Dr. Alvin Plantinga’s evolutionary argument against naturalism involves the claim that naturalism and evolution are incompatible. This claim is best refuted by examining what factors influence the structure and function of our neurology, as well as how we evaluate the truthfulness of beliefs. It will be shown that the process of naturalistic evolution is such that it necessarily creates a reliable neurology capable of holding beliefs. These beliefs, although imperfect, may be considered generally reliable and subject to additional scrutiny to determine their truthfulness. It is the a posteriori probability of truth, subsequent to empirical testing, that determines whether beliefs can be rationally held, and not the a priori probability associated with beliefs based upon individual impressions.
Plantinga’s contention is that the theory of evolution and metaphysical naturalism are incompatible. He tries to support this claim by arguing that since our cognitive faculties may be unreliable, we cannot assume that our beliefs are true. He writes:
One can’t rationally accept both evolution and naturalism; one can’t rationally be an evolutionary naturalist. The problem … 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.
According to Plantinga, the acknowledgment of an imperfect neurology precludes an individual from holding a majority of true-beliefs. His argument relies on the assertion that a neurology shaped by the forces of natural selection is reliable only in terms of adaptive behavior, regardless of whether or not the beliefs causing the behavior are true. Plantinga offers the following example:
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.
Plantinga states that our neurology is adapted only for procuring the necessary environmental items for survival and reproduction, rather than for producing true-beliefs. For example, one could reasonably argue that religion has, at one time or another, conferred a reproductive advantage to its adherents despite its falsity. Therefore, Plantinga argues that it is unreasonable to assume that adaptive behavior necessarily results from true beliefs. So, the entire argument for the incompatibility of naturalism and evolution relies on the truth of the assertion that adaptive behaviors have an equal likelihood of being either true or false. On this basis, Plantinga argues that the combination of naturalism and evolution should be rejected in favor of theism and evolution because theistic evolution is more likely to result in a preponderance of true-beliefs.
It is correct to describe our neurology as being adaptive. However, Plantinga’s argument fails because it does not recognize that the function of our neurology depends on the process by which it is formed, and not the point from which it began. In other words, both cases (theism vs. naturalism) result in adaptive evolution formed by the fidelity with which sensory neurons transduce energetic, chemical, and physical information into electrical information. This electrical information is subsequently transmitted to the central nervous system for integration and belief-formation that influences our behavior. Simply stating the presumption that God would create us in such a way that we could have knowledge is not enough. One would need to demonstrate why God’s choice of an identical process to shape our neurology would result in different a priori probability of true-belief.
It is important to notice that Plantinga never explicitly states that he believes human neurology is reliable. What he actually writes is this:
… even if he [God] 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.
Plantinga presumes that evolution shaped by a God, and evolution by naturalistic processes, are different in some way. He offers no explanation as to how the same processes under equal conditions would produce different results. The implication is that if we start with God, rather than a naturalistic explanation, the probability that a belief is a true-belief is improved. By simply restating the Christian belief that we are created in God’s image, Plantinga achieves nothing in terms of demonstrating the improvement of true-beliefs manifested by adaptive neurology under the God-evolved condition.
The processes that involve interactions between environment and organism are the same for the conditions of God-evolution and naturalistic evolution. It is these processes that determine the structure and function of our neurology, and it is our neurology that determines our belief systems. Consequently, Plantinga’s argument is essentially meaningless. He simply asserts that if he introduces God into the naturalistic explanation then he can use naturalistic evolution to justify presupposed religious dogma. This strategy is as dishonest as it is inaccurate because it introduces an untestable and unfalsifiable alternative hypothesis into an explanation (evolution) that has been deduced by the scientific method. This method makes its degree of certainty commensurate with the evidence created by evaluating testable and falsifiable hypotheses. So, when Plantinga offers an untestable and unfalsifiable alternative to naturalistic evolution, he is not really offering any explanation at all. Instead, Plantinga only succeeds in coupling rational inquiry to religious superstition. In that way, Plantinga only takes another step in constructing an infinitely expanding tautology where even the empirical methods used to evaluate beliefs are enfeebled by cleverly obfuscating the distinction between science and superstition.
Before we examine how we can come to hold true-beliefs, let’s define what we mean by the terms reality, truth (or true-belief), and neurology. When we talk about reality we are referring to ourselves and the energy, space, and matter exterior to our minds. Truth, or a true-belief, is a belief that is consistent with reality as it exists independently of our cognitive faculties. Our neurology is our cognitive faculties—the tool with which we experience the reality exterior to it.
Evolution tells us that our phenotypic traits are passed to our descendants, slightly modified, and that the subsequent variability in offspring survivability results in a change in gene frequency through differential reproductive success. So, then, what determines the variability in survival? Organisms need to interact with their external environment in order to procure the items they need for survival and reproduction. Food, water, shelter, avoiding predators, and finding mates all involve interactions with an objective reality external to an animal’s neurophysiology.
Since survival and reproduction depend on our interaction with matter and energy that exists beyond our neurology, it is safe to conclude that our neurology has evolved in such a way that it provides an accurate representation of this exterior reality. Furthermore, since the truthfulness of our beliefs can only be evaluated in terms of comparing it to our external environment, what other process of development would produce a more reliable method of picturing true reality than an evolutionary process that directly interacts with this external reality (think photons on retinal G-protein coupled receptors, or olfactory sensory neurons)? These neurological functions directly provide information about the universe beyond our physical body. Since the external reality that stimulates our neurology, and the external reality to which we compare beliefs to evaluate their truthfulness are the same, we can reasonably conclude that our neurology is generally reliable, albeit imperfect, in producing beliefs about this reality (at the very least, better than 50/50 as Plantinga claims).
The confusion created by Plantinga relies on the assertion of a proposition without subsequently testing that proposition for its truth value. Humans constantly evaluate their beliefs in terms of the evidence supporting them (i.e., is it safe to cross the street, is the pan hot, is this food spoiled, etc?). In Plantinga’s example of frogs eating flies, he states that they could eat flies because flies are good to eat (true belief—defined by Plantinga), or because the right fly might turn them into a prince (adaptive/false belief). Now, according to Plantinga both of these situations have an equal likelihood of occurring in the context of evolutionary naturalism. Even if that were true, humans still have the capability of evaluating and testing beliefs so that our degree of certainty of their truth is appropriate for the amount of evidence to support it. Therefore, even if belief propositions had an a priori truth probability of 1:1, empirical evidence could still allow us to rationally hold belief sets by refining a posteriori truth probabilities. Such evidence can be created by controlled, scientific experiments in which researchers test a single variable while making only the minimum number of assumptions necessary to conduct the inquiry.
Does Plantinga think our neurology is reliable? From Plantinga’s statement that “if God created man in his image then God would create us in such a way that we could know things,” we can assume that he thinks our neurology is reliable. It is troubling to note, however, that Plantinga’s examples all deal with individual impressions. Are we to assume that Plantinga feels individual impressions are reliable and to be trusted? This view would be completely antithetical to the position of modern science. In science, we assume that even though our neurology is useful and able to experience an external reality, individual impressions are inherently unreliable. Therefore, our certainty should be based on repeatable, testable, and falsifiable experiments. Plantinga, on the other hand, says that individual impressions are reliable because they are held by people made in the image of God. His view is not surprising since many religious phenomena rely very heavily on individual impressions (miracles, relationships with God, emotional significance of religious ceremonies, answered prayers, etc). Would Plantinga really want to see a world in which his view on the reliability of individual beliefs is universally accepted? I doubt it.
The important point is that we can arrange our certainty to be commensurate with the amount of supporting experimental evidence. The relationship between truth-certainty and available evidence is what allows us to hold rational beliefs in spite of an imperfect neurology and individual impressions. The rationality of beliefs, then, depends on the testability and falsifiability of propositions. In other words, given an evolved neurology which can confuse coincidence with cause and effect, we can make progress towards truth only if the propositions are testable and falsifiable. Otherwise, we cannot create evidence at all (untestable) or we face an infinitely expanding tautology (unfalsifiable). Plantinga’s answer to the problem of an imperfect neurology is not a method of evaluating the truthfulness of neurologically based propositions. Instead, Plantinga only succeeds in introducing an untestable and unfalsifiable alternative. Such an introduction does not offer progress towards truth. Instead, it precludes further progress towards truth by creating an unnecessary and immovable obstacle when we already have tools for truth-seeking at our disposal.
We have seen that the reliability of neurology is dependent on the process of evolution. If this process is naturalistic, or if a God exists, the process still relies on direct interaction between the neurology of the organism harboring the genetic material and the external environment. The dynamic relationship between environment and organism, as well as this relationship’s role in adaptive fitness of the organism, suggests that our neurology exists in such a way that it accurately represents the reality exterior to it. Additionally, insofar as our neurology is capable of holding false beliefs, it is also capable of creating and understanding empirical methods to evaluate the truthfulness of beliefs manifested by our neurology. However, since those beliefs are a conscious manifestation of neurology that accurately experiences reality, and truth is defined by comparisons to the same reality, we can reasonably conclude that beliefs, while far from perfect, are better than Plantinga’s 50/50 suggestion.
Most importantly, acknowledging an imperfect neurology does not preclude an individual from rationally believing both naturalism and evolution. As with all propositions, if an individual can design a way to test that proposition and offer a falsifiable condition prior to testing, evidence can be created to determine truthfulness. It is the arrangement of our certainty of truth in accordance with such evidence that has served to support the theory of evolution. If an individual were to hold a belief, test it hundreds of times, always achieve the falsifiable condition, and then continue to hold the belief, then that belief is irrationally held. On the other hand, if the falsifiable condition is never met, then the person can reasonably hold the belief as being true. Such is the case with evolution. All of the available evidence, converging from paleontology, molecular genetics, comparative anatomy, cosmology, biogeography, etc., indicates that evolution is true. So, regardless of any original individual impressions of adaptive neurology, the only rational position is to accept evolution.