Irreducible Complexity

Irreducible Complexity (IC) is the idea that certain systems are made up of a number of integrated parts, such that the removal of one of those parts will prevent the function of the system. This could mean that a system also has parts that can be removed without losing the primary function, but it has an IC core of parts that are necessary. A car would be an example; you can remove a windscreen wiper and it will still go. Remove the battery, and it will not. The battery is part of the IC core.

The concept of IC was first presented by Michael Behe in 1996 in his book Darwin's Black Box (though he had previously discussed an embryonic form of the argument in the creationist textbook Of Pandas and People). He defined it:

By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional.

The important point to note in that definition is that IC only refutes direct evolutionary routes. I am told Behe argues that other routes are "improbable" but whether that means 1 chance in 3 or 1 chance in a billion I do not think anyone has any idea. The usual tactic for IDists is to demand that the evolutionists do the hard work and determine the probabilities. In any event, I am not aware of anything by Behe that would lead us to suppose that non-direct routes could not cause these IC systems.

This is odd, as it leaves his argue looking a bit stupid:

1. IC systems exist in nature
2. IC systems cannot evolve by a direct route, but they could evolve indirectly
3. Given that IC systems might or might not have evolved, it follows that they must be designed

Point 3 is clearly nonsense.

But here is the trick; Behe uses another definition when it suits him. Here is an article by Behe himself, hosted at ARN. From it:

A system which meets Darwin's criterion is one which exhibits irreducible complexity. By irreducible complexity I mean a single system which is composed of several 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. An irreducibly complex system cannot be produced gradually by slight, successive modifications of a precursor system, since any precursor to an irreducibly complex system is by definition nonfunctional. Since natural selection requires a function to select, an irreducibly complex biological system, if there is such a thing, would have to arise as an integrated unit for natural selection to have anything to act on. It is almost universally conceded that such a sudden event would be irreconcilable with the gradualism Darwin envisioned.

Hmm, that sounds a little stronger than his previous claim. Now he is claiming that there are no evolutionary routes to an IC system at all! He continues:

The components of cilia are single molecules. This means that there are no more black boxes to invoke; the complexity of the cilium is final, fundamental. And just as scientists, when they began to learn the complexities of the cell, realized how silly it was to think that life arose spontaneously in a single step or a few steps from ocean mud, so too we now realize that the complex cilium can not be reached in a single step or a few steps. But since the complexity of the cilium is irreducible, then it can not have functional precursors. Since the irreducibly complex cilium can not have functional precursors it can not be produced by natural selection, which requires a continuum of function to work. Natural selection is powerless when there is no function to select. We can go further and say that, if the cilium can not be produced by natural selection, then the cilium was designed.

How interesting. So now the argument is:

1. IC systems exist in nature
2. IC systems cannot evolve by any route
3. Given that IC systems could not have evolved, it follows that they must be designed

Now at least his argument makes a bit more sense. However, this leaves a couple of problems. The first for us is that apparently Behe accepts evolution - not modern evolutionary theory (MET), but universal common descent at least, and presumably much of MET. How does he reconcile that with his IC claims? I have no idea.

The second problem is for Behe. In this alternative definition, how on Earth does he go about proving that an IC system cannot arise via an indirect route? How can he show that point 1 is true?

What a lot of IDists do (and I have no reason to suppose Behe is guilty of this) is to quietly flip from one definition to the other.

1.IC systems (definition 1) exist in nature
2. IC systems (definion 2) cannot evolve by any route
3. Given that IC systems could not have evolved, it follows that they must be designed

The IDEA Center describe themselves thus: 

The Intelligent Design and Evolution Awareness (IDEA) Center is a 501 (c)(3) non-profit organization dedicated to promoting intelligent design theory and fostering good - spirited discussion and a better understanding over intelligent design theory and the creation - evolution issue among students, educators, churches, and anyone else interested

An organisation dedicated to a better understanding of ID. Perfect. These guys will surely know about IC and its implications. Right? So how do they describe IC?

Darwin, meet Michael Behe, biochemical researcher and professor at Lehigh University in Pennsylvania. Michale Behe claims to have shown exactly what Darwin claimed would destroy the theory of evolution, through a concept he calls "irreducible complexity."
…
Darwin recognized this as a potent threat to his theory of evolution-the issue that could completely disprove his idea. So the question must be raised: Has Darwin's theory of evolution "absolutely broken down?" According to Michael Behe, the answer is a resounding "yes."

Now as far as I can see, the IDEA center is using exactly this definition flipping here.

For completeness, Behe has a third definition:

An irreducibly complex evolutionary pathway is one that contains one or more unselected steps (that is, one or more necessary-but-unselected mutations). The degree of irreducible complexity is the number of unselected steps in the pathway.

This is not so far from the first, as both concentrate on one specific evolutionary route. The task for Behe must be to eliminate every route possible (which may well be more than every route he can think of) to prove the system did not evolve. Then again, Behe accepts evolution, so I guess he will not bother...

One of the examples of an IC system that Behe presents in his book is the immune system. He says (quoted from here):

We can look high or we can look low, in books or in journals, but the result is the same. The scientific literature has no answers to the question of the origin of the immune system

These words came back to haunt Behe at the 'Kitzmiller et al. v. Dover Area School District' court case (as describe in an article in Nature):

Then, 10 days later, Behe took the stand. During cross-examination by the plaintiffs' lead counsel Eric Rothschild, Behe reiterated his claim about the scientific literature on the evolution of the immune system, testifying that "the scientific literature has no detailed testable answers on how the immune system could have arisen by random mutation and natural selection." Rothschild then presented Behe with a thick file of publications on immune system evolution, dating from 1971 to 2006, plus several books and textbook chapters. Asked for his response, Behe admitted he had not read many of the publications presented (a small fraction of all the literature on evolutionary immunology of the past 35 years), but summarily rejected them as unsatisfactory and dismissed the idea of doing research on the topic as "unfruitful."

And so ID rejects real science.

There is, however, another dodge up Behe's sleeve which lets him maintain his delusion.

Behe has proposed a number of IC systems, the immune system being another. When it was pointed out in the Kitzmiller trial that actually biologists have a fair idea of how it evolved, he hid his God in the gaps. There were still bits that were not fully understood, and that is where his God is lurking. When asked what would convince him otherwise, he said:

Not only would I need a step-by-step, mutation by mutation analysis, I would also want to see relevant information such as what is the population size of the organism in which these mutations are occurring, what is the selective value for the mutation, are there any detrimental effects of the mutation, and many other such questions.

He is so desperate to cling to his pet theory that he admits only the most detailed evolutionary process would convince him he is wrong. Compare to the alternative that ID offers - there was an intelligent design who did it, we refuse to consider the nature of the designer or how it was done or when it was done.

Further resources:
http://en.wikipedia.org/wiki/Irreducible_complexity
http://www.talkdesign.org/faqs/icdmyst/ICDmyst.html