Evolutionary Argument Against Naturalism

Overview and Background

The Evolutionary Argument Against Naturalism (EAAN) is a contemporary philosophical argument, most fully developed by the analytic philosopher Alvin Plantinga. It aims to show that a person who accepts both naturalism (the view that there is no God or anything like God, and that the natural world is all there is) and unguided evolutionary theory has a reason to doubt the reliability of human cognitive faculties. If those faculties are unreliable, then all beliefs formed by them—including the belief in naturalism and evolution—are undermined.

Rather than objecting to evolution itself, the EAAN targets the combination of evolution with metaphysical naturalism. It is primarily an epistemological argument (about the justification of belief), not a direct argument for the falsity of evolution or for the truth of theism. Proponents present it as a self-defeat or internal inconsistency challenge to naturalistic worldviews.

Core Structure of the Argument

Plantinga’s formulation proceeds by connecting evolutionary biology with theories of content, belief, and rationality.

1. Naturalistic evolution and selection for survival

Under naturalistic evolution, cognitive faculties (such as perception, memory, and reasoning) are shaped by natural selection. Selection operates on behavioural traits and underlying neural structures in ways that enhance survival and reproductive success. Proponents of EAAN emphasize that fitness does not automatically track truth: what matters for evolution is that behaviour is adaptive, not that beliefs are accurate.

Plantinga illustrates this with thought experiments in which an organism survives with wildly false beliefs, so long as those beliefs consistently produce adaptive behaviour. For example, an early human might have the false belief that tigers are friendly but that the best way to “hug” them is to run away; the behaviour (running away) is adaptive, even though the belief content is false.

2. Probability of reliable cognition on N&E

The key probabilistic claim concerns P(R | N & E)—the probability that our cognitive faculties are reliable (R) given naturalism (N) and evolution (E). Reliability here is understood as producing a high proportion of true beliefs in the relevant environments.

Plantinga argues that P(R | N & E) is either low or at best inscrutable (we lack any good reason to regard it as high). Because selection tracks behaviour, not truth as such, there is no clear reason—on a purely naturalistic evolutionary picture—to expect cognitive systems that form mostly true beliefs rather than systematically false-but-adaptive ones. If reliability is improbable or unknown, then, by the laws of probability and epistemic norms, a naturalist-evolutionist acquires a defeater for trusting their own cognitive faculties.

3. Self-defeat and global skepticism

If one has a defeater for the reliability of one’s cognitive faculties, then one has a defeater for all the products of those faculties. This includes:

• ordinary empirical beliefs,
• scientific theories (including evolutionary theory),
• and crucially, naturalism itself.

Thus, the conjunction N & E appears self-defeating: if one accepts it, one has a reason to doubt every belief produced by evolved cognition, and therefore a reason to doubt N & E itself. Proponents conclude that naturalism, when combined with evolution, leads to an unstable position verging on global skepticism.

Major Objections and Replies

Philosophers have widely debated the EAAN. Criticisms target its assumptions about evolution, rationality, content, and probability.

1. Adaptive success and truth-tracking

A central objection is that true beliefs are, in general, adaptively advantageous, so P(R | N & E) may in fact be high. If an organism’s beliefs about predators, food sources, and physical obstacles are largely false, its behaviour is likely to be maladaptive. Critics argue that:

• While isolated false beliefs can aid survival, systematically unreliable cognition would typically decrease fitness.
• Therefore, selection tends to favor approximately veridical (truth-tracking) cognitive systems, at least in ordinary environments.

Proponents of EAAN reply that evolution can favor reliable behaviour without requiring true belief content; beliefs could be largely epiphenomenal or systematically misaligned with the world, as long as the underlying cognitive mechanisms produce adaptive actions.

2. Content externalism and causal constraints

Some critics appeal to content externalism and naturalistic theories of mental representation: what makes a state a belief about, say, water rather than something else, is partly its causal relation to water in the environment. On such views, beliefs formed by faculties successfully interacting with the world are unlikely to be massively false. There are, they argue, strong natural constraints making global error improbable.

Plantinga responds that these semantic theories do not automatically ensure a high degree of truth across the whole belief system, particularly in abstract domains (science, metaphysics, ethics) that go beyond local causal interactions.

3. Local vs. global skepticism

Another objection maintains that EAAN proves too much: if its reasoning is correct, it undercuts any theory that allows for the possibility of cognitive error, including theistic evolution or even theism. Critics contend that the argument resembles familiar skeptical scenarios (e.g., brain-in-a-vat hypotheses) and thus does not uniquely threaten naturalism.

Supporters argue that EAAN differs by being an internal critique: it uses premises that naturalists often accept (about unguided evolution and physicalist accounts of mind) to reach a skeptical conclusion specifically about N & E, while theists can posit a truth-aimed designer of cognitive faculties.

4. The “conditionalization” and coherence objection

Some philosophers suggest that once we conditionalize on the fact that science and everyday reasoning are highly successful (e.g., technologies work, predictions are confirmed), we have strong empirical evidence that our faculties are reliable. Thus P(R | N & E & our success data) may be high, and the EAAN’s focus on P(R | N & E) alone is incomplete.

Defenders reply that the very use of such empirical success as evidence already presupposes trust in our cognitive faculties. If those faculties are under a probabilistic cloud given N & E, then they argue that appealing to their outputs to boost P(R) is epistemically circular.

Philosophical Significance

The Evolutionary Argument Against Naturalism occupies an important place at the intersection of philosophy of religion, epistemology, and philosophy of mind.

• In the philosophy of religion, it functions as an indirect argument that naturalism is epistemically unstable, sometimes framed as a “reformed” alternative to traditional theistic proofs. It does not purport to prove theism, but to weaken a rival worldview.
• In epistemology, the EAAN raises questions about the conditions under which we can trust our cognitive faculties, the nature of defeaters, and the extent to which evolutionary explanations can be epistemically benign or corrosive.
• In the philosophy of mind, it presses naturalists to articulate how truth-tracking mental content arises from physical systems shaped by selection, and whether reliable reasoning is to be expected in a purely physical, unguided evolutionary history.

The argument remains highly controversial. Some see it as a powerful internal challenge to naturalistic worldviews; others regard it as relying on mistaken assumptions about evolution, content, or probability, or as failing to show any special problem for naturalism beyond familiar general skepticism. Its ongoing discussion continues to refine debates about the relationship between evolution, naturalism, and rational belief.