I believe the evidence is pretty conclusive that, like most human conditions, belief in God probably has a strong genetic component [in addition to a strong environmental component]. The following are what I consider the strongest evidence:
- Autism, which has been shown to have a strong genetic component, is an excellent predictor of atheism, even after controlling for other variables such as gender, IQ, education, religious attendance, and interest in math/science/engineering
- Women are much more likely than men to believe in God, even after controlling for many other variables including lower rate of autism
- Personality tests, such as MBTI and the Empathizing-systematizing scale, are good predictors of belief in God, and such personality characteristics have been shown to have a genetic component
- Scientific studies, especially those of twins (comparing identical vs. fraternal, adopted and non-adopted), have concluded that 30-55% (depending on the study) of the variation in belief about God was heritable.
Because there is a right and a wrong answer to the God question (i.e., God either exists or he doesn't), it follows that some people, although we don't know who, must have genetic advantages and disadvantages when it comes to correctly answering it. That has some interesting and unnerving implications.
You might be fooling yourself if you think your lack of belief in God is rational. There's a distinct possibility that you're like a blind person who doesn't believe the moon exists because you can't see it, hear it, or feel it. Maybe you have an innate advantage of not sensing things that aren't there, or maybe you have an innate disadvantage in detecting certain things that are. Maybe you naturally have a difficult time processing evidence that isn't concrete. Or maybe your genetics make you naturally inclined toward theism, which might help explain why you sometimes feel like you're fighting against a natural urge to embrace the spiritual.
You might be fooling yourself if you think your belief in God is rational. There's a distinct possibility that you're like a person with schizophrenia believing [non-existent] people are spying on you, because your hallucinations seem totally real. Maybe you have an innate advantage in detecting things that other people can't, or maybe you're wired to sense things that aren't actually there. Maybe you're naturally more gullible than others. Or maybe your genetics make you naturally inclined toward atheism, which might help explain why believing in God is an especially difficult struggle for you.
Regardless of one's beliefs about God, recognizing a strong genetic component should humble us and make us even more careful not to be dismissive of theological views we don't share. Everyone experiences the world differently, and what may seem obvious to some might be nearly impossible for others to grasp.
How do you know that, if you had someone else's genetic makeup, you wouldn't believe (or lack belief in) the same things as them? And how do you know that your genetic makeup isn't one that inhibits your ability to discern the truth about God? Those are difficult questions that I think all of us should consider very seriously.
Fortunately, the other side of the coin is that the evidence reveals a similarly strong non-genetic component. Thus, everyone possesses the ability to believe or not believe in God, examine the evidence and arguments for themselves, and hopefully come to the right conclusion -- even if it might seem more difficult and unnatural for some of us.
Whatever weakness we might have, it's probably also someone else's strength. We can take full advantage of that, whether it's by applying the Ensemble Model of Religion or just by humbly and receptively listening to other people, keeping in mind that the truth isn't necessarily in the same direction as our inclinations lead us.
"The way of a fool is right in his own eyes, but a wise man listens to advice." (Proverbs 12:15)