Friday, December 26, 2008

God and philosophers II: The Design Argument

Here is the second part of the Boston Review article that focuses on the philosophical arguments for the existence of God (see the post about Ontological Argument here). Alex Byrne provides another excellent summary of the Design argument and objections associated with it. In particular, he does a great job of exposing problems with Intelligent Design and also the fine-tuning arguments (though there are subtle differences between the two and he points those out). Here is the full analysis of the Design argument:

Although the design argument can be traced to the ancient Greeks, it received one of its most careful and elaborate formulations from William Paley, an eighteenth-century English clergyman and philosopher, in his Natural Theology; or, Evidences of the Existence and Attributes of the Deity. That book was published in 1802, a few years before Paley’s death and more than half a century before the publication of Darwin’s On the Origin of Species.

Paley begins by contrasting the discovery of two objects while “crossing a heath”: a stone and a watch. The presence of the stone requires no explanation in terms of a designer—indeed, Paley supposes that the hypothesis that “it had lain there forever” might well be correct. The presence of the watch is another matter entirely, for on examination “we perceive—what we could not discover in the stone—that its several parts are framed and put together for a purpose, e.g. that they are so formed and adjusted as to produce motion, and that motion so regulated as to point out the hour of the day.” And the inference from these observed facts, Paley thinks, “is inevitable; that the watch must have had a maker.” Importantly, that is not because we know that watches are, in fact, usually the product of design: the conclusion, Paley says, would not be weakened if “we had never known an artist capable of making one.”

All that seems reasonable enough. The design argument that Paley then proceeds to give replaces the watch with terrestrial flora and fauna and their intricate parts. Paley—evidently a keen amateur naturalist—gives many examples, from the diverse mechanisms of seed dispersion to the tongue of the woodpecker, but his example of the eye is the one typically quoted. How could such a “complicated mechanism” have arisen, Paley asks, if not by the action of a designer? “In the human body, for instance, chance, i.e., the operation of causes without design, may produce a wen, a wart, a mole, a pimple, but never an eye.” In the case of the watch, the reasonable conclusion is that a designer produced it. And similarly, Paley thinks, in the case of the eye and other biological structures. Admittedly, we have no idea how the designer managed to construct the eye, and we have “never known an artist capable of making one.” As Paley says, however, these points of disanalogy do not seem to ruin the argument.

Unlike the ontological argument, the design argument is not supposed to prove God’s existence. Rather, it is an “inference to the best explanation,” like the inference that there are mice in the kitchen because this hypothesis best explains the missing cheese. The hypothesis of a designer is one of many possible “scientific explanations” of Paley’s watch on the heath, and similarly of the eye. The frequent complaint that intelligent design is “not science” (as opposed to “bad science”) only succeeds in muddying the waters.

An inference to the best explanation can be overturned by more evidence. Perhaps, on further investigation, it turns out that another hypothesis—say, that the au pair has been snacking in the early hours—is the best explanation of the missing cheese. And that is the standard reply to Paley: we now know that the best explanation of the apparent design of the eye is not “the hand of an artificer,” but Darwinian evolution. To borrow from the title of an earlier book by Dawkins, a blind watchmaker—the impersonal forces of natural selection—made the eye.

This reply crucially hinges on the assumption that modern biology can explain all instances of apparent design, and it is here that sophisticated proponents of intelligent design, most notoriously the biochemist Michael Behe, have seen an opportunity to dust off and burnish Paley’s argument.

In his first book, Darwin’s Black Box, Behe argues that while evolution by natural selection “might explain many things,” it cannot explain what he calls “irreducible complexity.” The notion is straight out of Paley, who writes of the watch that “if the different parts had been differently shaped from what they are, or placed after any other manner or in any other order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it.” A watch is “irreducibly complex” in the sense that many of its main parts are essential to its proper functioning—remove the balance wheel, or the escapement, and all you have left is a paperweight. Irreducible complexity is everywhere in nature: Behe’s poster children are the blood-clotting system and the bacterial flagellum, but he also quotes Paley’s observation that “The heart, constituted as it is, can no more work without valves than a pump can.” According to Behe, a process of small step-by-step alterations of the sort found in natural selection is wildly unlikely to produce irreducibly complex systems.

Obviously it is a matter of great importance whether Behe’s criticism of the cornerstone of modern biology is correct. (For a clear explanation of why it isn’t, see H. Allen Orr’s review of Behe’s book in Boston Review, December 1996/January 1997.) But here the debate took a crucial turn too hastily: focusing attention on whether evolution by natural selection can explain the origin of the bacteriological flagellum is to obscure the fact that the design argument fails even if Behe is right.

David Hume’s Dialogues Concerning Natural Religion (published posthumously in 1779) presented the key objections, more than twenty years before Natural Theology. Two of Hume’s objections are especially acute. First, if the argument works at all, its conclusion is much weaker than might have been hoped. The argument does not indicate anything about what the designer is like: whether it is benevolent or a suitable object of worship. Even the intelligence of the designer is up for grabs—terrestrial biology might be the product of long trial and error, with the designer’s many previous attempts “botched and bungled.” Or perhaps the designer is “a stupid mechanic,” who imitated other much cleverer designers who practiced their art in far-off galaxies. Further, the designer could have died long ago—the eye and such might have been “the production of old age and dotage in some superannuated deity.” And finally, since the design of something complicated is usually a collective endeavor—“A great number of men join in . . . framing a commonwealth,” for example—we can hardly presume that there was exactly one designer. At best, the design argument shows that some designer or designers, whose motives, talents, and present whereabouts are all unknown, existed at some time. The proponent of the argument is at liberty afterwards “to fix every point of his theology, by the utmost license of fancy and hypothesis.” Perhaps life on Earth was designed over millions of years by successive committees of incompetent and thoroughly despicable space aliens, who are now fortunately all dead.

Paley had read Hume, and he tries to reply to this objection. Paley concedes that if the design argument simply concerns individual biological structures like the eye, then the proper conclusion is indeed weak: “there must have existed, at some time and at some place or other, an artificer or artificers.” However, he thinks a more careful study of the biological world as a whole reveals that there is exactly one designer (or at any rate one chief architect), who possesses the usual divine attributes. But Paley’s arguments on this score are feeble. He notes the general similarities in the body-plans of animals, and concludes that this “bespeaks the same creation and the same Creator,” forgetting Hume’s point that multiple designers can act in concert, or that one designer can pick up where another left off. And in support of the goodness of the deity, Paley declares, “It is a happy world after all.” Rural England is, anyway: “A bee amongst the flowers in spring is one of the cheerfullest objects that can be looked upon.” A more plausible theological conjecture is the remark attributed to the biologist J. B. S. Haldane, that the creator had “an inordinate fondness for beetles.”

Hume’s first objection is that the design argument can only establish the existence of at least one designer. His second objection is that the argument does not establish even this much. Paley claims that the evidence points to the conclusion that, by means entirely unknown, the biological world is the product of design. But why favor this over the hypothesis that, also by means entirely unknown, flora and fauna were produced by, as Paley puts it, “the operation of causes without design”?

As Paley himself emphasizes, his initial watch analogy is far from perfect: watches, unlike organisms, do not reproduce. The eye has not been found lying on its own on the heath, but in the bodies of countless creatures and their ancestors. And offspring differ in various ways from their parents. So one possibility is that the operation of causes without design, operating over “a hundred millions of years,” somehow allows, after numerous generations, a “round ball” to “acquire wings,” eyes, and so forth. Paley’s strategy for dismissing no-design alternatives wholesale is to object to the specific evolutionary theories of his day (for instance that of Erasmus Darwin, Charles’s grandfather). But this is rather like saying that because this apple and that pear are rotten, vegetables are better than fruit. What Paley needs is an argument for choosing the general hypothesis of an unknown designer or designers operating by unknown means over the general hypothesis of an unknown blind process operating by unknown means, and he signally fails to supply one.

An example that briefly appears in Darwin’s Black Box nicely illustrates the point. In 2001: A Space Odyssey, a magnetic anomaly in one of the moon’s craters leads to the discovery of a perfectly regular slab buried under lunar soil. The characters have no idea how the slab was constructed, or what it is for, and have never known an artist capable of making one; nevertheless they reasonably conclude that it was designed. But that is precisely because the characters are not in Paley’s position. They know enough about lunar geology, astronomy, and the possibility of extraterrestrial life to discredit the rival hypothesis that the monolith is a natural object (a big crystal, say) that formed on the moon or collided with it. Paley, on the other hand, had no reason, other than the failure of his imagination, to dismiss the hypothesis of “causes without design.”

Darwin’s Black Box exactly recapitulates Paley’s mistake. “Might there,” Behe asks after he has disposed of Darwin’s theory, “be an as-yet-undiscovered natural process that would explain biochemical complexity?” Assuming for the sake of the argument that Darwinism is false, Behe is surely right that “if there is such a process, no one has a clue how it would work.” But of course that is quite different from saying that there is no such process. Moreover, intelligent design is in the very same boat: if there is such a process, no one has a clue how it would work either. Why is one mysterious unknown process to be favored over another? After all, as Behe clearly brings out, biochemistry is fantastically baroque, with many unanswered questions and unsolved problems.

Read the full article here. I will include the fine-tuning arguments in the next post.