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What's in a Word? "Randomness" in Darwinism and the Scientific Theory of Evolution

random dice.jpg

This is the third in a series of reviews of Alvin Plantinga's important new book, Where the Conflict Really Lies. For parts one and two, see here and here. For Plantinga's reply, see here.

One of the more difficult parts of Plantinga's book is his discussion of "randomness" in Darwinian evolution, and the related questions of "Darwinism" and the "scientific theory of evolution." In fact, the discussion is easily misinterpreted and potentially confusing, so let's consider it at length.

Plantinga offers several important clarifications on these subjects. Unlike so many who occupy the overlapping space of science and religion, he recognizes that the word "evolution" can refer to many things, and he's careful not to hide his own views in the ambiguity. "Evolution" can refer simply to change over time, or to the idea that the universe and earth are billions of years old. It can refer to the common ancestry of life. It can even refer, confusingly, to the chemical origin of life, which wasn't part of Darwin's theory. It can also refer to common descent, the idea that all living things are descended from one or a few common ancestors. And it can refer to that idea plus a mechanism for change. In the case of Darwinism, the mechanism is natural selection sifting the random variations in reproducing populations -- or what Darwin often called "chance" variations. In the modern form of the theory -- Neo-Darwinism -- new variations are identified with mutations in DNA.

Plantinga argues, plausibly, that most of these senses of "evolution" present no logical challenge to Christian theism. In Darwinism, however, many perceive a conflict. Isn't the whole point of the theory to provide a process or mechanism that can overcome the prohibitive barriers of mere chance and can mimic the work of an intelligent agent? When most biologists claim that adaptive complexity is largely the result of natural selection and random genetic mutations, don't they intend to provide an alternative to design? Don't they claim that selection and mutation, considered together as a single process, are unguided?

Despite appearances to the contrary, Plantinga thinks these questions are based on misunderstanding. He sees denial of purpose not as a part of Darwinism or the scientific theory of evolution, but as merely a metaphysical or philosophical add-on. There's "Darwinism," and then there's "unguided Darwinism." In his view, the scientific theory, which we can call Darwinism, affirms natural selection and random genetic mutations as the engine of adaptation, but makes no claims about purpose or the lack thereof in the history of life.

Getting the Main Issue Right

The word "random" (and its near synonym "chance") is a notorious source of mischief in science and religion discussions, so it's important to follow Plantinga's argument closely. Leaving terminological difficulties to the side for a moment, Plantinga must be commended for getting to the heart of the question over the compatibility of theism and evolutionary theory and for coming down on the right side: namely, purpose or guidance. Christian theism is committed to the idea that God intends certain things to come out a certain way in history. He intended human beings, for instance. He knew you before he knit you together in your mother's womb. So theism will be incompatible with any view, including any evolutionary theory, that denies that life and its history were purposively guided to accomplish God's ends.

On this, the central question, Plantinga gets it exactly right. Contrary to some contemporary theistic evolutionists, he understands that an event can't be both guided and unguided, both purposeful and purposeless. Far too many discussions of "God and evolution" appeal to God's mystery or his transcendence or his majesty or the fact that he's "not a Cosmic Tinkerer," to disguise a contradiction. Plantinga doesn't talk about "horizontal" versus "vertical" causality (as physicist Stephen Barr does). He doesn't cite St. Thomas' references to "contingency" and "chance," which had different meanings for Thomas than they have in the modern Darwinian context. And he doesn't make reconciliation easy by just stipulating a teleological definition of "random." He does discuss the possibility that an event might appear unguided to us but still be guided by God. There's no contradiction in that case because the event isn't really unguided. Looking unguided and being unguided are two different properties.

At the same time, he wants to show that there's nothing in theistic religion that conflicts with "science." This goal is nowhere more difficult than when he deals with the reigning theory of biological evolution, depending as it does on the Darwinian process of natural selection and "random" mutations. As a result, Plantinga must find a "scientifically reputable" definition (my phrase) of the word "random." This will be a definition that doesn't assume that the history of life either has or has not been guided. Natural science, we're told, is supposed to be empirical and not beg big metaphysical questions. If that's true, then we need a sense of the word that is metaphysically neutral. Plantinga finds just such definitions offered by Ernst Mayr and philosopher of biology Elliott Sober.

"When it is said that mutation or variation is random," Mayr explains, "the statement simply means that there is no correlation between the production of new genotypes and the adaptational need of an organism in a given environment."1 Sober defines "random" even more carefully: "There is no physical mechanism (either inside organisms or outside of them) that detects which mutations would be beneficial and causes those mutations to occur."2 Mutations' "being random in that sense," Plantinga notes, "is clearly compatible with their being caused by God" (p. 13).

Certainly, given theism, it's logically possible that an event such as a genetic mutation could be guided directly by God and independently of any physical mechanism. As a result, Plantinga can say that the Christian view "that God intended to create creatures of a certain kind" is "consistent with Darwinism, the view that the diversity of life has come to be by way of natural selection winnowing random genetic mutations" (p. 11). Note that he's defined Darwinism using Sober's, um, sober definition of "random."

Plantinga's logical point stands. Unfortunately, practically no one restricts the meaning of the word "random" in this way, and, a fortiori, few if any see Darwinism as limited to such a narrow definition. There are really three related terms at issue here: "random," "Darwinism," and the "scientific theory of evolution." In fact, even if all Darwinists adhered to Sober's precise definition, most would assume that Sober is offering a distinction without a difference, since physical mechanisms are the only mechanisms that exist.

Plantinga recognizes that it's "not entirely easy to say" what "contemporary evolutionary science claims" (p. 15). And yet in describing Darwinism he says: "If these mutations are random, aren't they just a matter of chance? But randomness, as construed by contemporary biologists, doesn't have that implication." This implies that contemporary biologists do have some unanimous sense of "random" to which they adhere, and that there is an official definition of the theory. But Plantinga has merely given two very narrow definitions of the word "random" in evolutionary theory by one scientist and one philosopher; he hasn't shown that these definitions are representative.

For Darwin and most Darwinists, in fact, random doesn't just mean uncorrelated to a physical mechanism that works in favor of organisms. Random mutations have some or another cause, to be sure, but the cause, in the Darwinian view, is blind, unguided, and purposeless. Unlike the meter, for example, which is officially defined as the length of the path travelled by light in vacuum in 1⁄299,792,458 of a second, there is no standard definition of Darwinian Theory. So we are left with the intentions of Darwin and those who follow him, and, to some extent, the ordinary meanings of the words they use.

What the Dictionary Says

And given ordinary English usage, Darwinists are quite right to use the word in that sense. Here's how Merriam Webster defines the adjectival form of the word:

1 a : lacking a definite plan, purpose, or pattern
Even the statistical meaning of the word in Merriam Webster has to do, not just with a lack of correlation, but with having an equal probability of success:
2   a : relating to, having, or being elements or events with definite probability of occurrence ‹random processes›

  b : being or relating to a set or to an element of a set each of whose elements has equal probability of occurrence ‹a random sample›; also : characterized by procedures designed to obtain such sets or elements ‹random sampling›

When used as a noun, Webster's gives fewer options:
: a haphazard course
  -- at random
: without definite aim, direction, rule, or method ‹subjects chosen at random
I checked five other English dictionaries. They say more or less the same thing. It's no wonder, then, that when Darwinists use the word "random," they mean, and are rightly understood to mean, purposeless and unguided, even when they don't use those additional adjectives. This is not the result of confusion. It's the result of Darwinists using the standard meaning of the word. Besides, it's their theory, so they have the privilege of defining it however they see fit. Our task is to evaluate it based on reason and evidence.

You don't evaluate an argument of philosophical significance by citing the dictionary, of course. My point is to make it clear that using the word "random" in a highly circumscribed, metaphysically neutral way and then importing that to "Darwinism" is largely a private game. Clearly neither Darwin nor his followers have chosen to play the game by the same rules.

Darwinists Normally Intend to Offer an Alternative to Real Teleology

Even when they do not explicitly deny the possibility of purpose and design, Darwinists intend to make teleological explanations in biology superfluous. Darwin, unlike some earlier materialists who were content to appeal to blind chance, wanted to accommodate the appearance of purpose and teleology in the biological world. "Chance" determines which variations arise (to speak commonly though somewhat paradoxically), but not which variations are selected and perpetuated. This has led some scholars to describe Darwin's theory as itself teleological.3 But this is sloppy speaking, since it blurs the whole point of Darwin's proposal. He sought to provide an explanation for the appearance of purpose, but without recourse to real purpose.

Darwinists have followed in this tradition. They claim that random mutations are sifted by natural selection, and this blind and purposeless process as a whole gives rise to things that look designed, but aren't. They don't mean that natural selection and random variation are just a small part of the story. They intend for the Darwinian mechanism to provide a more or less sufficient causal explanation of the feature in question, though they often include other secondary physical factors alongside natural selection. The total set of blind physical causes is intended to provide the complete explanation of the feature. And that intention is incompatible with God guiding the mutations.

Now that I think of it, even Sober's highly restrained definition of "random" needs to be filled out to make selection-and-mutation clearly compatible with purposeful guidance and to rule out the a-teleological intentions of Darwinian theorists. The process needs to be defined in something like the following way:

When we say that an adaptation is the result of natural selection and "random" genetic mutations, we mean: (1) There is no physical mechanism (either inside organisms or outside of them) that detects which mutations would be beneficial and causes those mutations to occur, and (2) there is no implication that natural selection and random mutation are complete or causally adequate explanations of adaptive complexity. (3) There is no implication that other, non-physical causes are not also required to explain adaptations and other, empirically manifest features of organisms.
Now we have a definition of Darwin's mechanism that is unambiguously compatible not just with intelligent design, but with Christian theism. We also have a definition that no one has ever used, until now.

A Denial of Real Teleology is the Essence of Darwinism

Plantinga says that "if we think of the Darwinian picture as including the idea that the process of evolution is unguided, then of course that picture is completely at odds with providentialist religion [which holds that everything that happens is intended or permitted by God]. As we've seen, however, current evolutionary science doesn't include the thought that evolution is unguided; it quite properly refrains from commenting on the metaphysical or theological issue" (p. 55). And then he defines "Darwinism" in such a way that it does not "seem to cut against providentialist religion" (p. 55).

This is a perplexing claim, especially since Plantinga cites in a footnote on the previous page Casey Luskin's article in God and Evolution. Luskin demonstrates that leading biology textbooks over and over and over and over again explain biological evolution in just the way Plantinga claims "current evolutionary science" does not. In fact, as the editor of God and Evolution, I asked Luskin to remove many of the examples he provided in the first draft of his chapter. He had provided far more examples than were necessary to prove the point. Do all these leading biology textbooks fail to teach "current evolutionary science"? Not likely. Thomas Kuhn rightly referred to textbooks as "pedagogical vehicles for the perpetuation of normal science." Normal science, for Kuhn, doesn't involve cutting edge discoveries that threaten to overturn the reigning scientific paradigm, but is rather the paradigm itself.

The denial of design and teleology in biology is an essential part of Darwinism and, unfortunately, it is how the modern theory of biological evolution is taught, explained, and understood by the vast majority of its champions and critics.

Of course, there were some who tried early on to reconcile Darwin's theory with teleology, but they mistook Darwin's intention in doing so. Asa Gray is the most prominent example. He sought to reconcile Darwin's theory with natural theology, and urged Darwin to allow that God oversaw which variations would occur and when. Darwin famously rebuked -- even mocked -- Gray for making this suggestion, which Darwin insisted was no part of his theory.4

Similarly, Alfred Russel Wallace, co-discoverer of natural selection who later broke with Darwin, wrote a book entitled Darwinism in 1889. He continued to consider himself a "Darwinist" even after he rejected Darwin's materialistic applications to man, sentience, and the origin of life. He had a personal relationship with Darwin and so was more inclined to criticize Darwin's surrogates, such as Haeckel and Huxley -- a tradition that continues to the present. When Herbert Spencer received his complimentary copy of Darwinism, however, he wrote to Wallace, "I regret that you have used the title 'Darwinism,' for notwithstanding your qualification of its meaning you will, by using it, tend greatly to confirm the erroneous conception almost universally current."5 The erroneous conception was that Darwinism and Wallace's teleological or intelligent evolution were compatible. Spencer understood that they were not.

In his famous article "Darwin's Influence on Modern Thought" in Scientific American (July 2000), Ernst Mayr dropped the modest pretense we saw above in his definition of "random," and explained that Darwinism offers "a secular view of life." Here are a couple of his salient points:

Darwinism rejects all supernatural phenomena and causations. The theory of evolution by natural selection explains the adaptedness and diversity of the world solely materialistically. It no longer requires God as creator or designer (although one is certainly still free to believe in God even if one accepts evolution).

Darwin's theory of natural selection made any invocation of teleology unnecessary.

Darwinism rejects all supernatural phenomena and causations. Since Mayr was one of the preeminent leaders of the Darwinian tribe in the twentieth century, I'm inclined to trust that he knows what Darwinism is. Notice his concession, characteristic of all but the most fanatical Darwinists, that one can believe in God and evolution. But he's not talking about evolution that is really and apparently guided by God. He's saying that you're free to believe in a God back there behind the scenes not acting in any tangible way or explaining anything we find in the world.

I'll resist the temptation to offer similar quotes from Darwin's notebooks, which make it clear how deeply materialistic (and not just deistic) his views were, and from leading Darwinists and official scientific organizations, who confirm what we've already seen.6

Take the Flagellum, For Example

Darwinism is the attempt to substitute a blind, material process for real teleology. Take the debate over the famous bacterial flagellum. Darwinists assume that given the time available, unguided natural selection and mutations can produce it, perhaps by way of several functional precursors. They've spent the last fifteen years since Mike Behe wrote Darwin's Black Box trying to come up with such scenarios to explain it in this way. Now let's say that researchers spend years finding the pathway by which this would need to happen, and they determine that getting a working flagellum from some flagellum-free species of bacteria requires 153 independent mutations to happen simultaneously. None of them individually and no subset provides the bacterium a survival advantage, so an unguided Darwinian process, which lacks the foresight to select that functional flagellum and take the steps necessary to attain it, would almost certainly never accomplish the goal.

However, (assuming theism) God could act directly, rather than through an additional physical process, to make sure these mutations take place when they need to, namely, simultaneously. Let's say that is what happened. So the best, correct and complete causal explanation for the origin of the flagellum would be that God directly guided 153 mutations (without using another physical mechanism) so that the bacteria would enjoy functioning flagella. This wouldn't just be intelligent design, but divine design. And given the tightly specified complexity of a flagellum -- the function in this case is the specification -- it would be empirically detectible, even obvious, design: real design, real teleology, not an unguided Darwinian process.

The alternative to intelligent design would be an unimaginably improbable run of chance. Now, would any Darwinist think this is a perfectly acceptable outcome for his theory? Chance here is no explanation at all, yet surely no Darwinist would be happy to appeal to purposefully guided mutations in order to explain this (or any) biological system. No Darwinist would say, "No problem. The official Darwinian definition of 'random' allows for the possibility that God (or someone) is guiding outcomes without using any physical mechanism." On the contrary, this is exactly the dilemma the Darwinist hopes to avoid.

A cautionary note: This discussion, like so many discussions involving God and evolution, risks giving the impression that there is good evidence that genetic mutations can build new biological systems, and we're just considering whether God could have guided them. There is no such evidence. We must avoid the temptation to move straight to reconciling Darwinian claims to theology without first evaluating the evidence for Darwinian claims.

In fact, based on the empirical evidence, I'm deeply skeptical that any series of genetic mutations alone, even if they are guided, can produce anything profoundly new (such as a new animal form or body plan), because there's far more going on in biology upstream from the DNA molecule. Just as you can't change the floor plan of a building by changing the color of the paint on the outside wall, you probably can't produce fundamentally new organisms with point mutations in DNA. Neo-Darwinism assumes that genetic mutations have all sorts of wonder-working powers since the theory needs a source of innovation of natural selection to preserve; but this is an assumption, not a dispassionate inference from empirical evidence.

For God to produce new biological forms, I suspect he would need to do much more than just coordinate genetic mutations. He would need to change things upstream, in the realm of epigenetic programming (to settle for a vague term). He would, to use a traditional term, need to provide a different form. If that's what has happened in the history of life, and organisms are, to some extent at least, the outcome of such divine activity operating outside of and in concert with material causes (of which he is also the source, given theism), then clearly the currently reigning theory of biological evolution would be incorrect.

Let's assume for a moment, however, that "random" in Darwinian evolution means only that an event is uncorrelated with any physical mechanism operating for the benefit of an organism. Given this definition, "Darwinism" and "current evolutionary science" would be compatible not just with intelligent design but with special creation, say, with God turning a small lizard into a flying bird in one generation by changing things upstream from the DNA and leaving evidence of his activity behind, as long as he didn't use a physical mechanism. If so, then even the most ardent special creationist can accept Darwinism and "current evolutionary science," and the most ardent Darwinist can also be a special creationist. This is implausible in the extreme, since special creationism was the explicit target of Darwin's critique in both the Origin and subsequent writings. No Darwin scholar would dispute this. So clearly we've taken a wrong turn somewhere.

Two Competing Visions of Science

Plantinga wants to show that not just "evolution" in the sense of common ancestry is logically compatible with Christian theism, and not just that selection and variation play some role in the process. He wants to show that Christian theism and Darwinism are compatible as well. This is understandable, since his goal is to show that "science" and theistic religion are compatible, and the standard understanding of biological evolution among scientists is Darwinian.7 Unfortunately, the reality is more complicated than that.

In historical biology at least, we're not just dealing with a metaphysically neutral "current science" and a pesky little metaphysical parasite that some folks mistake for the theory. We are dealing with two competing visions of the scientific enterprise, which are sown closely together. Christian theism is compatible with, and helped give rise to, the older, proper understanding of science. Natural science in its proper sense is the search for the truth about the natural world -- including true causal explanations -- based on hypothesis testing, systematic observation, and the like, no holds barred. Science, from scientia, means knowledge, so this is as it should be. As a result, any properly scientific theory of biological evolution will not decide ahead of time what types of evidence will be found, and what kinds of causal explanations will be permitted to explain that evidence. It will be open to all the evidence for the purpose of discovering the truth. Plantinga only needs to show that Christian theism is compatible with this proper understanding of science, and he does so successfully.

Unfortunately, in the nineteenth century, another, competing definition of science emerged. This is natural science as applied naturalism. According to this view, the proper scientific explanation is the best naturalistic explanation. (In a sense, this was the ratification of Bacon and Descartes' earlier call to purge "formal" and "final" causes from what we now call natural science, a call that had been imperfectly implemented prior to Darwin.) This view became especially prominent in biology with the emergence of Darwinism, which explicitly (and uncharacteristically for theories in natural science) sought to replace and exclude teleological explanations. Darwin's argument in the Origin, unlike most scientific theories, employed the premise "God wouldn't do things this way" throughout. This is why we are told that science must employ, not methodological neutralism, but methodological naturalism. In biology, that supposed methodological rule is cover for an intrinsically naturalistic theory. Christian theism is incompatible with science understood as applied naturalism, and a fortiori, it is incompatible with Darwinism, which is the most explicit form of this view of science.8

Equivocation between these two views of science serves the purposes of naturalists. When criticized by a smart philosopher or testy school board member for larding their theory with more metaphysical weight than is appropriate in a scientific theory, they can appeal to subtle definitions of words such as the definition of "random" offered by Elliott Sober. They can say that science is metaphysically neutral and not committed to naturalism. It is then accorded the respect enjoyed by science understood as a systematic search for the truth about the natural world. As soon as the philosophers and school boards go back to doing whatever they do, however, Darwinists drop the pretense and return to treating science as applied naturalism and denounce any suggestions of purpose or design in biology as anti-science, creationism, and all the rest.

Because of this rampant equivocation in the literature, it's very important to speak clearly on these matters and to avoid using non-representative definitions of words. We court trouble unless we use words such as "Darwinism" and "random" in their widely understood meanings. Moreover, the definitions should match the actual views of Darwin and those who follow him. The highly specialized definition of "random," for instance, which is compatible with God's guidance, just is not the Darwinian meaning of the word -- despite the fact that some Darwinian philosophers and biologists, in moments of caution or strategic cleverness -- have offered such a definition.

"Science"

The purpose of Plantinga's book is to show the compatibility between "science" and theistic religion. But there's a bit of an ambiguity running through Plantinga's references to "science," in part because the word itself is ambiguous. In most cases, context resolves the ambiguity. Still, at times, "science" seems to refer to the institution of natural science. Other times it seems to refer to a scientific theory, such as Neo-Darwinism. And at other times, it seems to refer to the relevant empirical evidence within a subdiscipline of science. I think what Plantinga wants to say (and certainly can say) is that theistic religion is consistent with the founding spirit of science, with the institution of science properly understood, with well-established scientific theories, and with the empirical evidence of science, including the evidence of biology. He can certainly say that no one is justified in claiming that the evidence shows that the origin and history of life is the result of a blind, unguided process. He can say all that without showing that Christian theism and "Darwinism" are compatible.

What to say about Darwinism? Maybe we should say that the naturalistic definition of evolutionary theory is not really science or that it is counterfeit science. Perhaps we should say the same thing about Darwinism. Perhaps Darwinism is similar to Marxism and Freudianism. It offers some interesting but minor insights into a domain of reality, but Darwinists have profoundly oversold their idea and have ended up distorting the empirical evidence in order to make it fit the theory. If so, perhaps we should say Darwinism is a scientific theory -- a theory within the natural sciences -- but not a good or well-established one.

Still, none of this changes the fact that Darwinism is the reigning view in modern biology. We can speak of guided and unguided evolution, but to speak of unguided Darwinism is a redundancy. We severely understate the problem if we treat the naturalistic part as just a superficial metaphysical parasite on an otherwise respectable and metaphysically neutral theory of evolution. It never was a parasite; it has been the beating heart of Darwinism since its inception.


Notes:

(1) In Mayr, Towards a new Philosophy of Biology: Observations of an Evolutionist (Cambridge: Harvard University Press, 1988), p. 98. I am not persuaded that Mayr's definition avoids the implication of a-teleology as Sober's does. Mayr's definition of "random" is inconsistent with God (for instance) directly causing genotypic changes to correlate with the adaptive needs of an organism apart from a physical mechanism. Although it doesn't strictly prevent God from acting, it circumscribes what he can do. If he acts for the adaptive needs of an organism, he must hide the fact that he is doing so. Sober's definition avoids this implication, so I go with his definition in the discussion.

(2) Sober, "Evolution Without Metaphysics?" in J. Kvanvig (ed.), Oxford Studies in Philosophy of Religion, vol. 3.

(3) For example, James Lennox, "Darwin was a Teleologist," Biology and Philosophy 8 (1993): pp. 409-421.

(4) In Charles Darwin, On the Origin of Species by Means of Natural Selection, 6th ed. Revised (London: John Murray,1872), p. 234; and Charles Darwin, The Variation of Animals and Plants under Domestication, 2 vols., 2nd ed., revised (New York: Appleton, 1883,) vol. 2, pp. 427-428. (1st ed. 1868). John Beatty treats the incident in detail in "Chance Variation: Darwin on Orchids," Philosophy of Science 73, no. 5 (2006): pp. 629-641.

(5) Herbert Spencer to A. R. Wallace, May 18, 1889, in James Marchant, Alfred Russel Wallace: Letters and Reminiscences (New York: Harper & Brothers, 1916), p. 301. Thanks to Michael Flannery for providing me with this reference and insight.

(6) For years, the National Association of Biology Teachers offered this definition of biological evolution: "[E]volution is understood to be the result of an unguided, unplanned process of random variation and natural selection." Under criticism from Alvin Plantinga and Huston Smith (a prominent religion scholar), the NABT dropped the words "unguided, unplanned," but the subsequent debate and discussion made it clear that that is still what they meant when talking about random variation and natural selection. See E.C. Scott (2008) "Science and Religion, Methodology and Humanism," at: http://ncse.com/ religion/science-religion-methodology-humanism.

(7) Some claim that "Darwinism" is a pejorative term made up by creationists. On the contrary, the term is frequently used to refer to the currently reigning theory of biological evolution. It is often called the "modern synthesis" of Darwin's original theory with genetics. Hence the term "Neo-Darwinism." For a recent example, see David J. Depew and Bruce H. Weber, "The Fate of Darwinism: Evolution After the Modern Synthesis," Biological Theory 6 (2011): pp. 89-102.

(8) Perhaps it's possible that natural science could be pursued along metaphysically neutral lines, conforming to what Plantinga has elsewhere called "Duhemian science." This "methodological neutralism," however, would restrict all sorts of questions from the domain of science that scientists constantly ask. Most historical and origins science would probably disqualify as science if we insisted on this approach. The more realistic approach, I think, is simply to accept that natural science is a complicated and diverse enterprise and that it sometimes bears on larger metaphysical questions. That's okay, as long as debatable metaphysical assumptions don't trump the empirical evidence, or become a justification for excluding evidence and arguments that have different metaphysical implications. In any case, it is methodological naturalism that often hides metaphysical naturalism, not methodological neutralism, with which we have to deal.

Photo credit: Niriel/Flickr.