Belief Genetics

I doubt that the belief gene has been identified. (And probably won't be, people have been burned at the stake for less.)  But according to Shermer it exists in a large segment of the population.  Not always religious, but politics and religion are the most common expressions.  Probably tribe membership or authority related from an evolutionary viewpoint. 
But look around you.  Believers beget believers.  It would be hard to separate out nature vs nurture, but believers occasionally beget people who can actually read the Bible and the newspapers, or actually think about what they watch on the boob tube (for them.) One might think of them as deficient in the belief gene as the occasional green-eyed redhead is deficient in the melanin gene. 

But non-believers also beget non-believers.  I come from a family that goes back to the earliest colonists for which "He would have been mayor except he pissed off the preacher." was their characterization of most of the famous members.  "He" was usually run out of town as the original settler was run out of England. An ancestor was a General in Washington's army, but was run out of Virginia (and America) to Ohio.  

They also perhaps necessarily marry non-believers weeding out the belief gene.  My great grandmother married into the family but was an atheist, free thinker and feminist.  (late 19th Cen.)