Beyond suboptimality

Why irreducible complexity does not imply intelligent design

Mark Perakh

Michael Behe's book Darwin's Black Box is one of the most popular and extensively reviewed books promoting intelligent design "theory." The concept of "irreducible complexity" propagandized in that book has been touted by Behe and other intelligent design advocates as a great discovery and used as one of the main tools in their efforts to "destroy Darwinism" (the goal openly announced by such "leading lights" of intelligent design as Phillip Johnson [1991] and Jonathan Wells [2002]).

Irreducible complexity, according to "design theorists," implies intelligent design of biological system. In fact, such a conclusion lacks a logical foundation. Irreducible complexity even can more reasonably be construed as an argument against intelligent design.

Michael Behe's concept of irreducible complexity (IC) (Behe 1996) has been critically discussed by experts in biology  -- see, for example, publications by H. Allen Orr (1997), Russell F. Doolittle (1997), David Ussery (1999, 2004), Kenneth R. Miller (1999), Gert Korthof (1999), Matt Inlay (2002), Pete Dunkelberg (2003), and others. The attitude of many professional biologists to Behe's IC concept has even found its most uncompromising expression in Kenneth Miller's words: "... the notion of irreducible complexity is nonsense." (1999, p. 150).

While the critical analysis of the IC concept by professional biologists seems to be sufficient to dismiss Behe's alleged great discovery in biology, there is another aspect to IC which, to my mind, makes the very notion of "IC implies intelligent design (ID)" implausible.

A concept identical in all but name to Behe's irreducible complexity was around for a long time before Behe. It was applied to the problems of evolution of various anatomical structures, such as the mammalian eye (recall the many times answered question, "what good is half an eye?"), or the snakes' apparatus of venom injection (Marcell 1976), etc.

Even more relevant, a practically identical concept ("interlocking complexity") was discussed from the standpoint of genetics already nearly 80 years earlier (Muller 1918, 1939). Even the application of the IC concept to the molecular assemblies within a biological cell (which is Behe's playing field) was put into circulation some ten years before Behe (Cairns-Smith 1986). Unlike Behe and his supporters, these Behe's predecessors did not claim that the concept in question constitutes a great discovery or implies intelligent design, so in the rendition of these predecessors it would hardly invoke Miller's categorical rejection quoted above.

The critical discussion of Behe's ideas has mainly concentrated on three aspects of IC, to wit:


  1. The first aspect of IC subjected to discussion has been about the very definition of IC. To my knowledge, Behe himself has never acknowledged that his definition was in any way imperfect. However, Behe's colleague William Dembski (viewed by the ID advocates as their leading logician) admitted that Behe's idea of IC was "neither exactly correct nor wrong" (Dembski 2002, p. 280).

  2. The second aspect of IC subjected to critique was the question of whether molecular systems offered by Behe as examples of IC are indeed IC. A number of biologists pointed out that systems such as bacterial cilia or blood-clotting cascade which, according to Behe, exemplify IC, are in fact reducible without losing their "basic function." (See, for example, Miller 1999).

  3. The third aspect of IC subjected to critique is the most important. Behe asserts that IC systems (exemplified by the protein assemblies in biological cells) cannot have evolved via a direct "Darwinian" path because such a path necessarily goes through a sequence of intermediates each performing the same "basic" function. Since any system comprising fewer parts than the IC system in question is, by definition of IC, dysfunctional, it could not be an evolutionary precursor of an IC system, or so says Behe.  Regarding evolution of IC system via an indirect evolutionary path, Behe admits that such a process is possible but, in his opinion, so highly improbable that it cannot be considered a feasible option.

The last point has been disputed by professional biologists. They suggested detailed scenarios showing how, for example, a bacterial flagellum could have evolved from evolutionary precursors with a sufficiently high likelihood (Matzke 2003, Ussery 2004, Musgrave 2004).

The consensus of the majority of professional biologists seems to favor the views of Behe's opponents.  Except for vague protestations wherein Behe and his supporters demand from their opponents highly detailed proofs of the factual occurrence of indirect evolutionary paths leading to IC systems, Behe seems to be unable to offer substantive counter-arguments.

In this essay I will analyze the IC concept from a viewpoint different from the three aspects of the problem listed above. I intend to show that even if the IC concept is valid, and even if many biological systems are indeed IC, this in itself does not logically lead to design inference. My contention is that IC in itself can more reasonably be construed as an argument against design inference.

In an essay titled "Irreducible Contradiction" posted to the internet in 1999 (see reference) I suggested critical comments to Behe's Darwin's Black Box. This essay was translated and printed in Russia (Perakh 2001a) and in Israel (Perakh 2001b).  After its appearance in Russian in Kontinent the essay was reproduced on several Russian websites and invoked a discussion which sporadically continues even now (February 2005). By the end of 2003 my book Unintelligent Design was published wherein chapter 2 was essentially a slightly modified version of the same essay (Perakh 2004).  Recently that chapter was translated into Polish and appeared in the Polish journal Filozoficzne Aspekty Genezy (Philosophical Aspects of Origin) -- see .

In the nearly six years since the appearance on the internet of the essay in question, Michael Behe has never uttered a word acknowledging the existence of my critical remarks.  Nor has William Dembski, who has actively promoted Behe's irreducible complexity concept, ever mentioned my critical comments. Neither did anybody else from the intelligent design camp.

Recently Dembski posted an article titled "Irreducible Complexity Revisited," (Dembski 2005) which has initiated some discussion (RBH 2005, Perakh 2005). An article by Behe appeared recently in New York Times, wherein Behe repeats again the same much critiqued notions without having changed his position or having accounted for a single point suggested by his critics. I think therefore it is worthwhile to revisit certain points which seem to be in need of clarification, regarding the IC concept and its alleged logical segueing into ID.

I'll not discuss here Dembski's recent modifications of the IC definition (addressed in Perakh 2005 and RBH 2005).  Instead, I will refer to Behe's original definition of IC, which, albeit suffering from certain deficiencies (as admitted by Dembski 2002), does essentially reflect his principal idea.

The essence of Behe's original IC concept is as follows:

A system is IC if:

(a) It consists of several parts.

(b) The parts are "well matched." (Behe offered no definition of the notion of being "well-matched.")

(c) It performs a certain "basic" function (for example, clots blood);

(d) It ceases to function if even a single part is missing.

Having discussed several examples of protein "machines" in biological cells, which, according to Behe, are IC, Behe then asserts that the existence of IC systems in a biological cell points to them being designed rather than having emerged as a result of evolution. I intend to show that Behe's assertion contradicts logic.

Note that Behe's concept of IC comprises two components: one is complexity and the other is irreducibility.

Behe expends a lot of effort to demonstrate how staggeringly complex the protein systems in a cell are.  It is evident that for Behe the complexity in question is part of his idea, pointing to design as the alternative to evolution. According to Behe, biological systems must have been designed because they (A) are very complex; and (B) cannot function unless all of their parts are present.

Regarding (A) -- complexity -- note that Behe has not provided a definition of complexity. Several such definitions have been suggested, though, by Dembski.

As has been pointed out before (Perakh 2004), Dembski's various definitions of complexity are often incompatible with each other.  There is among them, though, a definition repeated by Dembski many times, which is in tune with Behe's point (A). According to that definition complexity is equivalent to small probability (Dembski 1998). For example, Dembski asserts in his book that "probability measures are disguised complexity measures" (page 114). Variations of this assertion are scattered over Dembski's books. Thus the more complex a system, the less probable its spontaneous emergence as a result of chance, or so says Dembski. So, according to Behe and Dembski, the more complex a system, the more likely it was designed -- this is the essence of point (A) in Behe's concept.          

Point (B) -- irreducibility -- in Behe's concept asserts that an IC system loses its function if even a single part is missing. 

According to Behe, protein "machines" in a cell meet both requirements for being IC -- they are very complex and they are irreducible. 

My goal now is to discuss: what if this assertion is true? Does it lead logically to the design inference?  Behe's answer to this question is "Yes."

I submit that Behe's answer is illogical. Here is why.

Start with complexity.

As I have argued before (Perakh 2004), contrary to Dembski's persistent assertions, complexity is certainly not just disguised improbability. Examples to the contrary abound. Imagine a pile of stones. Each stone has some irregular shape that resulted from a series of chance events. Among these irregularly shaped stones we find a perfectly rectangular brick.  It has a simple shape which can be described by a short (i.e. simple) program containing only three numbers -- width, length, and height. On the other hand each of the irregularly shaped stones can be described only by a more complex program containing many numbers.  However, the probability of a rectangular brick being a result of chance is low: the brick is reasonably (with a high probability) assumed to be a product of design. For irregularly shaped stones the opposite is true -- the probability of their origin in chance is larger than in design. Here the relationship between probability and complexity is opposite that prescribed by Dembski's definition (but compatible with the definition of Kolmogorov complexity -- see, for example, Chaitin 2003).

In this example simplicity rather than complexity is a marker of design. I submit that the described example shows not only that Dembski's definition of complexity fails for certain situations but also that, generally, a more reasonable statement is that simplicity points to design while complexity as such points to chance (more about this in Perakh 2004).

If this is so, then the first part of Behe's IC concept -- complexity - is more reasonably construed as an indication of "blind" evolution rather than of design.

Now turn to the second part of Behe's IC -- irreducibility. Recall that Behe's idea is that losing a single part of a protein "machine" makes it non-operational. Therefore, says Behe, such a "machine" could not have evolved via a "Darwinian" evolutionary process which requires the existence of functional precursors.

The simple fact is, though, that if an IC system has been designed, we have a case of a bad design.  If the loss of a single part destroys the system's function, such a system is unreliable and therefore, if it is designed, the designer is inept. When engineers design machines, bridges, skyscrapers, TV sets, or artificial kidneys, they always try to envision what can go wrong with their design and how to ensure that small defects do not result in a failure of their product; to this end they build in certain redundancies so that in case some part of the construction fails, its function will not be completely lost but rather taken over by certain self-compensatory features.

IC systems, by definition, are highly vulnerable to accidental damage.

IC systems, if they are designed, are poorly designed.

It must be stressed that in this case we go beyond the problem of suboptimal design. When we deal just with suboptimal design as such, the ID advocates suggest various arguments supposedly justifying the reasons for design being not optimal. For example, one such argument is that we simply don't know anything about the designer's reasons to behave as he does; hence our notion is just an argument from ignorance; perhaps whatever from human limited standpoint looks like suboptimal design has good reasons beyond our comprehension to be as it is, etc.  Such an argument usually (albeit not always explicitly) presumes that suboptimality is a "side effect" rather than a deliberately chosen goal of the designer.

Whether such arguments are convincing depends on the mindset of the particular persons.  For this discourse, however, such an argument is not really relevant. Indeed, Behe's concept contains as a crucial part the assumption that the irreducibility of biological system is a marker of design.  Such an assumption is obviously not about a designer who has failed to provide an optimal solution or compromised in his design for some unknown reason. It is no longer about some "side effect" which the designer has simply failed to correct or has kept for unknown reasons, extraneous to the design's purpose.  

Behe's concept assumes that the very feature which makes the design bad means the system has been designed. In other words, Behe's concept means that suboptimality is  viewed not as just an unfortunate oversight by the designer; nor is it viewed as something that, albeit seemingly detrimental for the designed entity, has some reasons known only to the designer but unfathomable to us. No, in Behe's concept the very suboptimality is suggested as a marker of design: an IC system by definition is easily destroyed by damaging just a single part, so a system's being IC means that its vulnerability is its ineliminable feature.  Behe's idea implies that the system is IC (and hence suboptimal) because such was the goal of the designer.  "The system is suboptimal, therefore it is a product of design" -- that is what Behe's concept entails.

ID advocates are welcome to accuse me of offering a caricature of their idea, but it cannot be helped when a concept's essence sounds like a caricature or a parody; the idea that "IC implies ID" can most succinctly be rendered by a maxim: stupid, therefore designed.

If this is a satisfying logic, I don't know what a lack of logic is.

Remember also that Behe's design inference is based not on some positive evidence but rather on a negative assertion:  IC systems could not have evolved via a "Darwinian" path. Since such a path is impossible, concludes Behe, the only remaining option is design.

This is an argument of the "either-or" type.  I will not discuss here whether or not there indeed are only two mutually-exclusive options. My point is different: if Behe infers design only because the direct evolutionary path, in his view, is impossible and an indirect evolutionary path is improbable, then, to be consistent, he should use the same probabilistic criteria for judging whether or not it is reasonable to assume that the feature which makes design bad is a marker of design.  How probable is it that the putative designer deliberately designs his products to be IC if this means the product will be unreliable?

Dembski asserts that ID does not imply a smart designer (Dembski 2001). Designer can even be stupid, says Dembski.  However, from many other utterances of ID advocates, including Dembski, it is clear that all such statements are just a smoke screen and in fact they believe that their "designer" is the God of the Bible. (See, for example, Dembski 1999, part 3, or Johnson 2000.) This designer is supposed to be omnipotent and omni-benevolent.

In fact, ID advocates want to have their cake and to eat it too. On the one hand they concede that the putative designer may even be stupid -- this they say when trying to explain suboptimality of design.  On the other hand they speak about Christian values, cultural war, the Logos of John's gospel and the imminent triumph of ID over "materialistic" science. (Dembski 1999, part 3; Johnson 2000). It is not by accident that the leading young earth creationist, Henry Morris, who is more consistent in his frank biblical literalism, referred to Dembski's contortions regarding the nature of the designer as "nonsense." (Morris 2005).

How probable is that the very features that make design bad are markers of design (as follows from Behe's discourse)? It is hardly less improbable than the evolution of protein assemblies via indirect "Darwinian" paths.

If Behe infers design just because evolution of protein assemblies via indirect "Darwinian" paths looks improbable to him, design inference also has to be excluded because of the improbability of the putative designer's deliberately incorporating in the protein assemblies the very features (like IC) which make the design bad.

The above discourse is, to my mind, sufficient to reject the design inference based on the IC concept, as logically untenable.


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Mark Perakh is a retired professor  from Cal. State University with the Emeritus status. He is a prominent skeptic who is passionately engaged in debunking various kinds of crank science. Author of Unintelligent Design.