Also, any gene that contributes to denialism allows an otherwise preposterous meme to increase in frequency as long as the resulting behavior increases biological fitness. The individual simply denies that the meme is untrue, behaves as if it were, and benefits from the elevated fitness. While general intelligence and denialism are inversely related, the two are not directly related. A highly intelligent individual can become a denier, though this more rarely occurs.  It is worth noting that while denialism can have a genetic origin, there are other reasons someone might become a denier. For instance, a psychopath may deny climate change because he or she does not care what happens to the world or anyone else in it. However, it is fallacious to assume that all such deniers are psychopaths, and in fact, most of them probably are not. Only about 1 in 25 people in the United States suffer from anti-social personality disorder, and far fewer suffer from this malady in less individualistic cultures, such as those in East Asia.  One can see how a religious adherence to ideas can be beneficial to the individual by imagining, for instance, the behavioral result of denying overpopulation.
Ironically, if the world ever became atheist and then if scientific evidence for the existence of God became available, scientists would hypothetically have trouble convincing a mass of deniers. More sadly, violent individuals might then commit acts of terrorism against individuals who do not ascribe to atheism. The point here is that the alternatives to be denied, sometimes referred to as heresy, are not constrained by "objective reality". They are constrained by those ideas that reduce biological fitness or undermine the integrity of the system.