improve the survival rates of human groups.
Did I win? Do I get a prize???
Zid