- Introduction
- The Argument From Irreducible Complexity
- Co-option
- Causal Adequacy
- The Connection With Specified Complexity
- Conclusion
- Notes
Intelligent Design advocates claim that an intelligent designer
was involved in the origin of certain biological structures, and
that this conclusion is justified by a scientific inference
from empirical evidence. The main arguments which they offer in
support of these claims are those of Michael Behe and William
Dembski. Those arguments have appeared in a number of popular books
and articles, though never in a formal technical paper, and have
been widely criticized by biologists and others. The criticisms
have been many and varied, but the
primary one has been that, once shorn of error and
obfuscation, all that's left is the age-old
god-of-the-gaps argument, also known as the argument
from ignorance. This argument is based on the undeniable
premise that scientists have not fully explained certain observed
phenomena, and insists that those phenonema therefore
cannot have a natural explanation and so must be the work
of God. ID advocates replace the word "God" with "a designer"
(who they nevertheless believe to be God), but the basic form of
the argument is otherwise unchanged.
Since the god-of-the-gaps argument has long been rejected by
scientists and philosophers of science, and ID advocates realize
how weak the argument appears, they insist they have a
stronger argument. They claim they can demonstrate that the
probability of biological structures evolving by natural
selection is so small as to make it effectively impossible for such
evolution to occur. Even if this claim were justified, they would
still be relying on a god-of-the gaps argument, though a somewhat
stronger one: these structures cannot have evolved by natural
selection and biologists do not have another explanation; therefore
they must have been designed. However, their position is actually
far worse than this, because their probabilistic claim is
unsupported by any substantive argument. When pressed to justify
the claim, they merely fall back on another argument from
ignorance: biologists have not given a fully detailed account of
how the structures evolved. To conceal the emptiness of their
arguments, ID advocates confuse their readers by the use
of idiosyncratic and ill-defined terms, equivocal claims,
misleading rhetoric, and--in Dembski's case--irrelevant
mathematical notation.
This article will not discuss the merits of the god-of-the gaps
argument. My purpose is merely to demonstrate that the
arguments of ID advocates take this form. If they wish to attempt a
justification of the god-of-the gaps argument, ID advocates are
welcome to try. What is far less welcome, however, is their attempt
to represent the argument as something more impressive, by hiding
it behind a smokescreen of pseudoscientific mumbo jumbo.
Dembski's fullest exposition of his argument for intelligent
design occurs in his book No Free Lunch [1]. Although he
dresses it up in misleading discussions of probablity, complexity,
information and specification, the core of Dembski's case is the
argument from irreducible complexity. It is essentially the same
argument made by Behe in his book Darwin's Black Box [2].
I have previously criticized No Free
Lunch in detail [3], but, despite writing two lengthy
responses to my critique [4, 5], Dembski has entirely evaded addressing
the substance of my arguments.
Since the publication of No Free Lunch , Dembski has
written a number of articles in which his argument appears to have
changed significantly. He has apparently abandoned a key part
of his argument, though he never clearly acknowledges this.
Here I will address his argument as he presents it in his most
recent article, Irreducible Complexity Revisited [6]. [Just
before the current article was finalized, Dembski published a new
book, The Design Revolution. I have not yet seen that book, so cannot comment on any additional or altered arguments it might contain.]
Dembski 's latest definition of
irreducible complexity is as follows:
A functional system is irreducibly
complex if it contains a multipart subsystem (i.e., a set
of two or more interrelated parts) that cannot be simplified
without destroying the system's basic function. I refer to
this multipart subsystem as the system's irreducible core.
As with previous attempts by Behe and
Dembski to define irreducible complexity, this definition is vague
and ambiguous in a number of respects. What constitutes a "part"?
In his sole example (the flagellum of the bacterium E.
coli), Dembski takes the parts to be proteins. But can a
collection of proteins constitute a part? What about a piece of a
protein? Also, what does it mean for a subsystem to be "simplified
without destroying the system's basic function"? Is simplification
limited to the removal of existing parts (as in Behe's original
definition), or can it include the replacement of a part with
a modified version? Can it include the replacement of the
whole subsystem with a simpler subsystem operating on a quite
different principle?
Though Dembski gives only one example, he
seems to assume that other irreducibly complex systems exist. It
would be a mistake, however, to assume that the systems claimed as
irreducibly complex by Behe are also irreducibly complex in
Dembski's sense, since their definitions differ
significantly. Without further clarification of Dembski's
definition, it is impossible even to confirm that the bacterial
flagellum is irreducibly complex in his sense.
Fortunately, these questions need not
concern us too deeply, since the concept of irreducible complexity
turns out to be nothing but a red herring. Dembski argues that
an irreducibly complex system cannot evolve by "a direct Darwinian
pathway", which he defines as follows:
A direct Darwinian pathway is one
in which a system evolves by natural selection incrementally
enhancing a given function. As the system evolves, the function
does not evolve but stays put.
Let us assume for the sake of argument
that Dembski's conclusion is valid, and that the bacterial
flagellum could not plausibly have evolved by a
direct Darwinian pathway. Why should we care? Dembski's
concept of direct Darwinian pathways is a straw man, an
absurdly oversimplistic idea of evolution. In practice,
biological systems are not restricted to maintaining the same
function as they evolve. Their function can and does
change. A system which has evolved for one use can
be co-opted for another use. Co-option is
discussed further in the following section.
Clearly, having divided evolutionary processes into direct and
indirect pathways, Dembski must make a convincing case against both
possibilities if his overall case is to stand. So what is his
argument against evolution by indirect pathways? Why, it's our old
friend the argument from ignorance: biologists have not given fully
detailed accounts of such pathways, so we must reject the
possibility that they exist. To show that I am not
misinterpreting him or omitting anything vital, I present his
argument in full:
How does the argument from
irreducible complexity handle indirect Darwinian pathways? Here the
point at issue is no longer logical but empirical. The fact is that
for irreducibly complex biochemical systems, no indirect Darwinian
pathways are known. At best biologists have been able to isolate
subsystems of such systems that
perform other functions. But any reasonably complicated machine
always includes subsystems that perform functions distinct from the
original machine. So the mere occurrence or identification of
subsystems that could perform some function on their own is no
evidence for an indirect Darwinian pathway leading to the system.
What's needed is a seamless Darwinian account that's
both detailed and testable of how subsystems undergoing coevolution
could gradually transform into an irreducibly complex system. No
such accounts are available or forthcoming.
Indeed, if such accounts were available, critics of intelligent
design would merely need to cite them, and intelligent design would
be refuted.
In making an argument from ignorance, it serves Dembski's purpose to
exaggerate the ignorance of biologists. They may not have provided the
exhaustively detailed ("seamless") account which he demands, but they have
proposed outline accounts for several of the systems which Behe claims are
irreducibly complex.
As he has done in many previous articles, Dembski denies that he
is making an argument from ignorance. But the denials are never
substantiated. Instead, each one is followed by yet
another argument from ignorance. All that changes is the wording.
Here's another example:
If after repeated attempts
looking in all the most promising places you don't find what
you expect to find and if you never had any evidence that
the thing you were looking for existed
in the first place, then you have reason to think that the thing
you are looking for doesn't exist at all. That's the
argument from irreducible complexity's point about indirect
Darwinian pathways. It's not just that we don't know of
such a pathway for, say, the bacterial flagellum (the irreducibly
complex biochemical machine that has become the mascot of the
intelligent design community). It's that we don't know
of such pathways for any such systems. The absence here is
pervasive and systemic. That's why critics of Darwinism like
Franklin Harold and James Shapiro (neither of whom is an
intelligent design proponent) argue that positing as-yet
undiscovered indirect Darwinian pathways for such systems
constitute 'wishful speculations.'
Even if all its premises were justified, the above argument
would remain an argument from ignorance. But the argument is
even worse, in that at least one of the premises is
false. It is not true that biologists have no evidence that
indirect Darwinian pathways exist. Dembski is closing his eyes to
all the palaeontological and biochemical evidence of co-option.
Co-option (also known as co-optation) is a
fundamental process of evolutionary biology in which structures
which have evolved for one use become employed for a different use.
One of the best known examples is the evolution of the mammalian
inner ear from reptilian jaw bones, an evolutionary sequence which
is clearly demonstrated by the fossil record. Simon Conway Morris,
a leading evolutionary biologist, writes:
Cooption is, therefore, commonplace (e.g., Finkelstein
and Boncinelli, 1994; Holland and Holland, 1999), perhaps
ubiquitous, and just what we would expect in organic
evolution. [7]
Indeed, co-option is not just advantageous but absolutely
essential to evolutionary theory. Complex new systems cannot appear
suddenly out of nowhere, so whenever an organism begins to do
something new, it must do so by co-opting an existing struture
which evolved for another use. This could be as simple as a fish
using its fins--which evolved for swimming--for scrambling over
rocks in shallow water. Over time, if the conditions persist,
natural selection may gradually lead to the fins becoming better
adapted for scrambling and less useful for
swimming. Eventually scrambling may become their primary
function.
Co-option has always been a thorn in the side of proponents
of the argument from irreducible complexity, as it negates their
simplistic arguments. In Darwin's Black Box, the first
book to elaborate the argument, Behe employed a dichotomy, dividing
evolutionary pathways into two groups, direct and
indirect, the same division that we see in Dembski's
recent articles. He presented a (rather muddled) argument against
evolution by direct pathways, while failing to come up with any
substantive argument at all against indirect pathways.
When Dembski employed his own version of the argument in No
Free Lunch, he abandoned the obfuscatory direct/indirect
dichotomy, apparently believing that he instead had a
knock-out argument against co-option. But the co-option
scenario which he argued against was a straw man, another
oversimplistic reading of evolutionary
theory. It hypothesized that all the proteins making up
the flagellum evolved independently for other purposes and were
then simultaneously co-opted to produce a flagellum. He failed to
consider the more realistic hypothesis that a substantial
exisiting system, consisting of many proteins, was co-opted as a
single unit. Yet this is exactly the type of hypothesis which
biologists propose. Having overlooked this possibility, Dembski
erroneously claimed that he had considered and rejected all
possible options, and that he had therefore decisively eliminated
Darwinian evolution as a reasonable explanation for the
flagellum:
These two conditions transform the definition of
irreducible complexity into a vise that allows the Darwinian
mechanism no room to maneuver. ... Let me stress that there is no
false dilemma here--it is not as though there are other options
that I have conveniently ignored but that the Darwinian mechanism
has at its disposal. [8]
Since the publication of No Free Lunch, Dembski's error
has been pointed out to him and he appears to have recognised it.
Though not acknowledging that he made a mistake or that he has
changed his argument, Dembski has abandoned the claim above and
fallen back on the argument from ignorance, while adopting Behe's
direct/indirect dichotomy as a new smokescreen. He also now
mentions the possibility which he previously overlooked:
But what if instead
co-option occurred more gradually and incrementally? In the
evolution of the bacterial flagellum, imagine natural selection
gradually co-opting existing protein parts into a single evolving
structure whose function co-evolves with the
structure.
Here, Dembski is still limiting evolution to
adding existing protein parts to a structure (why not
larger parts?), but at least he is now considering the possibility
that the function of the whole structure may change over time. Unfortunately
for him, however, the only argument he can find to use against this
possibility is another argument from ignorance:
Minimally what's
required are detailed, testable reconstructions or models that
demonstrate how indirect Darwinian pathways might reasonably
have produced actual irreducibly
complex biochemical machines like the bacterial
flagellum.
In No Free
Lunch Dembski appealed to a concept he called causal
specificity. Never one to eschew the opportunity to invent
another useless technical term, Dembski now replaces causal
specificity with causal adequacy:
This is where the argument from
irreducible complexity needs to make a third key point, namely, an
explanatory point. Scientific explanations come in many forms and
guises, but the one thing they cannot afford to be without
is causal
adequacy. A scientific
explanation needs to call upon causal powers sufficient to explain
the effect in question. Otherwise, the effect is unexplained. The
effect in question is the irreducible complexity of certain
biochemical machines. How did such systems come about? Not by
direct Darwinian pathways--irreducible complexity rules them
out on logical and mathematical grounds. And not by indirect
Darwinian pathways either--the absence of scientific evidence
here is as complete as it is for leprechauns. Nor does appealing to
unknown material mechanisms help matters, for in that case not only
is the absence of evidence complete but also the very theory for
which there's no evidence is absent as well.
Thus, when it comes to irreducibly
complex biochemical systems, there's no evidence that
material mechanisms are causally adequate to bring them about. But
what about intelligence? Intelligence is well known to produce
irreducibly complex systems (e.g., humans regularly produce
machines that exhibit irreducible complexity). Intelligence is
thus known to be causally adequate
to bring about irreducible complexity. The argument from
irreducible complexity's explanatory point, therefore, is
that on the basis of causal adequacy, intelligent design is a
better scientific explanation than the Darwinian mechanism for the
irreducible complexity of biochemical systems.
As usual, Dembski doesn't clearly define his term. A causally
adequate (or "sufficient") explanation might be taken to be one
which necessitates the observed outcome. But this is not
how Dembski uses the term. Clearly, an intelligent designer does
not necessitate the occurrence of irreducibly complex biological
systems. The designer might have chosen not to produce any
organisms at all. It appears that when Dembski says an explanation
is causally adequate he means that the causes invoked
by the explanation could have produced the result to be
explained. His claim then seems to be that natural
evolution could not have produced the irreducibly complex
biological systems that we observe, but an intelligent designer
could have done so. We have already seen that the first part of
this claim (that natural evolution could not have produced
irreducibly complex systems) is based on nothing more than an
argument from ignorance.
However, Dembski's argument here is not just about whether
certain causes could have produced the observed result,
but whether there is evidence that they could have done
so. He claims there is no evidence that natural evolution could
have produced irreducibly complex biochemical systems. This is
untrue. Presenting the evidence for natural evolution is far beyond
the scope of this article. Broadly speaking, it consists of the
multitude of examples of ad hoc adaptation of organisms to
their environmental conditions, adaptations which show no sign of
direction towards any goal. This evidence and the absence of
evidence for a designer make natural evolution the best explanation
of the biological systems we observe (irreducibly complex or
otherwise). In the absence of any good argument against the
natural evolution of irreducibly complex systems, there is no
reason to treat them as a special case. Furthermore, theoretical
evidence of the power of natural selection to produce complex
systems is provided by computerized evolutionary algorithms [9].
Dembski goes on to argue that intelligent design is known to be
causally adequate to explain irreducibly complex systems, based on
the assertion that "humans regularly produce machines that
exhibit irreducible complexity". Let's accept for the sake of
argument that humans really do produce machines that exhibit
irreducible complexity in Dembski's sense of the term
(though he gives no examples). It does not follow that an
intelligent designer could have produced the irreducibly complex
biological systems that we observe. Dembski offers no
evidence of the capabilities of any designer who was in
a position to design biological systems. Nor does he offer any
evidence that such a designer could have existed.
Thus, Dembski is very far from demonstrating the causal
adequacy of his explanation. He is just resorting
to an old chestnut of religious apologetics in which divine
explanations are invoked while ignoring all the explanatory
problems associated with the nature and existence of gods.
Replacing "divine" with "design" does not make this style of
argument any more convincing.
In his latest article, Dembski repeats the claim--made in
many previous articles and books--that his notion of specified
complexity provides a reliable criterion for detecting design.
I dealt with this claim at great length in my critique of No
Free Lunch [3], showing that Dembski's use of the term specified
complexity was equivocal and deceptive, serving only as a
smokescreen for his god-of-the-gaps argument. I will give an
updated but much briefer treatment of the subject here.
The first thing to note is that Dembski does not use the word
complexity in its everyday sense, nor in any pre-existing
technical sense. Instead, he uses it in a misleading sense of his
own: for Dembski, complexity is defined to
mean improbability. He also uses the word
information in the same idiosyncratic sense. As a result,
Dembski's specified complexity and information
have quite different meanings from these same terms as used by
other writers. Yet Dembski shamelessly conflates his own
idiosyncratic meaning with those others, causing endless confusion.
Of course, when Dembski means improbability, he should write
"improbability", and not mislead his readers by calling it
complexity or information.
Further confusion is caused by Dembski's persistent refusal to
clarify what improbability he is referring to. Sometimes he seems
to mean the improbability of an event with respect to a specific
natural hypothesis, and usually this is a hypothesis involving a
uniform probability distribution, such as a hypothesis of purely
random combination of components. At other times, he seems to
mean that an event is complex if it is improbable with respect to
all the natural hypotheses we can think of. At still other times,
he seems to mean that an event is complex if it is improbable with
respect to all possible natural causes.
In his latest article, Dembski continues his policy of
equivocation. First he writes that:
Darwinists object to this
approach to establishing the specified complexity of irreducibly
complex biochemical systems. They contend that design theorists, in taking this approach,
have merely devised a 'tornado-in-a-junkyard'
strawman.
What evolutionists object to is the habit
that antievolutionists have of calculating a probability based
on a hypothesis of purely random combination and then presenting this
as the probability of the system evolving. Dembski performed
just such a calculation in No Free Lunch [10], but has
been extremely vague about just what relevance it has to his
argument. In previous articles, he has implied that this
probability calculation takes natural selection into account, even
though it does not do so:
Convinced that the Darwinian
mechanism must be capable of doing such evolutionary design work,
evolutionary biologists rarely ask whether such a sequence of
successful baby-steps even exists; much less do they attempt to
quantify the probabilities involved. I attempt that in chapter 5 of
my most recent book No Free Lunch . There I lay out
techniques for assessing the probabilistic hurdles that the
Darwinian mechanism faces in trying to account for complex
biological structures like the bacterial flagellum. The
probabilities I calculate--and I try to be conservative--are
horrendous and render natural selection entirely implausible as a
mechanism for generating the flagellum and structures like
it. [11]
He includes a similarly deceptive
implication in his latest article:
Yet even with the most generous
allowance of legitimate advantages, the probabilities computed for
the Darwinian mechanism to evolve irreducibly complex biochemical systems like the bacterial
flagellum always end up being exceedingly small.29
Footnote 29 here is Dembski's, and refers to
section 5.10 of No Free Lunch, the whole of which
is concerned with a probability calculation based on a
hypothesis of purely random combination. In fact, Dembski
misleadingly fails to state in No Free Lunch that his
calculation is based on such a hypothesis (even though his general
method of inferring design requires him to identify "all the
relevant chance hypotheses" [12]), but it follows from an analysis of
the calculation, and he has since acknowledged that this is
the case:
Wein therefore does not dispute my calculation of
appearance by random combination, but the relevance of that
calculation to systems like the
flagellum. [4]
This is the only probability calculation which
Dembski has ever provided for the origin of a biological
system. In his latest article, he gives a lengthy description of
how one might go about performing such a probability calculation,
and his aim here does seem to be to take natural selection into
account. But his discussion remains purely theoretical, since
he does not provide any figures.
He also lists a number of
alleged hurdles that evolution must overcome. These
are all rather vague and based on oversimplistic views of
evolutionary biology. Some of them also involve more appeals to
ignorance. I won't deal with them individually. As long as the
argument from irreducible complexity remains the mainstay of
Intelligent Design advocates, there is no reason why critics should
spend their time dealing with additional arguments which are
presented only vaguely. If Dembski believes he has found a better
argument than the argument from irreducible complexity, let him say
so and present it in a professional manner.
The arguments for Intelligent Design are
purely negative. Rather than offer evidence of the existence of any
designer, they attempt to rule out natural evolution of
certain biological structures. One such argument, the current
favourite of the Intelligent Design movement, is the argument from
irreducible complexity. However, instead of addressing evolutionary
theory as actually propounded by evolutionary biologists, the
substantive part of the argument is aimed at a
simplistic parody of the theory which ignores one of
its most fundamental elements, namely co-option of existing
structures. The remainder of the argument is just a disguised
version of the old argument from ignorance, or god-of-the-gaps
argument. Intelligent Design advocates are forced to rely on the
god-of-the-gaps argument because they are committed
to detecting the action of an intelligent designer in
biology despite the inescapable fact that no evidence of
such a designer exists.
1. William Dembski, No Free Lunch: Why
Specified Complexity Cannot be Purchased without Intelligence,
Rowman & Littlefield, 2002.
2. Michael
Behe, Darwin's Black Box (Simon & Schuster, 1998), pp.
39-40.
3. Richard Wein, "Not a Free Lunch But a Box of Chocolates: A
critique of William Dembski's book No Free Lunch", The
Talk.Origins Archive, May 2002,
http://www.talkorigins.org/design/faqs/nfl. Also posted at TalkReason.
4. William Dembski, "Obsessively Criticized But Scarcely
Refuted: A Response To Richard Wein", May 2002,
http://www.designinference.com/documents/05.02.resp_to_wein.htm.
See also my response to this article:
Richard Wein, "Response? What Response? How Dembski has avoided
addressing my arguments", The Talk.Origins Archive, May 2002, http://www.talkorigins.org/design/faqs/nfl/replynfl.html. Also posted at TalkReason.
5. William Dembski, "The Fantasy Life of Richard Wein: A
Response to a Response", June 2002,
http://www.designinference.com/documents/2002.06.WeinsFantasy.htm.
6. William Dembski, "Irreducible Complexity Revisited", January
2004,
http://www.designinference.com/documents/2004.01.Irred_Compl_Revisited.pdf.
7. Simon Conway Morris, "Evolution: Bringing Molecules into the
Fold", Cell, Vol. 100, 1-11.
8. No Free Lunch, p. 287.
9. Richard Lenski, Charles Ofria, Robert Pennock & Christoph
Adami, "The evolutionary origin of complex features", Nature, May
2003.
10. No Free Lunch, pp. 289-302.
11. William Dembski, "Does Evolution Even Have a Mechanism?",
April 2002, http://www.designinference.com/documents/04.02.AMNH_debate.htm.
12. No Free Lunch, pp. 72 & 123.
