As everyone knows, there has been a recent spate of books attacking Christian belief and religion in general. Some of these books are little more than screeds, long on vituperation but short on reasoning, long on name-calling but short on competence, long on righteous indignation but short on good sense; for the most part they are driven by hatred rather than logic. Of course there are others that are intellectually more respectable—for example Walter Sinnott-Armstrong's contribution to God? A Debate Between a Christian and an Atheist[1] and Michael Tooley's contribution to Knowledge of God.[2] Nearly all of these books have been written by philosophical naturalists. I believe it's extremely important to see that naturalism itself, despite the smug and arrogant tone of the so-called New Atheists, is in very serious philosophical hot water: one can't sensibly believe it.

Naturalism is the idea that there is no such person as God or anything like God; we might think of it as high-octane atheism or perhaps atheism-plus. It is possible to be an atheist without rising to the lofty heights (or descending to the murky depths) of naturalism. Aristotle, the ancient Stoics, and Hegel (in at least certain stages) could properly claim to be atheists, but they couldn't properly claim to be naturalists: each endorses something (Aristotle's Prime Mover, the Stoics' Nous, Hegel's Absolute) no self-respecting naturalist could tolerate.

These days naturalism is extremely fashionable in the academy; some say it is contemporary academic orthodoxy. Given the vogue for various forms of postmodern anti-realism and relativism, that may be a bit strong. Still, naturalism is certainly widespread, and it is set forth in such recent popular books as Richard Dawkins' The Blind Watchmaker, Daniel Dennett's Darwin's Dangerous Idea, and many others. Naturalists like to wrap themselves in the mantle of science, as if science in some way supports, endorses, underwrites, implies, or anyway is unusually friendly to naturalism. In particular, they often appeal to the modern theory of evolution as a reason for embracing naturalism; indeed, the subtitle of Dawkins' Watchmaker is Why the Evidence of Evolution Reveals a Universe Without Design. Many seem to think that evolution is one of the pillars in the temple of naturalism (and "temple" is the right word: contemporary naturalism has certainly taken on a religious cast, with a secular priesthood as zealous to stamp out opposing views as any mullah). I propose to argue that naturalism and evolution are in conflict with each other.

I said naturalism is in philosophical hot water; this is true on several counts, but here I want to concentrate on just one—one connected with the thought that evolution supports or endorses or is in some way evidence for naturalism. As I see it, this is a whopping error: evolution and naturalism are not merely uneasy bedfellows; they are more like belligerent combatants. One can't rationally accept both evolution and naturalism; one can't rationally be an evolutionary naturalist. The problem, as several thinkers (C. S. Lewis, for example) have seen, is that naturalism, or evolutionary naturalism, seems to lead to a deep and pervasive skepticism. It leads to the conclusion that our cognitive or belief-producing faculties—memory, perception, logical insight, etc.—are unreliable and cannot be trusted to produce a preponderance of true beliefs over false. Darwin himself had worries along these lines: "With me," says Darwin, "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?"[3]

Clearly this doubt arises for naturalists or atheists, but not for those who believe in God. That is because if God has created us in his image, then even if he fashioned us by some evolutionary means, he would presumably want us to resemble him in being able to know; but then most of what we believe might be true even if our minds have developed from those of the lower animals. On the other hand, there is a real problem here for the evolutionary naturalist. Richard Dawkins once claimed that evolution made it possible to be an intellectually fulfilled atheist. I believe he is dead wrong: I don't think it's possible at all to be an intellectually fulfilled atheist; but in any event you can't rationally accept both evolution and naturalism.

Why not? How does the argument go?[4] 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. We just are our bodies, or perhaps some part of our bodies, such as our nervous systems, or brains, or perhaps part of our brains (the right or left hemisphere, for example), or perhaps some still smaller part. So let's think of naturalism as including materialism.[5] And now let's think about beliefs from a materialist perspective. 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. According to the usual story, electrical signals proceed via afferent nerves from the sense organs to the brain; there some processing goes on; then electrical impulses go via efferent nerves from the brain to other organs including muscles; in response to these signals, certain muscles contract, thus causing movement and behavior.

Now what evolution tells us (supposing it tells us the truth) 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 issues in survival and reproduction.

Now this same neurophysiology, according to the materialist, also causes belief. But while evolution, natural selection, rewards adaptive behavior (rewards it with survival and reproduction) 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." Taking up this theme, naturalist philosopher Patricia Churchland declares that the most important thing about the human brain is that it has evolved; hence, she says, its principal function is to enable the organism to move appropriately:

Boiled down to essentials, a nervous system enables the organism to succeed in the four F's: feeding, fleeing, fighting and reproducing. The principal chore of nervous systems is to get the body parts where they should be in order that the organism may survive … . Improvements in sensorimotor control confer an evolutionary advantage: a fancier style of representing is advantageous so long as it is geared to the organism's way of life and enhances the organism's chances of survival [Churchland's emphasis]. Truth, whatever that is, definitely takes the hindmost.[6]

What she means is that natural selection doesn't care about the truth or falsehood of your beliefs; it cares only about adaptive behavior. Your beliefs may all be false, ridiculously false; if your behavior is adaptive, you will survive and reproduce. 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.

Next, to avoid interspecies chauvinism, let's not think about ourselves, but instead about a hypothetical population of creatures a lot like us, perhaps living on a distant planet. Like us, these creatures enjoy perception, memory, and reason; they form beliefs on many topics, they reason and change belief, and so on. Let's suppose, furthermore, that naturalistic evolution holds for them; that is, suppose they live in a naturalistic universe and have come to be by way of the processes postulated by contemporary evolutionary theory. What we know about these creatures, then, is that they have survived; their neurophysiology has produced adaptive behavior. But what about the truth of their beliefs? What about the reliability of their belief-producing or cognitive faculties?

What we learn from Crick and Churchland (and what is in any event obvious) is this: the fact that our hypothetical creatures have survived doesn't tell us anything at all about the truth of their beliefs or the reliability of their cognitive faculties. What it tells us is that the neurophysiology that produces those beliefs is adaptive, as is the behavior caused by that neurophysiology. But it simply doesn't matter whether the beliefs also caused by that neurophysiology are true. If they are true, excellent; but if they are false, that's fine too, provided the neurophysiology produces adaptive behavior.

So consider any particular belief on the part of one of those creatures: what is the probability that it is true? Well, what we know is that the belief in question was produced by adaptive neurophysiology, neurophysiology that produces adaptive behavior. But as we've seen, that gives us no reason to think the belief true (and none to think it false). 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 the cognitive faculties of these creatures 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 power -58). 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.[7] So the chances that these creatures' true beliefs substantially outnumber their false beliefs (even in a particular area) are small. The conclusion to be drawn is that it is exceedingly unlikely that their cognitive faculties are reliable.

But of course this same argument will also hold for us. 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. If there isn't a defeater for that defeater—a defeater-defeater, we could say—she can't rationally believe that her cognitive faculties are reliable. 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—the belief in the combination of naturalism and evolution—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. So the argument isn't an argument for the falsehood of evolutionary naturalism; 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.

What sort of reception has this argument had? As you might expect, naturalists tend to be less than wholly enthusiastic about it, and many objections have been brought against it. In my opinion (which of course some people might claim is biased), none of these objections is successful.8 Perhaps the most natural and intuitive objection goes as follows. Return to that hypothetical population of a few paragraphs back. Granted, it could be that their behavior is adaptive even though their beliefs are false; but wouldn't it be much more likely that their behavior is adaptive if their beliefs are true? And doesn't that mean that, since their behavior is in fact adaptive, their beliefs are probably true and their cognitive faculties probably reliable?

This is indeed a natural objection, in particular given the way we think about our own mental life. Of course you are more likely to achieve your goals, and of course you are more likely to survive and reproduce if your beliefs are mostly true. You are a prehistoric hominid living on the plains of Serengeti; clearly you won't last long if you believe lions are lovable overgrown pussycats who like nothing better than to be petted. So, if we assume that these hypothetical creatures are in the same kind of cognitive situation we ordinarily think we are, then certainly they would have been much more likely to survive if their cognitive faculties were reliable than if they were not.

But of course we can't just assume that they are in the same cognitive situation we think we are in. For example, we assume that our cognitive faculties are reliable. We can't sensibly assume that about this population; after all, the whole point of the argument is to show that if evolutionary naturalism is true, then very likely we and our cognitive faculties are not reliable. So reflect once more on what we know about these creatures. They live in a world in which evolutionary naturalism is true. Therefore, since they have survived and reproduced, their behavior has been adaptive. This means that the neurophysiology that caused or produced that behavior has also been adaptive: it has enabled them to survive and reproduce. But what about their beliefs? These beliefs have been produced or caused by that adaptive neurophysiology; fair enough. But that gives us no reason for supposing those beliefs true. So far as adaptiveness of their behavior goes, it doesn't matter whether those beliefs are true or false.

Suppose the adaptive neurophysiology produces true beliefs: fine; it also produces adaptive behavior, and that's what counts for survival and reproduction. Suppose on the other hand that neurophysiology produces false beliefs: again fine: it produces false beliefs but adaptive behavior. It really doesn't matter what kind of beliefs the neurophysiology produces; what matters is that it cause adaptive behavior; and this it clearly does, no matter what sort of beliefs it also produces. Therefore there is no reason to think that if their behavior is adaptive, then it is likely that their cognitive faculties are reliable.

The obvious conclusion, so it seems to me, is that evolutionary naturalism can't sensibly be accepted. The high priests of evolutionary naturalism loudly proclaim that Christian and even theistic belief is bankrupt and foolish. The fact, however, is that the shoe is on the other foot. It is evolutionary naturalism, not Christian belief, that can't rationally be accepted.

Alvin Plantinga is John A. O'Brien Professor of Philosophy at the University of Notre Dame.

1. Reviewed elsewhere in this issue by Douglas Groothuis, in a piece covering four books dealing with atheism in one fashion or another.

2. Coauthored with Alvin Plantinga in Blackwell's Great Debates in Philosophy series (Blackwell, 2008).

3. 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.

4. Here I'll just give the bare essentials of the argument; for fuller statements, see my Warranted Christian Belief (Oxford Univ. Press, 2000), chap. 7; or my contribution to Knowledge of God (Blackwell, 2008); or Natural Selection and the Problem of Evil (The Great Debate), edited by Paul Draper, www.infidels.org/library/modern/paul_draper/evil.html.

5. If you don't think naturalism does include materialism, then take my argument as for the conclusion that you can't sensibly accept the tripartite conjunction of naturalism, evolution, and materialism.

6. "Epistemology in the Age of Neuroscience," Journal of Philosophy, Vol. 84 (October 1987), pp. 548-49.

7. My thanks to Paul Zwier, who performed the calculations.

8. See, e.g., Naturalism Defeated?, ed. James Beilby (Cornell Univ. Press, 2002), which contains some ten essays by critics of the argument, together with my replies to their objections.

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