Shanks and Joplin (RNCSE 2000; 20 [1–2]: 25–30) disputed Michael Behe's irreducible complexity challenge to evolution, arguing that there was at least one way for evolutionary change to accomplish this task. Their article prompted a response from Michael Behe, and a reply from Shanks and Joplin.
In their article "Of mousetraps and men: Behe on biochemistry" (RNCSE 2000; 20 [1–2]: 25–30), which has just come to my attention, Shanks and Joplin appear mistakenly to attribute to me the contention that irreducibly complex biochemical systems must have been created ex nihilo. I have never claimed that. I have no reason to think that a designer could not have used suitably modified pre-existent material. My argument in Darwin's Black Box was directed merely toward the conclusion of design. How the design was effected is a separate and much more difficult question to address. Although creation ex nihilo is a formal possibility, design might have been produced by some other means that involved no discontinuities in natural law, even if the designer is a supernatural being.
One possibility is directed mutations. As noted by Brown University biologist Kenneth Miller in Finding Darwin's God (New York: HarperCollins, 1999), "[t]he indeterminate nature of quantum events would allow a clever and subtle God to influence events in ways that are profound, but scientifically undetectable to us. Those events could include the appearance of mutations..." (p 241). I have no reason to object to that as a route to irreducibly complex systems. I would just note further that such a process amounts to "intelligent design", and that while we may be unable to discern the means by which the design is effected, the resultant design itself may be detected in the structure of the irreducibly complex system.
The core claim of intelligent design theory is quite limited. It says nothing directly about how biological design was produced, who the designer was, whether there has been common descent, or other such questions. Those can be addressed separately. It says only that design can be empirically detected in observable features of physical systems. As an important corollary, it also predicts that mindless processes such as natural selection or the self-organization scenarios favored by Shanks and Joplin will not be demonstrated to be able to produce irreducible systems of the complexity found in cells.
A traditional Christian explanation of the origin of things is supernatural design and creation ex nihilo. We are grateful for Michael Behe's suggestion that we give consideration to alternative hypotheses concerning design — perhaps through the modification of pre-existing materials. Behe cites Kenneth Miller, who asks us to envision supernatural intelligent design proceeding by some cunning manipulation of events at the quantum level "scientifically undetectable to us."
The qualification that the way design is effected be "scientifically undetectable to us" is crucial. The trouble here is that there is an infinity of alternative design hypotheses (one designer did it, two designers did it, three did it, and so on), and an imaginative theorist could no doubt come up with many design scenarios, all of which are scientifically undetectable to us. Being scientifically undetectable, they are, of course, evidentially ungrounded.
Notwithstanding this, Behe's central claim is that the fact of design (regardless of how it was effected) can be empirically detected in observable features of physical systems. Such features cannot be explained, he contends, on the basis of mindless natural processes. In our earlier essays on Behe's ideas, we introduced the idea of biochemical redundant complexity. A redundantly complex biochemical system is one that contains redundant subsystems — subsystems that can be removed without complete loss of function achieved by the system as a whole. Behe has conceded the existence of redundant complexity (see his "Self-organization and irreducible complexity: A reply to Shanks and Joplin," Philosophy of Science 2000; 67: 155–62).
The admission is crucial. Reduce the redundancy in a redundantly complex system to the point where the further removal of a subsystem causes the system as a whole to lose function completely, and a redundantly complex system has evolved into an irreducibly complex system. Irreducibly complex systems are thus limiting cases of redundantly complex systems. Mutations resulting in gene duplication can give rise to redundancy. Mutations transforming functional genes into pseudogenes can reduce redundancy to the point where a system once manifesting redundant complexity is now irreducibly complex. (An extended discussion of these ideas can be found in our essay, "Behe, biochemistry, and the invisible hand", Philo 2001; 4: 54–67). There is no need for any additional mechanisms and agents, be they supernatural or merely of the space alien variety, that are scientifically undetectable to us. Contrary to Behe, the design hypothesis cannot simply be validated by pointing to physical systems manifesting irreducible complexity.