"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?"
- Charles Darwin, in a letter to William Graham (Down, July 3, 1881), in The Life and Letters of Charles Darwin, ed. Francis Darwin (London: John Murray, 1887), Volume 1, pp. 315-16.
Darwin was no intellectual slouch. If this "horrid doubt" could have been resolved simply by testing our convictions (or more generally, our cognitive faculties from whence our convictions spring) to determine their trustworthiness then why should Darwin have this concern? There are at least two reason why Darwin's doubt can't be addressed by testing. First, and most obviously, it begs the question, since it calls on us to assume the soundness of our cognitive faculties so they may adequately serve to judge the soundness of those self-same cognitive faculties. Second, testing our convictions does not address the core issue which is not the trustworthiness of our convictions per se, but rather their trustworthiness given Darwin's hypothesis of naturalism, operating within the confines of his evolutionary theory.
I think our convictions (or beliefs) are indeed trustworthy as a result of our having been created by a rational Mind who endowed us with a share of His own rationality. Given a rational Creator and His bestowing of rationality upon humans, it's expected that our beliefs would be by-and-large trustworthy. Does naturalistic evolution likewise lead to trustworthy beliefs? Darwin doubted it. I doubt it. So does noted philospher Alvin Plantinga. He summarizes his argument in the article, "Evolution vs. Naturalism: Why they are like oil and water" from the July/August 2008 issue of Books & Culture.
The first thing to see is that naturalists are also always or almost always materialists: they think human beings are material objects, with no immaterial or spiritual soul, or self....According to materialists, beliefs, along with the rest of mental life, are caused or determined by neurophysiology, by what goes on in the brain and nervous system. Neurophysiology, furthermore, also causes behavior....[What] evolution tells us is that our behavior (perhaps more exactly the behavior of our ancestors) is adaptive; since the members of our species have survived and reproduced, the behavior of our ancestors was conducive, in their environment, to survival and reproduction. Therefore the neurophysiology that caused that behavior was also adaptive; we can sensibly suppose that it is still adaptive. What evolution tells us, therefore, is that our kind of neurophysiology promotes or causes adaptive behavior, the kind of behavior that [results in our] survival and reproduction.
Now this same neurophysiology, according to the materialist, also causes belief. But while evolution, natural selection, rewards adaptive behavior and penalizes maladaptive behavior, it doesn't, as such, care a fig about true belief. As Francis Crick, the co-discoverer of the genetic code, writes in The Astonishing Hypothesis, "Our highly developed brains, after all, were not evolved under the pressure of discovering scientific truth, but only to enable us to be clever enough to survive and leave descendents."
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Consider a frog sitting on a lily pad. A fly passes by; the frog flicks out its tongue to capture it. Perhaps the neurophysiology that causes it to do so, also causes beliefs. As far as survival and reproduction is concerned, it won't matter at all what these beliefs are: if that adaptive neurophysiology causes true belief (e.g., those little black things are good to eat), fine. But if it causes false belief (e.g., if I catch the right one, I'll turn into a prince), that's fine too. Indeed, the neurophysiology in question might cause beliefs that have nothing to do with the creature's current circumstances (as in the case of our dreams); that's also fine, as long as the neurophysiology causes adaptive behavior. All that really matters, as far as survival and reproduction is concerned, is that the neurophysiology cause the right kind of behavior; whether it also causes true belief (rather than false belief) is irrelevant.
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We must suppose, therefore, that the belief in question is about as likely to be false as to be true; the probability of any particular belief's being true is in the neighborhood of 1/2. But then it is massively unlikely that [one's] cognitive faculties... [would] produce the preponderance of true beliefs over false required by reliability. If I have 1,000 independent beliefs, for example, and the probability of any particular belief's being true is 1/2, then the probability that 3/4 or more of these beliefs are true (certainly a modest enough requirement for reliability) will be less than [10 to the -58th power]. And even if I am running a modest epistemic establishment of only 100 beliefs, the probability that 3/4 of them are true, given that the probability of any one's being true is 1/2, is very low, something like [.000001 to the 7th power].
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If evolutionary naturalism is true, then the probability that our cognitive faculties are reliable is also very low. And that means that one who accepts evolutionary naturalism has a defeater for the belief that her cognitive faculties are reliable: a reason for giving up that belief, for rejecting it, for no longer holding it. ... No doubt she can't help believing that they are; no doubt she will in fact continue to believe it; but that belief will be irrational. And if she has a defeater for the reliability of her cognitive faculties, she also has a defeater for any belief she takes to be produced by those faculties—which, of course, is all of her beliefs. If she can't trust her cognitive faculties, she has a reason, with respect to each of her beliefs, to give it up. She is therefore enmeshed in a deep and bottomless skepticism. One of her beliefs, however, is her belief in evolutionary naturalism itself; so then she also has a defeater for that belief. Evolutionary naturalism, therefore... [is] self-refuting, self-destructive, shoots itself in the foot. Therefore you can't rationally accept it. For all this argument shows, it may be true; but it is irrational to hold it.
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The argument isn't an argument for the falsehood of evolutionary naturalism; [or even, may I add, that our cognitive faculties are not, in fact, reliable] it is instead for the conclusion that one cannot rationally believe that proposition. Evolution, therefore, far from supporting naturalism, is incompatible with it, in the sense that you can't rationally believe them both.
