Joined: Jan. 2006
I've puzzled for a couple three years now over what 'irreducible complexity' might mean.
First, people said you'd expect the standard definition ("all parts required") to describe a pretty sizeable precentage of organisms, since nature always seems to find some functional application of any useful redundency. Behe said that didn't count; somehow just because an organism can't survive without all its parts doesn't make it IC (whatever that might mean).
Next, people pointed out the 'scaffolding' process by which structures no longer necessary for a changed lifestyle are discarded. Parasites were common examples. Behe said that didn't count, he was talking about someting evolving by adding and not losing stuff.
Next, people pointed out what Gould (and Judge Jones) called exaptation - the adaptation of some structure to another use. Behe said that didn't count, he was talking about adding structures without changing their application.
Next, people pointed out that the same function is performed in different organisms by less complex structures. Behe said that didn't count, those were *different* IC systems.
Next, people pointed out that the same function is performed in very similar organisms by essentially the same system, but still lacking one or more parts. Behe said that didn't count, by redefining what a 'part' is. It could be anything from an organ down to an amino acid, whatever Behe decided the system couldn't work without.
Next, people pointed out that we have enough historical data to show how Behe's IC systems actually evolved. Behe said that didn't count unless you could produce hard evidence of every molecular change leading to his selected structures, for every ancestor back to the original life.
Apparently, Behe's model of evolution is that there's a vast inventory of existing "parts" out there, available to be bolted on as though evolution worked like making widgets on an assembly line. In fact, the assembly-line model is the ONLY model Behe will allow. Removing parts not allowed, morphing parts not allowed, functional change not allowed, lifestyle change not allowed, even direct refutations based on what IS allowed are not allowed!
So we finally reach the end of the road: for Behe, IC systems are systems that could not have evolved according to the only evolutionary path he is willing to recognize, which just happens to be a path evolution does not follow because it's not possible. All other paths are ruled out.