Irreducible Incoherence – a look into the conceptual toolbox of a
(penultimate draft – to appear in Quarterly Review of Biology)
The concept of Irreducible Complexity (IC) has played a pivotal role in the resurgence of the
creationist movement during the past two decades. Evolutionary biologists and philosophers
have univocally rejected the purported demonstration of ‘intelligent design’ in nature, but there
have been several, apparently contradictory lines of criticism. We argue that this is in fact due to
Michael Behe’s own incoherent definition and use of IC. This paper offers an analysis of several
equivocations inherent in the concept and discusses the way advocates of the Intelligent Design
Creationism (IDC) theory have conveniently turned IC into a moving target. An analysis of these
rhetorical strategies helps us to understand why IC gained such prominence in the IDC
movement, and why, despite its complete lack of scientific merits, it has even convinced some
knowledgeable persons of the impending demise of evolutionary theory.
Irreducible Complexity; Evolutionary Biology; Pseudoscience; Conceptual Equivocations;
Intelligent Design Creationism
Until its dramatic legal defeat in the Kitzmiller vs. Dover case, Intelligent Design Creationism
(IDC) has been one of the most successful pseudosciences of the past two decades, at least when
measured in terms of cultural influence. It is instructive to have a look at the way this species of
creationism has achieved this success, notwithstanding its periodic strategic setbacks and
complete lack of scientific merits. Of course, a full explanation would include religious, socio-
political and historical reasons, but in this paper, we will have a closer look at the conceptual
toolbox and rhetorical strategies of the ID creationist. As a case study, we will here concentrate
on the central concept of ‘irreducible complexity’ (IC), but other examples can be found. Our
analysis shows that the conceptual equivocations inherent in the concept of IC, and in particular
its potential to function as a moving target in discussions (Boudry and Braeckman, 2010), may
help to understand the superficial appeal of the design argument based on IC, which is only the
most recent in a long series of creationist ‘challenges’ mounted against evolutionary theory.
In 1996, biochemist and ID proponent Michael Behe introduced the infamous concept of
irreducible complexity (IC) in his book Darwin’s black box. Although Behe’s critics univocally
agreed that he failed to demonstrate traces of ‘intelligent design’ in nature, there have been
several, apparently paradoxical lines of criticism. Some evolutionary scientists claim that
biological systems do sometimes exhibit IC as Behe defines it, but they deny that this poses a
problem for evolutionary theory (e.g. Orr, 1997; Shanks and Joplin, 1999; Miller, 2000). Others
maintain that Behe has never demonstrated the existence of bona fide instances of IC in nature
(e.g. Pigliucci, 2002; Forrest and Gross, 2007b). Pennock (1999:264-272) concurs with this
criticism but grants the possible existence of biological IC systems, arguing that these would not
threaten evolutionary theory in any case.
We propose that this seemingly contradictory criticism is in fact due to Behe’s own incoherent
definition and misleading use of IC. First, we introduce Behe’s concept and briefly rehearse the
most important empirical objections against the concept. Then, we analyse the conceptual
equivocations inherent in Behe’s approach on several levels (see also Dunkelberg, 2003). Finally,
we argue that these kinds of equivocations allow Behe and his IDC fellows to make a moving
target out of their theory, and hence to immunize it against criticism.
The evolution of irreducible complexity
The concept of IC has itself an interesting ‘evolutionary’ pedigree (Forrest and Gross, 2007a:302).
Already in the 1970s and 1980s young-Earth creationists used similar terms to describe biological
systems that were alleged obstacles to evolutionary theory. In 1974, Henry Morris, founder of the
Institute for Creation Research and father of the Creation-Science movement, argued in his
influential book Scientific Creationism that “the problem is simply whether a complex system, in
which many components function unitedly together, and in which each component is uniquely
necessary to be efficient functioning of the whole, could ever arise by random processes.”
(Morris, 1974:59) In 1980, young-earth creationist Ariel Roth argued that “creation and various
other views can be supported by the scientific data that reveal that the spontaneous origin of the
complex integrated biochemical systems of even the simplest organisms is, at best, a most improbable
event.” (Roth, 1980:83) [our italics] Behe has simply adapted these creationist notions to his own
ends. Consider his definition of IC in Darwin’s black box:
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
non-functional. An irreducibly complex biological system, if there is such a thing, would be a
powerful challenge to Darwinian evolution. (Behe, 2006:39)
Redundant and irreducible complexity
Behe then proceeds to argue that, especially at the subcellular level, many biological systems (e.g.
the bacterial flagellum) exhibit IC. Many critics have noted, however, that the components of a
typical biological system manifest considerable functional overlaps and redundancy. Contrary to
Behe’s assertions, living systems are often quite robust to perturbations, despite, or even because
of their complexity (Ciliberti et al., 2007). Overall the system exhibits what has been termed
“redundant complexity” (Shanks and Joplin, 1999). For example, if we eliminate one or even
several elements from the blood clotting cascade, which Behe thinks is an instance of an IC
system, the system still manages to perform its function, albeit not as swiftly or efficiently as
before. From the perspective of evolutionary theory this is hardly surprising: natural selection is a
clumsy and opportunistic process that tinkers with the available material. Thus, the widespread
phenomenon of redundant complexity makes it perfectly clear that evolution by natural selection
can gradually produce increasingly complex systems without the guidance of an intelligent
designer (see below).
Conceptual double life
To be sure, it is not difficult to find examples of biochemical systems in which the removal of
just one part damages the whole system. But consider Behe’s phrases “effectively ceases
functioning” and “by definition non-functional”. There are two possible reconstructions of his
definition: 1) the term “functioning” refers exclusively to the basic function currently performed
by the whole system (e.g. the rotary motion of the bacterial flagellum) and does not pertain to
other possible functions (in other contexts) when one or more components are removed; 2) the
phrase “effectively ceases functioning” includes any function the impaired system or one of its
components may perform in other contexts. In principle, it is not very hard to find out whether a
system exhibits IC in the first, weak sense. Leaving aside the ambiguity as to what are the natural
“parts” into which the system has to be decomposed (Dunkelberg, 2003; Sober, 2008:135-160), it
suffices to knock out these parts one after the other and see if the system can still perform its
basic function. But again, evolution by natural selection is perfectly capable of producing
complex functional systems exhibiting IC in the weak sense. For example, Lenski et al. (2003)
used a population of “digital organisms” (i.e. computer programs) to simulate the evolution of
complex functional system. By performing a series of knockout experiments on one of the
complex functions that emerged from their simulation, Lenski et al. were able to determine how
many genomic “instructions” were involved in its functioning. The researchers found that the
function “depends on many interacting components” (2003:141), the removal of any of which
causes the system to break down.
In fact, only an IC system in the second, strong sense could possibly pose a problem for
evolutionary theory, because it would rule out evolutionary precursor-systems and function-shifts
of the system’s components. However, it is hard to see how Behe could even begin to
demonstrate the existence of such a system without defaulting to the classical “argument from
ignorance” (Pigliucci, 2002:67). Interestingly, Behe has disingenuously exploited this very
ambiguity in answering his critics.
In his initial definition, Behe seems to intend the weak interpretation, but he then proceeds to use
the concept in a line of reasoning that only makes sense under the strong interpretation. Precisely
because the bacterial flagellum is IC, Behe tells us, it could not have evolved by means of random
mutation and natural selection. However, when critics object that the system’s components may
well be able to perform other functions in other contexts, or when they point to the possibility of
indirect evolutionary pathways, Behe switches back to the weak definition and blames his critics
for misrepresenting his argument.
A conceptual mousetrap
For example, Robert Pennock (1999:267) objected to Behe’s design argument that “even if a
system is irreducibly complex with respect to one defined basic function, this in no way implies
that nearby variations might not serve other nearby functions.” Reasonably, Pennock construes
Behe’s argument in a sense that is intended to preclude any functional intermediate on a direct or
indirect evolutionary path to the current system:
“Behe claims that there could never be any functional intermediates that natural selection
could have selected for on the way to any irreducibly complex system, but he can’t get the
empirical conclusion from his “by definition” conceptual argument.” (1999:267-268)
Pennock’s reasoning is correct of course, but in the afterword to the 10
anniversary edition of
Darwin’s Black Box, Behe (2006:258) retorts that “Pennock [simply] substituted his own concept
of irreducible complexity for mine”, whereupon he shifts back to the weak version of the
concept, which merely rules out direct improvements on the system: “On the contrary, on page
40, I point out that, although irreducible complexity does rule out direct routes, it does not
automatically rule out indirect ones.” (see also Ratzsch, 2005). Thus, Behe protests that Pennock
has “overlooked important qualifications” (Behe, 2001:707) and simply “constructed his own
rigid straw man definition for IC.” But Behe himself has boldly stated that any IC system is a
“powerful challenge to Darwinian evolution” (2006:39), and that “[w]e know of no other
mechanism, including Darwin’s, which produces such complexity.” (1996:25) Thus, the fact that
Behe’s own qualifications are inconsistent with his boastful presentation of IC as a major
stumbling block for evolution is hardly Pennock’s problem. Related to that point, Behe
acknowledged that Pennock exposed a weakness in the definition of IC, owing to its focus on
already-functioning systems rather than on the evolutionary development of such systems. Behe
promised to “repair this defect in future work” (Behe, 2001:695), but he has never lived up to
that promise, preferring to ignore the problem altogether.
However, the neglect of evolutionary development in Behe’s definition is hardly a trivial matter,
and his concession concerning indirect routes is quite an important one, which seems to be
completely absent from his original definition (see also Sober, 2008:161-162). Already in the
beginning of the 20
century geneticist Herman Muller explained how biological systems that
depend on the complex “interlocking” actions of many different components could come about
by evolutionary processes: “Many of the characters and factors which, when new, were originally
merely an asset finally became necessary because other necessary characters and factors had
subsequently become changed so as to be dependent on the former.” (Muller, 1918:463-464)
Thus, redundant complexity can eventually generate IC (under the weak interpretation). More
recently, biochemist and molecular biologist A.G. Cairns-Smith has formulated what is essentially
Behe’s notion of IC, and has proposed the analogy of “scaffolding” in the construction of an
arch to explain the evolution of IC systems (Cairns-Smith, 1986; see also Orr, 1997; Pennock,
2000). A classical stone arch is IC in the weak sense, because the structure will collapse as soon as
one removes either the keystone or one of the other stones. The support of scaffolding is
necessary in building a stone arch, but once the arch is completed, the scaffolding can be safely
removed. In a similar vein, a biochemical structure may have functioned as a scaffold in the
evolution of an IC system, before becoming dispensable and disappearing: “before the
multitudinous components of present biochemistry could come to lean together they had to lean
on something else” (Cairns-Smith, 1986:61).
Behe has repeated a similar conceptual sleight of hand in dealing with the objections of molecular
biologist Kenneth Miller (2000). Miller accepts that some biological systems are IC as Behe
defines it (weak version), but he objects to the anti-evolutionist conclusions Behe derives from
IC. As a counterexample of Behe’s claim, Miller offers a plausible reconstruction of the
evolutionary history of the five-part auditory apparatus in mammals, which he argues fulfils the
definition of IC. Miller demonstrates that the individual parts of the auditory apparatus – mallens,
incus and stapes – evolved from the rear portion of the reptilian rear jaw. Importantly, before
they migrated to the middle ear and were adapted for their new purposes, these structures were
perfectly functional indeed. Thus, Miller concludes that Behe’s statement (2006:39) to the effect
that “any precursor to an irreducibly complex system that is missing a part is by definition non-
functional” is plainly wrong. Reasonably, Miller (2000:139) now challenges strong IC and
demonstrates the crucial point, which is that the “interlocking necessity [of the parts of the final
working system] does not mean that the system could not have evolved from a simpler version.”
Behe (2006:259) however has responded that Miller “concocted his own, private definition of
irreducible complexity, and then argued against that.” It is quite possible, writes Behe, that
individual components of an IC system can perform functions in different contexts. Thus,
according to Behe (2006:260), Miller has “redefined irreducible complexity to mean that none of
the component parts of an IC system could have its own function separate from the system.”
But again, the equivocation is in Behe’s definition, not in Miller’s criticism. Bearing in mind that
Behe treats IC as if it were an insurmountable obstacle for evolution – which is already clear from
the very wording of the term “irreducible” – the critic naturally confronts Behe’s claim of “non-
functionality” by pointing to the different functions performed by evolutionary precursors of IC
systems, which may or may not have contained parts of the current system.
After all, if we bear in mind that biological systems can be exapted over the course of evolution
for another function than that for which they were originally selected, for instance by being
integrated as part of a new system performing a different function, then Behe’s non-functionality
claim becomes either trivial (weak version) or plainly wrong (strong version).
Dembski’s conceptual remedy
In No Free Lunch (2002) Behe’s creationist ally William Dembski proposed to remedy the
conceptual problems of IC. He thinks that the concept of IC is “salvageable” (2002:280), and
after a series of modifications, arrives at the following new definition:
– A system performing a given basic function is irreducibly complex if it
includes a set of well-matched, mutually interacting parts such that each part in the set is
indispensable to maintaining the system’s basic, and therefore original, function [our emphasis]. The
set of these indispensable parts is known as the irreducible core of the system. (Dembski,
Accordingly, Dembski argues (1999:148), the IC of a system is a straightforward empirical
Individually knocking out each protein constituting a biochemical system will determine
whether function is lost. If it is, we are dealing with an irreducibly complex system.
Clearly, Dembski has “fine-tuned” the concept of IC in the direction of the weak interpretation,
restricting the definition to the basic, original function of the system. His updated version has the
merit of conceptual clarity (but see Perakh, 2002), but in remedying Behe’s conceptual ambiguity,
Dembski actually takes the sting out of the whole argument. If IC thus conceived is consistent
with indirect and circuitous routes, scaffolding and exaptations, what is all the fuss about? The
collapse of IC in Dembski’s hands illustrates that the conceptual ambiguity he was trying to
salvage was actually very convenient for Behe.
Even after Demski’s treatment, the equivocations in the concept of IC are not yet resolved.
Having failed to provide an objective criterion that makes evolutionary accounts impossible, the
IDC proponent retreats to a weaker probabilistic claim: as the number of individual components
in an IC system increases, the plausibility of a gradual succession of slight modifications becomes
vanishingly small: “the strength of the inference depends on the number of parts, and the more
intricate and sophisticated the function, the stronger is our conclusion of design.” (Behe,
2006:265) Leaving aside the problems with this alleged correlation between the numbers of parts
and the strength of the design inference, which were amply documented by Pennock (1999:270),
we still seem to be left with a testable statement. If we can find a well-functioning precursor for
one of the systems discussed by Behe (or one of its components), or if we can construct a
plausible evolutionary pathway for one of Behe’s examples, the ‘probability’ argument collapses.
Behe’s claim has indeed been tested against the facts and found wanting (Miller, 2000; Lenski et
al., 2003; Young and Edis, 2006; Forrest and Gross, 2007a). In response to these demonstrations,
however, IDC proponents belatedly ‘reinterpret’ their initial claims in order to lift them out of
the critic’s reach. A first strategy to this end consists in shifting the burden of proof from plausible
evolutionary pathways to the actual evolutionary story, maintaining that the broad outlines of a
plausible evolutionary account amounts to nothing more than Darwinian wishful thinking and
speculation. The same bait-and-switch technique can be discerned here: IC is constantly boasted
as a point of principle for ruling out the possibility of evolutionary explanations, but as soon as it is
challenged on that ground, through a discussion of plausible evolutionary scenarios, ID
creationists pretend that they were talking about actual evolutionary pathways all along.
When they are confronted with tangible evidence of actual evolutionary history, IDC theorists
resort to a second strategy, shifting their design claims to the remaining parts of the evolutionary
puzzle, as if the ‘real’ problem was always there. For example, Kenneth Miller (2004) beautifully
demonstrated the structural similarities between one component of the flagellum and the so-
called type III-secretory system. He convincingly argued that the former is a very plausible
evolutionary precursor of the latter, which has been co-opted by evolution to perform a new
function. In response to this embarrassing demonstration, Behe (2001:689-690) simply shifted his
attention to the complexity of the newly discovered system by itself, and at the same time
stubbornly insisted that the assemblage of these precursors into the flagellum system is still
impossible without the helping hand of a Designer (Behe, 2004:359).
In light of these evasions, the question arises if there is any amount of comparative genetic
evidence, or any level of evolutionary reconstruction, that would make Behe and his allies
abandon their design claims. Because of the sloppiness of the probabilistic IC claim (which is
never based on any serious quantification of probabilities), IDC theorists can continue to raise
the evidential requirements up to a point where the concept of IC is lifted outside of the
empirical domain altogether. Indeed, when pressed on the available knowledge on the IC systems
he uses, Behe has made it clear that only a complete, quantitative, fully detailed description of
what actually happened over the course of evolution would convince him (Behe, 2007). In his
testimony at the Dover trial, Behe conceded:
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. (2005:19)
But this is an absurd demand, which is never met in any other scientific domain, and it is certainly
not met by ID creationists themselves when they propose ‘design’ as an alternative explanation.
Indeed, despite his demand for such a high level of evidence for the evolution of what he claims
are IC systems, Behe himself has been completely unwilling to flesh out his design hypothesis to
any degree at all, insisting that the motives and character of the designer are in fact inscrutable,
and providing us with no clue as to his modus operandi. As for Behe’s request for fully detailed
knowledge about evolutionary history, Pigliucci (2002:240) has warned biologists not to be
overconfident in taking up creationist challenges, and not to mistake partial reconstructions and
plausible scenarios for a complete understanding of evolutionary development. Indeed,
evolutionary theorists are better advised to explain why the burden of proof insisted on by
creationists is absurd, and to point out that scientific knowledge will never be complete in this
In any case, what is disingenuous in Behe’s presentation is that this challenge to offer a complete
and step-by-step evolutionary account of IC systems is not spelled out from the beginning, but is
a belated revision of his original claim (based on ambiguities in his definition). In Darwin’s black box,
Behe leaves us with the impression that the concept of IC is in principle easy to challenge, but
when his critics actually set out to do so, as we saw in the discussion with Pennock and Miller,
Behe dodges and weaves like a hunted rabbit. Thus, what remains of Behe’s argument boils down
to the same old “argument from personal incredulity” (Dawkins, 1991:38), which is a far cry from
the ‘objective criterion’ for design IDC theorists had promised.
It is interesting to note that the same pattern of reasoning has always been rampant in traditional
creationist arguments about the so-called ‘gaps’ in the fossil record. Creationists claim that they
could be easily convinced of evolution if only the ‘missing links’ between the taxonomic groups
turned up in the fossil record. But whenever such a fossil is found, they complain that the
intermediate is not really the ancestor of the present organism (an impossible requirement for
fossils), or even that Darwinists now face an ever bigger hurdle, because they are left with two
gaps to explain. The latter principle has been coined “Gish’s law” by geologist Robert S. Dietz
(1983), after young-earth creationist Duane Gish.
Falsification and Non-instantiation
Of course, the design argument based on IC always allows for a final retreat. Suppose we can
provide IDC proponents with a fully detailed description of the evolution of the bacterial
flagellum. Even if the stubborn insistence on the flagellum’s exhibiting IC would at that point
become absurd even in the eyes of ID creationists themselves (although one can never be too
sure about that), they would not have to regard this as a refutation of IDC as such, but merely as a
specific case in which their design claim was not instantiated. The expectation that this particular
biological system would exhibit IC and hence be one of those unmistakable traces of design
would simply be disappointed, and the search for new obstacles to evolution can begin.
In fact, this is what the history of the creationist movement is all about: if the case for evolution
by natural selection becomes too overwhelming, creationists typically drop their favourite
examples of complexity and come up with fresh ones, whose evolutionary origins are still
relatively obscure (Pennock, 1999:171-172). For example, the traditional objection against
evolution used to be the vertebrate eye. Nowadays, the evolutionary development of the
vertebrate eye is well understood and it has become an outdated argument against evolutionary
theory. It is not even a particularly difficult example for evolutionary theory, because it involves
relatively straightforward selection pressures.
As the evolutionary history of the bacterial flagellum and the blood clotting system are being
unravelled, the next generation of creationists can always disclaim the examples of their IDC
forebears, and a new round of pointless arguments can begin (though they would at least have to
admit that their former ‘design criterion’ was defective because it generated false positives).
However, the retreat into unknown territory cannot go on indefinitely. In fact, as Robert
Pennock (1999:171) remarked, the current preoccupation of IDC theorists with invisible
biochemical niceties like the propeller system of the E. Coli bacteria indicates “just how far
creationists have had to retreat to find significant explanatory gaps in evolutionary theory.”
Moving the goalposts
The most conspicuous feature of the concept of IC is not so much its ambiguity, but the
discrepancy between what it seems to promise and what it eventually delivers, as far as testable
empirical claims are concerned. On first reading Behe’s argument, the unsuspecting reader may
get the impression that Behe really sticks his neck out and presents evolutionists with a clear
empirical challenge. However, this apparent rigour of the IC concept as an objective criterion of
design, which arguably makes it appealing to anti-evolutionists, evaporates upon closer inspection.
Under the weak interpretation, the concept describes a well-known phenomenon in the living
world that is unproblematic for evolutionary theory. Under the strong interpretation, IC systems
would indeed confront evolutionary theory with serious problems, but Behe has not given us an
inkling of how we could ever demonstrate whether a system qualifies as IC in this sense. Indeed,
it would require ruling out any conceivable evolutionary history, and thus amount to showing that
no part or precursor of the system in question is able to perform any other function, in any
situation and at any time.
This allows for an interesting bait-and-switch strategy, which one could describe as follows: ‘First
present evidence for weak IC in the living world, then pretend that strong IC has been
demonstrated and continue to equate IC with “unevolvability”. If challenged on empirical
grounds, jump back to the weak version and accuse your critics of misrepresenting your
argument. Switch the IC claim to subsystems and assembly of components, keep raising the
standards of evidence, and reassert that all this directly follows from the simple objective
criterion of IC. Finally, when really pressed against the wall, give up this particular system and
quickly find a new one. Repeat the circle ad libitum.’
Behe’s concept of IC is not the only instance of conceptual equivocation in the IDC literature.
Two examples may be the subject of further research. First, when writing about ‘information’,
William Dembski surreptitiously switches between its standard interpretation in information
theory, in which it is a measure of the randomness in a system, and its colloquial use in the sense
of ‘meaningful message’ (Perakh, 2004:64-75). This ambiguity allows him to give the false
impression that the ‘information’ encoded in for example DNA points in the direction of an
A second example is the IDC response to the series of mousetraps which John McDonald
devised to refute the claim that gradualist evolution of IC systems (with the mechanical
mousetrap as a paradigm example) is impossible. Having thus been confronted with their lack of
imagination, IDC theorists now complain about the manifest need for intelligent guidance in
constructing these series of mousetraps (Behe, 2004:364-366). Amazingly, they argue that
McDonald’s mousetraps in fact demonstrate that an IC system always requires an Intelligent
Designer. But this reply illegitimately shifts the discussion – which is in fact about a human artefact
and thus in any case irrelevant – from the IC of a mousetrap to the blind and unguided character of
Although the Kitzmiller vs. Dover has damaged the IDC movement in terms of credibility, it
does not show real signs of disappearing. As Forrest and Gross note in an afterword to their
meticulous study of IDC’s politics and religious ideology, the movement has simply changed its
strategy once again. After the recent legal setbacks they have been forced to drop overt talk of
“intelligent design” and adopt code words like “academic freedom” and teaching “the strengths
and weaknesses of evolution” instead. (Forrest and Gross, 2007b:337) “[C]reationists never give
up. They merely change their strategy with each new defeat.” (Forrest and Gross, 2007a:309)
As was transparent from its conception, the rapid success of the IDC movement was never
driven by its arguments but by its religious ideology, which was epitomized in the so-called
Wedge document of IDC’s home basis the Discovery Institute (Forrest and Gross, 2007b).
Beyond religious motivation, one can point to sociological, cultural and political factors to
account for the remarkable success of IDC (outside the scientific community, to be sure), and it
is plausible that the persistence of anti-evolutionary sentiments and the continuing appeal of the
design argument is also a function of deeply rooted cognitive dispositions and hard-to-shake
teleological intuitions about the world (Kelemen, 2004; Kelemen and Rosset, 2009).
However, anti-evolutionism can take many different forms, and not all of them can achieve equal
cultural success. In this paper we have analyzed some of the rhetorical strategies which Behe and
other IDC theorists have used for presenting their challenge to evolution and for deflecting valid
criticism. On the one hand, we claim that Behe’s presentation of IC has the appearance of an
objective design criterion, which makes it superficially more respectable than the age-old
“argument from personal incredulity”. On the other hand, the equivocations that are built in the
definition of IC allow it to be used as a constantly moving target (Boudry and Braeckman, 2010),
as a kind of conceptual chimera that is hard to pin down by critics. These considerations partly
explain why the concept of IC was hailed by the movement as the ultimate challenge to
evolutionary theory, and why, despite its complete lack of scientific merits, it has convinced even
some knowledgeable persons of the impending demise of evolutionary theory. As Robert
Pennock (1999:1) wrote:
We think of creationism as a cluster of ideas that reproduces itself by spreading from mind to
mind and struggling with competing ideas for a home among a person’s beliefs. Sometimes it
loses out to more powerful rival ideas, but sometimes it finds receptive mental soil, takes root
and waits to be passed on again.
Indeed, in the past two decades the concept of IC seems to have found receptive mental soil
among anti-evolutionists. An analysis of the convenient conceptual equivocations inherent in IC,
and the rhetorical strategies with which it was presented, helps us to understand this remarkable
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