"With me the horrid doubt always arises whether the convictions of man’s mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey’s mind, if there are any convictions in such a mind?"
These are the words of the most notorious Evolutionist in all of history. Charles Darwin, typically credited with having invented (or "discovered", if you're that way inclined) the modern story of Evolution. Ironically, despite being the religion's founder, he was also one of its harshest critics. Many of the flaws he found still hold up today.
The above quotation is so powerful, it's almost like it was written by C.S. Lewis. As it happens, C.S. Lewis genuinely did make a similar argument: "Supposing there was no intelligence behind the universe, no creative mind. In that case, nobody designed my brain for the purpose of thinking. It is merely that when the atoms inside my skull happen, for physical or chemical reasons, to arrange themselves in a certain way, this gives me, as a by-product, the sensation I call thought. But, if so, how can I trust my own thinking to be true? It's like upsetting a milk jug and hoping that the way it splashes itself will give you a map of London. But if I can't trust my own thinking, of course I can't trust the arguments leading to Atheism, and therefore have no reason to be an Atheist, or anything else. Unless I believe in God, I cannot believe in thought: so I can never use thought to disbelieve in God."
The logic is sound. Although some simple things can be replaced with others, such as using a boot as a flower pot, it's usually extremely ill advised to perform a task with something for which it was not designed. But in Evolution, the brain wasn't designed at all.
Evolutionists do tend to raise the objection that though they don't believe the brain is designed, they don't believe it's completely random either. But ultimately the problem is, in their religion, the brain was not designed to think. The absolute best Evolutionists can say is that the human brain is as capable of arriving at truth claims as an animal. Namely, we can come to correct conclusions if the correct conclusion helps us to reproduce.
But the reality is even this does not guarantee a correct conclusion. All kinds of beliefs might keep us alive whether true or false. For example, an arachnophobe might incorrectly assume all spiders are venomous, thus avoiding all spiders at all costs. This belief is incorrect, but is close enough to the truth that these people will not be as likely to pick up a black widow.
Interestingly, it is this very fact that Evolutionists appeal to in an attempt to explain the existence of religion. As the story goes, religious values ensured the unity of certain people groups, aiding their continued survival. In other words, human brains are very unreliable because we may hold quite vehemently to false beliefs if those false beliefs provide some kind of survival advantage. But if we are so susceptible to such lies, how do we know we aren't loaded to the brim with them?
Because Evolution literally removes the foundation for humanity's reasoning ability, Evolution can never be considered a reasonable belief. By contrast, belief in an omniscient God who has designed us to bear His image, has given us the right to subdue Creation, and has even gone so far as to command us to test all things and hold on to that which is good (1 Thessalonians 5:21), it is entirely safe to say that Christianity can be reasonable.
Because of all this, all worldviews are ultimately circular. What you believe about the origins of your brain will, or at the very least logically should, determine how you believe you can use it. For a Christian, it is consistent to believe we can use our brains to discover the truth, but for an Evolutionist, such a claim is entirely inconsistent. Thus it is far more reasonable to be a Christian than an Evolutionist.