Here is the second installment of notes on Paul Draper's important article critiquing Behe's design argument, "Irreducible Complexity and Darwinian Gradualism: A Reply to Michael J. Behe", Faith and Philosophy 19:1 (2002), pp. 3-21
Draper points out that three common criticisms of Behe's irreducible complexity argument miss the mark.
I. Bad Objection #1: Other Biochemical Systems are Reducibly Complex and Evolvable
First, some have argued that lots of biochemical systems exhibit redundancy, which shows that such systems are not irreducibly complex. But Draper points out that this doesn't refute Behe's argument. For recall that Behe isn't committed to the claim that all biochemical systems are irreducibly complex, but rather the weaker claim that at least some are, and that some of these (viz., those that are very complex) could not have evolved through gradualistic evolutionary processes. Behe isn't your standard creationist: he thinks the evidence for the key evolutionary theses of common ancestry and descent with modification are persuasive. He also thinks that gradualistic evolutionary mechanisms can account for many biochemical structures as well -- viz., those that are reducibly complex. But the authors in question don't address the particular examples of biochemical systems that Behe argues are irreducibly very complex (e.g., the bacterial flagellum).
II. Bad Objection #2: Very Simple Irreducibly Complex Systems are Evolvable
Second, a number of people -- most prominently, cell biologist and devout Catholic Kenneth Miller -- have argued that certain structures are irreducibly complex, and yet have clearly evolved gradually. So, for example, MIller points out that the three-boned structure within the inner mammalian ear is irreducibly complex, and yet we have excellent evidence that it evolved via an indirect evolutionary pathway from parts of the jaws of reptilian evolutionary predecessors. But this doesn't refute Behe's argument, either. For recall that Behe argues that while no irreducibly complex system can evolve via a direct evolutionary pathway, he grants that a relatively simple irreducibly complex structure can evolve via an indirect evolutionary pathway: "Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitively rule out the possibility of an indirect, circuitous route. As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously." Behe, Darwin's Black Box, P. 40.
In short, the first two popular criticisms of Behe's argument miss the mark. For these are based on examples of reducibly complex systems and simple irreducibly complex systems that have arisen via gradualistic evolutionary pathways. But to touch Behe's argument, one needs an example of an irreducibly very complex system that has arisen via a gradualistic evolutionary pathway.
III. Bad Objection #3: It's Just Paley's Bad Analogical Design Argument in New Packaging
Finally, a number of people have claimed that Behe's argument is just a re-statement of Paley's design argument, and since Paley's version falls prey to Hume's and Darwin's criticisms, so does Behe's. But Draper argues that while Behe has contributed to this perception (he explicitly identifies his argument with Paley's), it is nonetheless a misleading and uncharitable criticism. This is because most people think of Paley's argument as the one Hume attacked, viz., an argument from analogy, and having the following form:
1. Human artifacts are intelligently designed.
2. The universe, or some of its parts, resemble human artifacts.
3. Therefore, the universe, or some of its parts, were (probably) intelligently designed.
But as Elliot Sober has argued, while Paley talked about an analogy between watches and organisms, his actual argument wasn't itself an argument from analogy. Rather, it was an abductive argument to the best available explanation:
1. Some natural systems (e.g., the human eye) are mechanically ordered (i.e., they exhibit the same sort of order as watches and other machines produced by human beings).
2. Intelligent design is a very good explanation of mechanical order.
3. No other explanation (or no equally good explanation) of mechanical order is available.
4. Every instance of mechanical order has an explanation.
5. So, some natural systems were (probably) intelligently designed.
But if so, then at least three things can be said on behalf of Behe in response to the third criticism. First, while the critics may be right that Hume refuted the analogical version of the design argument, they're wrong to think that Hume refuted Paley's design argument. For his is the abductive version, and Hume's criticisms don't refute it. And if Behe is defending Paley's abductive argument, it follows that it's not enough to point to Hume to answer Behe's argument.
Second, Behe has made a genuine contribution to improving Paley's argument by articulating an account of mechanical order mentioned in the premises, viz., his notion of irreducible complexity.
The previous point brings us to the third. For while many would argue that Darwin refuted Paley's abductive argument (even if Hume did not), Behe has strengthened Paley's argument in a way that requires more of a response than just pointing to Darwin. For Darwin and subsequent scientists have only shown how biological systems larger than biochemical structures can evolve gradually. But that's consistent with the claim that the smaller, biochemical structures cannot evolve gradually. And as we saw in a previous post, Behe has argued just this: certain biochemical structures (e.g., the bacterial flagellum) are irreducibly very complex, and thus couldn't have arisen via direct or indirect evolutionary pathways. Therefore, we have another reason for thinking that Behe's argument can't be dismissed by just pointing to earlier critiques of the design argument.
We've just seen three common criticisms of Behe's argument that don't seem to work. In the remaining posts in this series, we'll take a look at three criticisms that seem telling.
 Philosophy of Biology (Boulder, CO: Westview Press, 1993), pp. 34-35. Draper's reference, "Irreducible Complexity and Darwinian Gradualism", p. 7.
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