A while ago, I wrote a paper for school on Alvin Plantinga’s evolutionary argument against naturalism and defended it against the most common objections that had been brought against it at the time by atheistic philosophers. Plantinga is an important modern philosopher even from a non-Christian standpoint, and the fact that he is an orthodox Christian has made him an important voice for the faith. Seemingly drawing from some inspiration from earlier thinkers like C.S. Lewis, Plantinga has made a bold argument that naturalism, the belief that matter and nature is all that there is, coupled with the modern theory of evolution actually ends up giving a reason to reject belief in naturalism. To put it simply, combining naturalism with evolution is self-defeating.
Here, I will attempt to explain his argument and stay away from too much technical language or philosophical notation. I think his argument can be understood and contemplated by laymen and prove to be quite useful.
To understand what Plantinga is getting at, there are two basic things that need to grasped: How we come to form beliefs and how evolution purportedly gave us that ability.
It is pretty obvious that human beings do this: We think. Not only that, we take in information primarily through our senses. Our sense experience coupled with our ability to think about these experiences, along with other things such as math and logic, enable us to form beliefs about reality. These beliefs may be wrong, to be sure, but this is how we form them in the first place. On a lesser level, even animals can form “beliefs” in this way regarding their environment, though obviously their cognitive abilities are not quite the same as our own. Without getting into issues of epistemology, this broad picture can be generally accepted. Let’s call all this thinking and sensing our cognitive faculties.
Now we normally assume that our cognitive faculties are fairly reliable unless we have good reason to think otherwise. When I walk down the road and see a bush, I generally assume that my belief that there is a bush is accurate without any hand-wringing. However, any number of factors could lessen my confidence in my sensing and thinking. For example, let’s say that I was really far away and/or I have really poor eyesight; these could be reasons for me to doubt my belief in the existence of this bush. Or, perhaps, I was really drunk that day and now thinking back on it, I cannot be confident that my senses accurately told me that there was a bush (this is all hypothetical since I do not drink 🙂 ). Or maybe I thought it was a real bush but someone tells me that it is actually a fake bush that they created so that the area would look nice. So on and so forth. The important thing to remember is that, absent these problems (or “defeaters”), I am perfectly justified in believing that my cognitive faculties are operating in a way that gives me the truth.
Now let’s turn to the current theory of evolution. Though the theory has been modified over the years, it still remains true that it centers around survival of the fittest. All life came from single celled organisms that, through random mutation and natural selection, diversified to all the different kinds that we see if and when those mutations proved beneficial for survival and subsequent reproduction. This includes human beings and our cognitive faculties discussed above. The important thing to keep in mind is that the only thing that matters to natural selection is whether or not a particular trait is helpful for survival in a given environment.
If you’re wondering why any of this is important, here is where it gets interesting: If you add the belief of metaphysical naturalism, then you have to believe that evolution is an ultimately unguided process. There is no intelligent direction involved. However, if this is the case, Plantinga points out that there is no reason to believe that evolution gives us cognitive faculties that are reliable in giving us truth. Now why would he say that?
Let’s think again about evolution as an unguided process. As I said above, natural selection only “cares” about fitness. However, we can easily imagine scenarios where it may be more conducive for survival to have wrong beliefs. For example, let’s say that some early humans developed a belief that scorpions are dangerous because they shoot lightning from their tails. This would be a false belief, but if it helped them avoid poisonous scorpions more so than the average person, this would enable them to survive. This is not to say that wrong beliefs are always better for fitness but only that it is perfectly conceivable that they are at least sometimes better. Ultimately, natural selection doesn’t give a hoot about whether or not a particular belief is true but only that such a belief helps an organism survive. In fact, given naturalism and evolution, it is doubtful that the content of beliefs, right or wrong, matter in the first place because natural selection is only concerned about behavior. There would seem to be no clear link between the content of belief and behavior, a view called epiphenomenalism.
Here’s the kicker: If it is true that unguided evolution does not discriminate between cognitive faculties that produce true beliefs and ones that do not, then if unguided evolution is true, we have no reason to believe that our cognitive faculties are the former. Some beliefs we form may be true and some beliefs we form may not be; natural selection only cares about the ones, if any at all, that encourage behavior that helps with survival. Therefore, believing in naturalistic, unguided evolution leads us to seriously doubt the reliability of our cognitive faculties in giving us truth. If this is the case, then we have good reason to doubt every belief produced by those cognitive faculties… including both naturalism and evolution. Naturalism plus evolution ends up producing its own defeater by undercutting our confidence in our cognitive faculties. As Plantinga puts it, the probability that naturalism plus evolution has given us cognitive faculties aimed at truth is either low or inscrutable.
It is important to note that Plantinga is not arguing against evolution itself, stating clearly that it is perfectly compatible, broadly speaking, to believe in both evolution and theism. What is being addressed is the combination of naturalism and evolution, which is pretty standard for naturalists these days. If Plantinga’s argument is sound, then naturalists have to either abandon naturalism, abandon evolution, or abandon both. Not surprisingly, few are willing to do any of these.
There are a host of objections other philosophers have brought forth against this argument, and I do not have the space to address them all here. This is meant more as an introduction to hopefully motivate curious people to read about it more. I personally think the argument is a good one and one that has made some atheist philosophers uncomfortable. It is perhaps not as easy an argument to summarize for the layperson such as, say, the kalaam cosmological argument, but it is nonetheless an important one to discuss with naturalistic atheists.