 Plantinga argues that combining naturalism and evolution is self-defeating, because, under these assumptions, the probability that humans have reliable cognitive faculties is low or inscrutable.He claimed that several thinkers, including C. S. Lewis, had seen that evolutionary naturalism seemed to lead to a deep and pervasive skepticism and to the conclusion that our unreliable cognitive or belief-producing faculties cannot be trusted to produce more true beliefs than false beliefs.He claimed that "Darwin himself had worries along these lines" and quoted from an 1881 letter