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The Empirical Case for Metaphysical Naturalism

Anyone who has followed the creationist movement for the last 10 years or so has probably encountered a new argument in the arsenal of creationists. I call it “the argument from bias.” The claim is that evolutionists are so biased that they a priori rule out the mere possibility of the supernatural. For example, anti-evolutionist Phillip Johnson writes,

To Darwinists, evolution means naturalistic evolution, because they insist that science must assume the cosmos to be a closed system of material causes and effects that can never be influenced by anything outside of material nature–by God, for example.1

Johnson argues that because evolutionists are committed to naturalism, they ignore evidence which might suggest creationism or which might cast doubt on evolution. He writes, “To Darwinists the ability to imagine the process is sufficient to confirm that something like that must have happened.”2

Several individuals — naturalists and anti-naturalists alike — have pointed out the errors in Johnson’s claims. Creationist Owen Gingerich, writing in Perspectives on Science and Christian Faith, notes that Johnson defines evolution as inherently naturalistic philosophy, despite the fact that the majority of evolutionists are not naturalists.3 Eugenie Scott, executive director of the National Center for Science Education, states that science is methodologically naturalistic; science “explains the natural world using only natural causes.” As Scott points out, this does not mean that science presupposes metaphysical naturalism, the belief that there are no supernatural beings.4 And Terry Gray, a self-described creationist at Calvin College, has criticized Johnson’s attacks on the scientific evidence for evolution. He writes, “It is not clear to me what kind of evidence [for evolution] Johnson would find persuasive.”5

I agree with all of these points. However, there is an additional reason why I reject the claim that “evolutionists a priori rule out the evidence for the supernatural.” My reason is this: there are good empirical reasons for believing that metaphysical naturalism is true, and therefore a denial of the supernatural need not be based upon an a priori assumption.

Some Evidence for Metaphysical Naturalism

Here I want to give two lines of empirical evidence which I think support metaphysical naturalism. Although I believe there are additional facts which support naturalism, space limitations require that I limit myself to just two lines of evidence. I shall attempt to argue that these two facts are much more likely on naturalism than theism.

(1) Naturalism makes sense of the physical nature of minds.

As Paul Draper, an agnostic philosopher at Florida International University, puts it, “Consciousness and personality are highly dependent on the brain. Nothing mental happens without something physical happening.”6 Now Michael Tooley, a philosopher at the University of Colorado at Boulder, has stated five lines of evidence in support of this claim. Let me summarize just briefly that evidence. First, when an individuals brain is directly stimulated and put into a certain physical state, this causes the person to have a corresponding experience. Second, certain injuries to the brain make it impossible for a person to have any mental states at all. Third, other injuries to the brain destroy various mental capacities. Which capacity is destroyed is tied directly to the particular region of the brain that was damaged. Fourth, when we examine the mental capacities of animals, they become more complex as their brains become more complex. And fifth, within any given species, the development of mental capacities is correlated with the development of neurons in the brain.7 Thus, the conclusion that, “Nothing mental happens without something physical happening,” seems inescapable.

But if nothing mental happens without something physical happening, that strongly implies that the mind cannot exist independently of physical arrangements of matter. In other words, we do not have a soul. And this is exactly what we would expect if naturalism is true. But if theism is true, then our minds should not depend on our brains for their existence; we should have souls. Also, if theism is true, then God is a disembodied mind; Gods mind is not in any sense dependent on physical arrangements of matter. But if nothing mental happens without something physical happening, that is evidence against both the existence of souls and the existence of any being who is supposed to have a disembodied mind, including God. Therefore, the physical nature of minds is unlikely if theism is true, but what we would expect if naturalism is true.

(2) Naturalism makes sense of the pointless evil and suffering in the world.

Have you ever wondered why there is so much evil and suffering in the world? In addition to evils committed by human beings, there is much agony and pain caused by solely natural processes, including earthquakes, tornadoes, floods, and viruses. Recently, a new type of virus has evolved that makes AIDS seem like a common cold. Biochemists call these viruses “hot viruses,” and I want to read you a short, graphic description of what happens to someone infected with a hot virus. Brace yourself. After becoming infected with a hot virus, the victim

becomes dizzy and utterly weak, and his spine goes limp and nerveless and he loses all sense of balance. The room is turning around and around. He is going into shock. He leans over, head on his knees, and brings up an incredible quantity of blood from his stomach and spills it onto the floor with a grasping groan. He loses consciousness and pitches forward onto the floor…. Then comes a sound like a bedsheet being torn in half… He has sloughed his gut…. [The victim] has crashed and is bleeding out…. Having destroyed its host, the hot agent is now coming out of every orifice, and is “trying” to find a new host.8

Now, this tends to be pretty embarrassing for the theist. If theism is true, we have to believe that God allows people to suffer horrible pain that any decent person would themselves prevent. But that’s hard to believe. If there is a God, He is more than just a decent person; He is the very standard of decency itself. So why doesn’t he just eliminate evils like the one I just described? Even after thousands of years of theological reflection, theistic philosophers still have no idea. They just assume that there must be a reason for God allowing evil. For example, Alvin Plantinga of Notre Dame University, one of the most influential theistic philosophers of our time, admitted, “Many of the attempts to explain why God permits evil … seem to me shallow, tepid, and ultimately frivolous.”9 Naturalists, on the other hand, have a plausible explanation for pointless suffering: there is no all-good, all-powerful, all-knowing being to intervene and prevent pointless suffering. Therefore, pointless suffering is much more likely on naturalism than on theism.


Thus, I think the metaphysical naturalist is amply justified in concluding that the universe is a closed system, and I therefore strongly disagree with Johnson’s portrayal of metaphysical naturalism as an arbitrary, a priori assumption. It follows that even if evolution were based on metaphysical naturalism (which it is not), that dependency would be a strength, not a weakness. Metaphysical naturalism may be a philosophical belief, but it is a belief supported by empirical evidence.


1 Phillip Johnson, Darwin on Trial (Regnery, 1991), pp. 179-180.
2 Ibid., p. 180.
3 Owen Gingerich, “Further Reflections on ‘Darwin on Trial’,” Perspectives on Science and Christian Faith, Vol 44 No 4, December 1992, pp. 253-254 quoted in Jim Lippard and Bill Hamilton, “Critiques of Anti-Evolutionist Phillip Johnson’s Views” (<URL:http://www.talkorigins.org/faqs/johnson.html, 1994), spotted 1 Feb 99.
4 Eugenie Scott, “Darwin on Trial: A Review” (<URL:http://www.natcenscied.org/aladont.htm>, n.d.), spotted 1 Feb 99.
5 Terry M. Gray, “The Mistrial of Evolution” (<URL:http://mcgraytx.calvin.edu/gray/evolution_trial/dotreview.html>, 1992), spotted 1 Feb 99.
6 Paul Draper, “Opening Statement” in William Lane Craig and Paul Draper, Does God Exist? (videotape, West Point, NY, 1996).
7 Michael Tooley, “Opening Statement” in William Lane Craig and Michael Tooley, Does God Exist? (<URL:http://www.leaderu.com/offices/billcraig/docs/craig-tooley2.html>, 1994), spotted 1 Feb 99.
8 Richard Preston, The Hot Zone (New York: Anchor, 1994), pp. 23-24.
9 Alvin Plantinga, “Epistemic Probability and Evil” in The Evidential Argument from Evil (ed. Daniel Howard-Snyder, Indianapolis: Indiana University Press, 1996), p. 70.