What is Plantinga's "Evolutionary Argument Against Naturalism" (EAAN), and does it succeed in proving that naturalism undermines itself?

The Evolutionary Argument Against Naturalism (EAAN) is among the strangest and cleverest arguments in contemporary philosophy of religion. Alvin Plantinga formulated it in the 1980s and developed it in his book "Warrant and Proper Function" (1993). The argument does not attack biological evolution, but rather attempts to prove that combining naturalism and evolution leads to epistemological self-undermining. Understanding the argument's intricacies is necessary for fair evaluation.

Inadequate Responses to Avoid

From some defenders of theism:

"Plantinga destroyed atheism with this argument." An unjustified exaggeration. The argument is highly technical and depends on precise assumptions about probabilities and epistemic reliability. Even if successful, it does not "destroy" atheism, but rather poses an epistemological problem for a certain formulation of naturalism. Many atheist philosophers (such as Elliott Sober and Paul Draper) have offered serious technical responses.

"The argument proves evolution is false." A complete misunderstanding. Plantinga himself accepts biological evolution as a correct scientific theory. His argument targets "naturalism + evolution" together, not evolution alone. Conflating the two weakens the argument and turns it into something its author never intended.

From some naturalists:

"The argument is merely a logical game unrelated to science." A misleading simplification. The argument draws on concepts from evolutionary psychology, epistemology, and philosophy of mind. Dismissing it as a "logical game" ignores its philosophical depth and connection to serious discussions in philosophy of biology.

"Evolution ensures the correctness of our beliefs because false beliefs are harmful to survival." This is precisely what the argument challenges. Plantinga distinguishes between adaptive behavior and correct beliefs, arguing that evolution selects for useful behavior, not necessarily correct beliefs. This simple response assumes what the argument attempts to refute.

Why These Responses Are Inadequate

Responses from both sides share a failure to engage with the argument's technical structure. The argument relies on precise analysis of the relationship between beliefs, behavior, and natural selection. Evaluating it requires understanding these relationships carefully, not mere general slogans.

Structure of the Evolutionary Argument Against Naturalism

Plantinga begins by defining philosophical naturalism: there is no God or anything like God, and humans are the product of blind, unguided evolutionary processes. He then poses the central question: in such a world, what is the probability that our cognitive faculties are reliable (i.e., produce mostly true beliefs)?

First Step: Distinguishing Between Beliefs and Behavior

Evolution selects for adaptive behavior (which aids survival and reproduction), not directly for true beliefs. The question is: does adaptive behavior require true beliefs? Plantinga argues: not necessarily.

Illustrative example: imagine a primitive creature seeing a tiger. Four possibilities for the relationship between its beliefs and behavior:
1. True belief + normal desire = believes it's a dangerous tiger + wants to survive ← flees
2. False belief + strange desire = believes it's a friendly deity + wants to distance himself from deities out of respect ← flees
3. Another false belief + stranger desire = believes running makes him happy + wants happiness ← flees
4. No conscious beliefs, merely neural mechanisms causing automatic flight

In all cases, the behavior is adaptive (fleeing the tiger). But in three of four cases, beliefs are either false or absent. Natural selection "sees" only behavior, not beliefs.

Second Step: Calculating Probabilities

Plantinga symbolizes: P(R|N&E) = probability that our cognitive faculties are reliable (R) given naturalism (N) and evolution (E).

His argument: this probability is low or indeterminate. Why? Because evolution in a naturalistic world selects for adaptive behavior, and adaptive behavior does not require true beliefs. Therefore, there is no strong reason to expect our cognitive faculties to be reliable.

Third Step: Self-Defeat

If P(R|N&E) is low, then the evolutionary naturalist has a "defeater" for all his beliefs, including his belief in naturalism and evolution themselves. It's like someone discovering he took a drug that causes hallucinations in 90% of cases—he must doubt all his current beliefs, including his belief that he took the drug!

This is what Plantinga calls "self-defeat": evolutionary naturalism undermines confidence in human reason, but confidence in human reason is required to justify evolutionary naturalism itself. An epistemological vicious circle.

Serious Responses from Naturalists

The Causal Connection Objection (Jerry Fodor). In practice, beliefs and desires are systematically causally connected. The belief "tiger is dangerous" typically causes fleeing behavior. Evolution selects for these interconnected systems, not isolated behavior.

Plantinga's reply: This assumes that "correct" causal connection between beliefs and behavior is evolutionarily favored. But why? "Incorrect" connection systems might be equally adaptive.

The Simplicity Objection (Elliott Sober). Simple, direct cognitive systems (true beliefs ← appropriate behavior) are more evolutionarily likely than complex systems (false beliefs + strange desires ← appropriate behavior).

Plantinga's reply: This assumes evolution "prefers" simplicity. But evolution favors only adaptive efficiency. If a complex system works, there's no selective pressure toward simplicity.

The Narrow Content Objection (Ruth Millikan). Evolution selects for the narrow content of mental states (how they represent the world internally), not just external behavior. Accurate representations of the world are adaptively useful.

Plantinga's reply: Even if evolution selected for representations, the question remains: are "useful" representations necessarily "correct"? Simplified or distorted representations might be more useful for survival.

Critical Evaluation: Strengths and Weaknesses

Strengths:
- Highlights a genuine tension between naturalism and the reliability of human knowledge
- Uses naturalists' own tools (evolution) against them
- Raises deep questions about the relationship between evolution and truth

Weaknesses:
- Relies on possible but improbable scenarios (systematically false beliefs)
- Ignores evidence from cognitive psychology on the tight connection between accurate perception and survival
- The conclusion (naturalism is false) is stronger than the premises

A Middle Position: Epistemological Challenge Without Metaphysical Resolution

Perhaps the most balanced position is to acknowledge that Plantinga poses a serious epistemological challenge to naturalism, without saying he "refutes" it definitively. The argument shows that the naturalist needs an additional explanation for why we trust our cognitive abilities—an explanation that doesn't come free from evolution alone.

On the other hand, the naturalist can respond that evolution, while not "guaranteeing" truth, makes it probable enough for practical confidence. The gap between "probable" and "guaranteed" may not be epistemologically fatal.

Where We Stand in This Debate Today

The debate remains active. Developments in evolutionary psychology and neuroscience provide new data about the relationship between beliefs and behavior. Meanwhile, philosophers of mind are developing more sophisticated theories of mental content and representation.

The argument remains an important contribution in showing that naturalism is not a simple "default" position, but carries deep philosophical commitments requiring defense. This aligns with the rational weighing approach (rajḥān ʿaqlī): no final resolution, but continuous balancing of arguments.