Irreducible complexity is an argument given to us by Michael Behe. In brief, he claims that some bio-molecular systems cannot have evolved gradually. From this failure of imagination he makes the argument from ignorance that a 'designer' - a deus ex machina, is required to solve the dilemma.

While Behe if often credited with the idea, I thought it interesting to note that Charles Darwin not only predicted the concept of Irreducible complexity, he also refuted it.... on the same page.

From page 159 of the Barnes and Noble edition of The Origin of the Species, Darwin first touches upon the notion of Irreducible complexity:

"If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."

He then refutes it in a manner that still stands:

"We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind. Numerous cases could be given amongst the lower animals of the same organ performing at the same time wholly distinct functions... in such cases natural selection might easily specialize, if any advantage were thus gained, a part or organ, which had performed two functions, one function alone, and thus wholly change its nature by insensible steps. two distinct organs sometimes perform simultaneously the same function in the same individual, to give on instance, there are fish with gills, at the same time they breathe free air in their swimbladders... one of the two organs might with ease be modified and perfected so as to perform all the work by itself, being aided during the process of modification by the other organ; and then this other organ might be modified for some other quite distinct purpose, or be quite obliterated.

The illustration of the swimbladder in fishes is a good one because it shows us clearly the highly important fact that an organ orginally constructed for one purpose, namely flotation, may be converted into one for a wholly different purpose, namely respiration."

Today, we call this concept "exaptation". In exaptation, a precursor system evolves for a different function, or a series of precursor systems, cobbled together, form to serve a new function.

Michael Behe was refuted 93 years before he was born.

Seeing as few theist arguments commit only one error, I'd now like to look at seven key problems with Behe's argument.

Problem 1

In investigating a biological entity to make his irreducible complexity argument, Behe works backwards – looking at complex systems and then removing parts in order to show that the system could not work without them. This is a process called "ablation". Ablation is an intuitive process: children use this method to learn about objects. A child may take a phone apart to see how the phone works in the absence of that particular part. A loss of a particular function is used as a pointer to the part's function.

Working 'backwards' in this fashion isn't a problem as long as you remember that things don't evolve 'backwards'. This in itself might seem a simple matter.... but observe: a very subtle mindset enters the picture when we work backwards: we begin to observe the present function of a part as the 'goal' of the evolutionary process.

Therefore, by working backwards, Behe admits that he creates the illusion that the function of the system is the ‘goal’ of the system. Yet evolutionary theory is not eschatological - systems are not goal oriented; they exist due to random mutation, and they continue to exist because they allow the life form to procreate successfully, as per natural selection.

Therefore, Behe himself admits that the mindset he uses to make the Irreducible complexity argument introduces a false sense that biological entities have 'goals' or purposes'. Yet Behe's entire argument is that some biological entities are designed! For Behe to argue that there is intelligent design, he has to prove that there is purpose. Yet he has never proven any such thing; ‘purpose’ is only an illusion born of his Backward thinking, which in turn, is a function of his dogmatic presupposition that there is a designer.

Problem 2

Behe concedes that there is a more parsimonious solution to the problem of irreducibly complex systems - the process of "Exaptation". An ‘irreducibly complex system could have evolved from an indirect circuitous route – a precursor system that evolved for a different function, or a series of precursor systems, cobbled together, for a new function. Behe discusses this problem in page 40 of his book: The Black Box.

Problem 3

Behe admits that organisms with non functioning complex systems could still live and procreate. This admission alone is all that is required to refute his argument.

Problem 4

Behe concedes that intelligent design does not offer a working model of how ID works. It merely is an argument from ignorance - an inability to understand how a biological entity works implies that it must be designed. By Behe's logic, more things were designed in the past than in the present.

Problem 5

Behe argues that irreducible complexity only takes place at the molecular level, not the organ level, yet ID makes arguments on the organism level.

Problem 6

Behe concedes that the theory of evolution proposes a mechanism for how things evolve: random mutations plus natural selection. He concedes that ID has NO mechanism, it merely “infers” design through a circular logic – whatever they can’t explain (argument from ignorance) must be “designed” See also the backwards logic in point 1 – which leads to the illusion of goal directed evolution.

Problem 7

Behe conceded that he had no way to infer how this designer worked (see 6). As per Behe’s own argument, there could be multiple designers. They could be natural. And there is no reason to presume that the designer still exists.

So, while IDers insist that design points to a supernatural 'entity' and that design can be inferred at the organ or organism level, none of these claims even follow from Behe's work. In fact, Behe himself concedes that descent with modification is a sound theory on the species level!

"Descent with modification gives him no problems, nor does natural selection. They are “trivial” and “modest” notions, respectively. Do his creationist fans know that Behe accepts as “trivial” the fact that we are African apes, cousins of monkeys, descended from fish?"

- Richard Dawkins, 'Inferior Design', Ny Times

"We now hear less about “irreducible complexity,” with good reason. In “Darwin’s Black Box,” Behe simply asserted without justification that particular biological structures (like the bacterial flagellum, the tiny propeller by which bacteria swim) needed all their parts to be in place before they would work, and therefore could not have evolved incrementally. This style of argument remains as unconvincing as when Darwin himself anticipated it. It commits the logical error of arguing by default. Two rival theories, A and B, are set up. Theory A explains loads of facts and is supported by mountains of evidence. Theory B has no supporting evidence, nor is any attempt made to find any. Now a single little fact is discovered, which A allegedly can’t explain. Without even asking whether B can explain it, the default conclusion is fallaciously drawn: B must be correct. Incidentally, further research usually reveals that A can explain the phenomenon after all: thus the biologist Kenneth R. Miller (a believing Christian who testified for the other side in the Dover trial) beautifully showed how the bacterial flagellar motor could evolve via known functional intermediates."

- Richard Dawkins, Ny Times

See also:

http://www.rationalresponders.com/blood_clotting_and_evolution_a_critique_of_one_of_behes_four_arguments_of_irreducible_complexity