The naturalist wants us to believe that the natural world is all that exists; we came about through evolutionary processes and our minds are one of the products of that process. Given the survival of the fittest paradigm that rives evolution, the naturalist must also assert "What your beliefs are don't matter nearly as much as what the survival value of your actions are." In fact, they do this when discussing religion all the time. Religion isn't true, they would assert, but it served an evolutionary purpose.
To use an example, picture an overweight man who is running. Now, the man may believe he has a better chance at survival if he runs because he puts his body in better shape, reduces the chances of heart attacks, and is generally more fit for the tasks of survival. However, the man may equally believe that running is an act of worship to the life-god and it drives out the fat demons that plague much of his tribe. Either belief produces the same result: the man runs and the man has an increased chance of longevity. Either belief helps him survive equally well. It doesn't matter which is true on an evolutionary worldview because evolution is all about survivability.
Reason Offers No Evolutionary AdvantageBecause all evolution cares about is the survival of the individual, reason alone offers no evolutionary advantage. In fact, evolutionary theory proves this. According to all New-Darwinian models, there was a time on the earth where there existed no rational thought whatsoever! Animals were primitive and they had no capacity to reason, yet they survived just fine. They mere responded to external stimuli and adjusted their behavior. They don't know why the water is here and not somewhere else; they simply desire water.
This is why you can get a pet dog or cat to chase a flashlight beam or laser pointer on the floor. The dog bites at it and it isn't there, yet he will continue to chase the beam! Your pet is simply responding to stimuli. They aren't thinking abstractly. A dog never wonders what it's like to be a cat!
Knowing that the earth circles the sun as opposed to the sun circling the earth gives us no evolutionary advantage whatsoever. We gain nothing in terms of the advantage to put food in our stomachs or to shelter us from the cold nights. This is because reason and responses are categorically different kinds of things. There is a difference between neural stimulation and mental reflection. The naturalist will say "All reason is is a process of neural stimulation" but C.S. Lewis argued that natural selection only operates by eliminating biologically harmful responses and increasing responses linked to better survival. He writes:
It is not conceivable that any improvement of responses could ever turn [the animal's thoughts] into acts of insight, or even remotely tend to do so. The relationship between response and stimulus is utterly different from that between knowledge and the truth known.1
Beliefs Can be Counter-IntuitiveSometimes we have to believe things that are completely counter-intuitive based on our stimulus. Exercise is a good example of this. For me, it is counter-intuitive when lying in my comfortable, warm bed to get up and put my body in a situation designed to cause strain and pain. So the desire to exercise doesn't come from external stimuli, but from our reasoning capabilities. We do the things that are counter intuitive to everything the body is telling us because we have a reasoned that that's a better way to go. It doesn't make sense evolutionary because the benefits are a long way off.
Alvin Plantinga agrees when he writes:
Fleeing predators, finding food and mates — these things require cognitive devices that in some way track crucial features of the environment, and are appropriately connected with muscles; but they do not require true belief, or even belief at all.There are many of our beliefs that lie completely outside the realm of evolutionary advantage at all. The belief that evolution is true is one of these. The problem is the evolutionist doesn't have good grounds for holding to his own evolutionary tale, since the evolutionary framework gives no grounds for holding that any of his beliefs are true. If evolution is true, then reason isn't trustworthy. How does one escape that when every belief the naturalist has is a product of evolution? Assuming naturalism is to doubt the reliability of reason itself.
The long-term survival of organisms of a certain species certainly makes it likely that its members enjoy cognitive devices that are successful in tracking those features of the environment — indicators, as I've been calling them. Indicators, however, need not involve beliefs (emphasis added).2
2. Plantinga, Alvin. Where the Conflict Really Lies: Science, Religion, and Naturalism. New York: Oxford UP, 2011. 329. Print.