Is atheism self-contradictory ?

[ManofYesterday]

How can a product of an unconscious natural process be reliable ?

Simple.  Organisms with unreliable minds are more likely to die out, leaving a gene pool of more reliable minds.

First, one has to define what they mean by reliable. Reliable with respect to what?
 
Under atheism, evolution is unconscious, mindless, cold, etc. It's a mechanism; and there's no consciousness behind the mechanism. What's more, it's a mechanism that didn't have to exist. The natural world could have came into being--or could have existed for eternity--without a mechanism like evolution. Evolution just happens to exist and it functions in a particular way. And the way it functions could have been different. Nevertheless, it functions in our world through mutations and reproduction. If a mutation increases a species’ chance of surviving and reproducing, then it will be passed down to later generations. A brain that is tuned for ascertaining truths and falsehoods doesn't necessarily follow from this process. For instance, a mutation could be introduced that negatively affects the cognitive faculties but nevertheless dramatically increases the survivability of the species through a different means. This would then be passed down to later generations. Or a mutation could be introduced that produces a false belief, but the false belief increases survivability. Finally, it may be that our brains are very good at things like "stay away from spiders" or "don't jump off cliffs" but they aren't good at abstract concepts like mathematics and philosophy. For example, maybe there was a mutation that increased our chances of understanding Calculus or Quantum Mechanics, but since being good at Calculus or Quantum Mechanics doesn’t increase your chances of surviving millions of years ago, it was left behind for simpler things like “don’t stay under water for too long.”
 
This is why it should be difficult for the atheist to reconcile their belief that their brains are ultimately the product of natural processes—nothing more or nothing less—and the belief that their brains are reliable for ascertaining truth.