Anyone reading Michael J. Behe’s Darwin’s Black Box (1996) who ever took a university course in the philosophy of religion might be forgiven for thinking that Behe’s central argument for “intelligent design” seemed familiar. Isn’t it a reiteration of the central argument in William Paley’s classic Natural Theology (1802), only at the cellular level? Paley in miniature, as it were, or Paley writ small?
After all, Paley famously asked his readers to imagine finding a stone and a watch on a heath. While the presence of the stone would require no special explanation, he argues, the presence of the watch would, for:
when we come to inspect the watch, 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; that, if the different parts had been differently shaped from what they are, of a different size 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.
The watch exhibits, that is, what Behe dubbed irreducible complexity: it is “composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.”
The term, by the way, was not original with Behe. Stephen Jay Gould, of all people, used “irreducible complexity” in a 1985 essay, reprinted in Bully for Brontosaurus—though not in Behe’s sense. Michael J. Katz used the term, in more or less Behe’s sense, in his 1986 book Templets and the Explanation of Complex Patterns, although when I corresponded with him in 2002, he was not enthusiastic about Behe’s use of it.
Anyhow, it’s not surprising that readers were quick to associate Behe’s argument with Paley’s. Taking a case practically at random, in 1998, the biochemist Bruce H. Weber wrote, “Michael Behe restates in modern biochemical terms William Paley’s argument that there is an irreducible functional complexity to living beings that suggests the action of a designer-creator.”
In a 2001 paper, “The Modern Intelligent Design Hypothesis,” Behe himself attempted to distinguish his argument from Paley’s, writing, “The most important difference is that my argument is limited to design itself; I strongly emphasize that it is not an argument for the existence of a benevolent God, as Paley’s was.” But that’s a difference in the ambition; unmentioned are any differences in the argument for design per se.
A while ago, I was rereading Natural Theology in order to review a new edition of it for the philosophy journal Sophia, and I marked a passage that clearly shows a divergence between Paley’s and Behe’s arguments:
Nor, thirdly, would it bring any uncertainty into the argument, if there were ... some parts, concerning which we could not ascertain, whether they conduced to that effect in any manner whatever. For ... [if] there were parts which might be spared, without prejudice to the movement of the watch, and that we had proved this by experiment,—these superfluous parts, even if we were completely assured that they were such, would not vacate the reasoning which we had instituted concerning other parts. The indication of contrivance remained, with respect to them, nearly as it was before.
Here Paley is suggesting that irreducible complexity isn’t the only, just the best, indicator of design. In contrast, although Behe isn’t committed to irreducible complexity as the only indicator of design, his argument clearly fails for systems that lack it.
(Speaking of the new edition of Natural Theology, let me recommend it wholeheartedly. Although the text is widely available on-line, it’s still worth your while to buy the book. As I wrote in my review, “Meticulously edited with a host of notes and a copious bibliography, Eddy and Knight’s edition is sure to become the new standard scholarly edition of what is a historically, theologically, and philosophically important work.”)
In retrospect, it isn’t surprising that Paley didn’t anticipate Behe in arguing from irreducible complexity. Behe’s argument is aimed at the use of natural selection in explaining biochemical systems like the bacterial flagellum and the vertebrate blood-clotting cascade. To have even a prayer of success, it needed to focus specifically on a class of systems for which (supposedly) no such explanation could work.
No such explanation was even on offer in Paley’s day, although there were glimmerings of it, of which Paley was aware. After considering and swiftly rejecting the appeal to brute chance, he considers the appeal to chance plus selection:
There is another answer which has the same effect as the resolving of things into chance: ... that the eye, the animal to which it belongs, every other animal, every plant, indeed every organized body which we see, are only so many out of the possible varieties and combinations of being, which the lapse of infinite ages has brought into existence; that the present world is the relict of that variety: millions of other bodily forms and other species having perished, being by the defect of their constitution incapable of preservation, or of continuance by generation.
Paley’s rejoinder to the protoevolutionary account he sketched? “Upon the supposition here stated, we should see unicorns and mermaids, sylphs and centaurs, the fancies of painters, and the fables of poets, realized by examples.” Alas.
Here’s a counterfactual to ponder. If Paley had been aware of evolutionary theory, would he have refined his argument, contending (mistakenly) like Behe that irreducible complexity entails unevolvability? Or would he have taken evolution in stride? After all, Paley was not guilty of misrepresenting the established science of his day in order to extract conclusions that were amenable to his antecedent theological beliefs.