Alvin Plantinga has developed a very compelling argument that contends that evolution makes naturalism self-defeating. Let’s look at a summary of the argument and then we’ll look at a more comprehensive defense.
If philosophical naturalism is true, our intellectual faculties (how we think rationally) evolved solely with reference to what gives us genetic fitness, not with reference to true belief.
If our intellectual faculties evolved solely with reference to genetic fitness and not with reference to true belief, then our intellectual faculties are unreliable.
If our intellectual faculties are unreliable, then any output of our intellectual faculties (including philosophical naturalism) is unreliable as well.
Therefore, philosophical naturalism is false.
Premise 1 says that philosophical naturalism entails that there could not have been any guidance of the evolutionary process in terms of our intellectual faculties. They are entirely the product of evolutionary conditioning, without any guidance by God. The theist alternative says that evolution did create our cognitive faculties, but that this process was guided by God. Plantinga puts it like this, “Now according to traditional Christian (and Jewish and Muslim) thought, we human beings have been created in the image of God. This means, among other things, that God created us with the capacity for achieving knowledge…And the above evolutionary account of our origins is compatible with the theistic view that God has created us in his image. So evolutionary theory taken by itself (without the patina of philosophical naturalism that often accompanies expositions of it) is not as such in tension with the idea that God has created us and our cognitive faculties in such a way that the latter are reliable…”[i] However, this is primarily an argument against naturalism and not for theism. So even if this were false, philosophical naturalism would still be self-defeating. But, the Imago Dei ( image of God) represents a way in which it can be turned into an argument for the existence of God and not merely an argument against naturalism.
Premise 2 is the main source of controversy for this argument, although it is fairly easily supported. Given that evolution is not concerned with truth, but with adaptive behaviour, we could easily have evolved intellectual faculties that have propensities to believe false things. As long as those propensities are adaptive (they increase our genetic fitness), they’ll become part of what we regard as rationality. It is strange that this claim is deemed controversial (indeed, many of Plantinga’s responders focus on this claim). Many of Plantinga’s responders denied that our evolutionary conditioning will fail to yield true beliefs to any significant extent. Yet evolutionary psychologists are always busy making claims of the sort that Plantinga has in view. For example, a common evolutionary explanation for religion, is that it developed because it was adaptive for our primitive ancestors to see agency and purpose behind everything that happened. If we hear a rustle in the bush, it is more adaptive for us to immediately assume it is a predator or some other hostile agency, than for us to assume that it was just the wind. If we assume that it’s a predator, we get out of the way, and even if there was nothing, it hasn’t disadvantaged us to get out of the way for nothing. Yet, if we assume it is the wind, it may actually be a predator, and we’ll be killed (and not pass on our genes). In other words, the cost to our genetic fitness of being credulous in this way is low, but the cost of being skeptical and dismissive is high. This is why, as Peter Millican says, we tend toward “promiscuous teleology” – we see purpose behind everything. People who advance this little “just-so story” usually don’t believe in religion. Indeed, it is often meant as a way to explain religion away. It is an evolutionary account of why we have false beliefs. And if religion is false, then this just-so story shows that evolution can encourage false beliefs on a large scale ( proving Plantinga’s point). This results in an awkward position for naturalists who are trying to deflect Plantinga’s argument. Either they have to admit that religion is true in some way, or they have to admit that evolution can encourage false beliefs. Religion is there, it is ubiquitous, and it is traceable to natural tendencies and patterns of reasoning about the world, which find their origin in human nature. It doesn’t matter if you accept the just-so story above. On naturalism, the tendency to reason in ways that favour religion has evolved, but religion is also false on naturalism. If naturalists claim that religion is false, then they have to admit that evolution conditioned us to reason in ways that don’t lead to truth (which would prove premise 2). Or religion is true. Either way, the theist wins.
Premise 3 doesn’t seem to be in need of much defense. If our intellectual faculties are unreliable, then any belief that we arrive at through our intellectual faculties is going to be unreliable. If we have good reason to doubt our intellectual faculties, then we also have good reason to doubt any belief they produce.
[i] Alvin Plantinga, introduction to Naturalism Defeated?:Essays on Plantinga’s Evolutionary Argument against Naturalism edited by James Beilby (New York: Cornell University Press, 2002) 2-3