A gene for religion?

That our biology permits religion is obvious. The question of whether religion gives a Darwinian advantage to the individual having an hypothetical religious gene is a good question.
Gene-based Group selection is a very dubious idea. A gene which would be good for the group but bad for the individual would have troubles remaining in the gene pool since it would be competing against alleles that are superior to itself for a long time until it succeed to infect enough individuals to permit its group related advantage to show up.
I think it is better to first look at selection at the level of the individual/gene. Second, to look if a meme-based theory would be a good theory, and only last if some more exotic theory (like the group selection theory) would permit to explain what the more solid theories above could not explain.
First, it seems that everybody has genes that are compatible with religion. 200 years ago, virtually everybody was religious. In many countries, especially those where science education is not well developed, virtually everybody is religious. People succeeding to put their faith in doubt while being in a religious surrounding are very rare. Charles Darwin is one of them but it took him tenth of years of research and thinking. A luxury that most people could not afford at that time.
I think that the genes we have which enable religion are (i) genes for asking oneself questions and for looking for answers (I.e. genes promoting understanding of one’s surrounding. Those have obvious advantages at the individual level). (ii) genes for gullibleness in children (if you do not believe your father when he tells you that crocodiles are dangerous, you will die before to be able to reproduce). The first gene (i) is a powerful aid for the individual but it has limits in its power to reach the right explanations for what happens around us due to the lack of time that individual have to collect the right evidences. Most people are too busy trying to survive and reproduce. As a result, an individual with such a gene will understand some stuffs and have wrong hypothesis to explain other stuffs.
Now, coherent systems explaining what most people cannot (or could not) explain (love, death, the sun, the rain, disease, mental illness, …) will naturally grow due to (i) and will be passed on to the kids due to (ii). Additionally, some features of these explanatory systems are very self-reinforcing: it is not good to question the system (St-thomas story in the new testament) or it is not good not to follow the system (hell) and it is good to follow the system (heaven) and you should not mix with people not believing in the system (you should not associate with a non muslim, food interdiction that make sharing a meal with a member of another believe system difficult,…).
Hence such systems are good memes (survival of the idea for the mere sake of the survival of the idea itself) that can easily occupy individual’s minds.
Losing one’s religion may come with one or more of the following: scientific instruction (evidences), contact with non-religious individuals (incentive), probably a sufficient "IQ * time-to-think" product (necessary resources) and/or presence of good non-religious alternatives to typically religious advantageous features (such as the possibility to belong to a community) .
In a nutshell, I am not convinced that a religious gene evolved because it permitted to believe in god. I think it evolved despite its side effect of permitting to believe in god.