Last week, I wrote an article highlighting the irreducible complexity of the DNA replisome. A reader wrote to the Center for Science and Culture asking whether the complexity of the DNA replisome could in fact be used as an argument against intelligent design. Since the role of topoisomerase enzymes is to undo an undesirable effect of the helicase (i.e., to remove supercoils caused by the torsional stress), the reader suggested that the system could have been designed in a simpler way — that is, by designing the helicase such that it avoided the problem in the first place. Thus, so the objection goes, the complexity of DNA replication is in excess of what it needs to be, and this is better predicted supposing intelligent design to be false. Since this is not the first time that I have encountered this sort of objection, I thought I would offer a brief response here.

On Closer Inspection

In my view, this is an incredibly weak argument. There are always alternative ways that one can envision in which an engineered system might have been designed differently. Having no experience of designing living organisms ourselves, we should exercise tremendous caution about asserting what a designer should or should not have done. We do not even know what an alternative design would look like, nor whether it in fact would be less complex and more efficient than the actual system. More interesting is the question of what the designer in fact did. The challenge to incremental evolutionary processes does not disappear in light of this question.

Often these claims that “no designer would have done it that way” dissolve on closer inspection. Witness the statement that the backwards-wiring of the vertebrate retina is “poor design,” with blood flow plugged into the back of the retina, forcing the optic nerve to extend out over the retina. However, this argument is refuted by observing that any tradeoffs are fully compensated by special Müller cells which function like fiber-optic cables to channel light directly onto the retina.

Epistemic Asymmetry 

But assume for the sake of the argument that those “poor design” arguments hold some degree of merit. We must then recognize that the design hypothesis has far greater resources to explain why DNA replication was designed one way versus another than does naturalism to account for the origins of the complex and integrated arrangement of parts necessary for DNA replication to work. Therefore, at best, the concern the reader has raised is only weak evidence relative to the case (made in my previous article) that unintelligent mechanisms (i.e., processes lacking foresight) are causally inadequate to explain the origins of DNA replication. 

This is an example of what I call epistemic asymmetry — that is, where examples of evidence on one side of the scale are individually of greater weight than examples of the counter-evidence on the other side of the balance.