Why Behe offered a second definition of IC

[swamidass (S. Joshua Swamidass)]

@Bilbo

By irreducibly complex I mean a single system which is composed of several well-matched, interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning.
(Behe 1996, 39)

While I think that’s a reasonable definition of IC (IC1 in our parlance), and it gets across the idea to a general audience, it has some drawbacks. It focuses on already-completed systems, rather than on the process of trying to build a system,

In this quote, he abandons IC1 as a scientifically rigorous idea, identifying it as merely a useful convenience when discussing it with the public. He also discusses its “drawbacks.” (what are they?)

@Bilbo

While thinking of Keith Robison’s scenario, I was struck that irreducible complexity could be better formulated in evolutionary terms by focusing on a proposed pathway, and on whether each step that would be necessary to build a certain system using that pathway was selected or unselected.

Here, he points out that he has a new and better formulation of IC (IC2 in our parlance). He calls it a better formulation, except it is also a different concept.

IC1 is not the same thing as IC2. IC2 is not a better formulation of IC1. IC1 is clearly falsified, and Behe is not defending it as a valid concept here.

To be clear, IC2 has major problems too:

@swamidass

Still, for the IC2, most knowledgeable scientists agree that IC2 systems exist in nature too. Similar to IC1 systems, we are convinced that evolution can evolve IC2 systems also. Embedded in this definition is an important straw man. He writes “one or more unselected steps.” Here, into the IC2 definition is being smuggled a strict enforcement of “Darwinian” evolution. Now, anyone following biology at a basic level of competence knows that strict-Darwinian evolution was falsified a long time ago, in the 1970s. We now know that a large proportion of changes are near neutral or even slightly deleterious in the short term. So this dominant pathway of change is intrinsically ruled out by Behe’s definition.

Nothing new here @Bilbo. Though I do appreciate the new thread on with the extended quote. Makes it clear what the issue is.