The human physical/mental and spiritual experience and our ability to find meaning where there is little did allow religion to flourish.
Go back three thousand years to a hypothetical scenario:
One group of 10 settlements are peaceful and trade among each other.
A second group of 10 settlements not only trade goods but also spiritual belief and a common religion is founded.
The peninsula that both groups share suffers a severe drought one summer and the crops fail.
Which grouping survives?
This is indeed natural selection, but as to the genetic feedback resulting from suchlike scenarios. These types of pressures effect on the genepool is a very interesting field of study I would imagine (I wouldn't know as this is all my own ponderings).
What is an instinct in a human. Is it something we cannot deny?
Can a man keep his hand in a fire if he wants to?
Conscious thought is malleable and though I do think the weakness of humans can give an individual the propensity for religious belief. One will only find the belief that oneself is capable of uncovering. Most people are fed tradition and are trapped by its routine, and their own propensity for routine.
I for one have never been trapped by routine and have evolved my own theory of how the universe ad infinitum could work.