Behe's Critics' Scaffolding Falls Down

In their response to Michael Behe in Quarterly Review of Biology, Maarten Boudry, Stefaan Blancke, and Johan Braeckman raise a common objection to irreducible complexity, claiming that even if an irreducibly complex system cannot function if it loses parts, it might still function if it gains parts. The problem is that this "scaffolding" argument lacks biological analogues.

If we trace backward along the evolutionary pathway, perhaps the system first gains parts until there is a sort of...