More Articles on Evolution
The Sterility of Darwinism
Michael J. Behe
As it struggles to comprehend nature,
science sometimes has to completely re-think how the world works.
For example, Newton's laws apply to everyday objects but can't
handle nature's tiny building blocks. Propelled by this discovery,
quantum mechanics overthrew Newton's theory. Revolutions in biology
have included the cell theory of life in the 19th century, as
well as the slow realization in this century that cells are composites
of enormously complex molecular systems.
Newton's theory remains very useful,
and we can still learn many things by studying whole animals or
cells. When explaining the nuts and bolts of the world, however,
those views must yield to more basic descriptions. A mechanical
engineer can't contradict a physicist on fundamental principles
of matter. And evolutionary biology can't overrule biochemistry1 on fundamental principles of life. It's not a question of pride--that's
just the way the world works.
Curiously, some people seem offended
by the way the world works. In his review of my book, Darwin's
Black Box: The Biochemical Challenge to Evolution, evolutionary
biologist H. Allen Orr unexpectedly attempts to claim priority
for his field. He grouses that pre-med students are required to
take biochemistry but not evolutionary biology. He plaintively
asks "Why is everyone an expert witness when the topic is Darwinism
but not when it's biochemistry?" The obvious reply is that the
evolution of biochemical systems is itself biochemistry. When
a protein sequence changes, when DNA mutates, those are biochemical
changes. Since inherited changes are caused by molecular changes,
it is biochemists--not evolutionary biologists--who will ultimately
decide whether Darwin's mechanism of natural selection can explain
life. No offense--that's just the way the world works.
Orr hankers for the respect accorded
physicists, and thinks evolutionary biologists can finally lay
aside their "physics envy" because "we biologists have discovered
the structure of DNA, broken the genetic code, sequenced the entire
genome of some species . . ." Orr is like a podiatrist claiming
credit for progress in brain surgery. Biochemistry made
those dramatic advances; evolutionary biology played no part.
I mean no disrespect, but this is not a minor academic turf war--the
point is crucial. Anyone who wants to address questions about
life's basic mechanisms has to do so from a molecular perspective.
Orr does not.
Declining the opportunity to address
my biochemical arguments, Orr questions the concept of irreducible
complexity on logical grounds. He agrees with me that "You
cannot . . . gradually improve a mousetrap by adding one part
and then the next. A trap having half its parts doesn't function
half as well as a real trap; it doesn't function at all." So Orr
understands the point of my mousetrap analogy--but then mysteriously
forgets it. He later writes, "Some part (A) initially does some
job (and not very well, perhaps). Another part (B) later gets
added, because it helps A." Some part initially does some
job? Which part of the mousetrap is he talking about? A mouse
has nothing to fear from a "trap" that consists of just an unattached
holding bar, or spring, or platform, with no other parts.
I do sympathize with Orr's muddling
of the analysis. The concept of irreducible complexity is new,
and can be difficult to grasp for people who have always assumed
without demonstration that small, continuous changes could produce
virtually any biological structure. Perhaps in the future that
assumption will not have such a strong hold on the minds of evolutionary
biologists.
Having completed his logical analysis,
Orr turns to the topic of gene duplication: "So how does Behe
explain duplicate genes? He doesn't." But I do. I discuss them
on pages 89-90 of my book, concluding "The sequence similarities
are there for all to see. . . . By itself, however, the hypothesis
of gene duplication . . . says nothing about how any particular
protein or protein system was first produced." For example, the
DNA in each of the antibody-producing cells of your body is very
similar to that of the others, but not identical. The similarities
are due to common descent; that is, all the cells in your body
descended from one fertilized egg cell. The differences, however,
are not due to Darwinian natural selection. Rather, there is a
very clever, built-in program to rearrange antibody genes. Billions
of different kinds of antibody genes are "intentionally" produced
by your body from a pre-existing stock of just a few hundred gene
pieces. Perhaps because of his unfamiliarity with molecular systems,
Orr has trouble seeing that similarity in gene sequences may indicate
common ancestry, but is not itself evidence that a system was
constructed by natural selection.
To test natural selection requires
much more evidence than mere sequence similarity: it requires experimentation.
In all of the scientific literature, however, no experimental
evidence can be found that natural selection can produce irreducibly
complex biochemical systems. To rebut my arguments Orr could simply
have cited papers in the science literature where the systems I
discuss have been explained. He didn't do that because explanations
are nowhere to be found. *
* *
What has biochemistry found that
must be explained? Machines--literally, machines made of molecules.
Let's look at just one example. The flagellum is an outboard motor
that many bacteria use to swim. It consists of a rotary propeller,
motor, and stationary framework. Yet this short description can't
do justice to the machine's full complexity. Writing of the flagellum
in Cell,2 Lucy Shapiro of Stanford University
marvels, "To carry out the feat of coordinating the ordered expression
of about 50 genes, delivering the protein products of these genes
to the construction site, and moving the correct parts to the
upper floors while adhering to the design specification with a
high degree of accuracy, the cell requires impressive organizational
skills." Without any one of a number of parts, the flagellum does
not merely work less efficiently; it does not work at all. Like
a mousetrap it is irreducibly complex and therefore cannot have
arisen gradually.
The rotary nature of the flagellum
has been recognized for about 25 years. During that time not a
single paper has been published in the biochemical literature
even attempting to show how such a machine might have developed
by natural selection. Darwin's theory is completely barren when
it comes to explaining the origin of the flagellum or any other
complex biochemical system.
The sterility of Darwinism indicates
that it is the wrong framework for understanding the basis of
life. As I argue in my book, an alternative hypothesis is both
natural and obvious: systems such as the flagellum were intentionally
designed by an intelligent agent. Just as in the everyday world
we immediately conclude design when we see a complex, interactive
system such as a mousetrap, there is no reason to withhold the
same conclusion from interactive molecular systems. This conclusion
may have theological implications that make some people uncomfortable;
nonetheless it is the job of science to follow the data wherever
they lead, no matter how disturbing.
One last charge must be met: Orr
maintains that the theory of intelligent design is not falsifiable.
He's wrong. To falsify design theory a scientist need only experimentally
demonstrate that a bacterial flagellum, or any other comparably
complex system, could arise by natural selection. If that happened
I would conclude that neither flagella nor any system of similar
or lesser complexity had to have been designed. In short, biochemical
design would be neatly disproved.
Let's turn the tables on Orr. Is
natural selection falsifiable? He writes, "We have no guarantee
that we can reconstruct the history of a biochemical pathway.
But even if we can't, its irreducible complexity cannot count
against its gradual evolution. . . ." This is a dangerously antiscientific
attitude. In effect he is saying, "I just know that phenomenally
complex biochemical systems arose gradually by natural selection,
but don't ask me how." With such an outlook, Orr runs the risk
of clinging to ideas that are forever insulated from contact with
the outside world.
After reading Robert Berwick's criticism
of Climbing Mount Improbable, I find myself in the odd position
of sympathizing with Richard Dawkins. Although his book is a juicy
target for debunking, Berwick chides Dawkins for all the wrong reasons.
Berwick points out that natural selection is sometimes not a complete
explanation for some biological feature. For example, he writes
that polioviruses have shapes like geodesic domes not because selection
made them that way, but because the symmetrical shape is required
by physical law. Well, fine. But there are many tasks a virus faces
that are not explained at all by simple physical laws: The virus
has to attach to a cell surface, inject its genetic material into
the cell, hijack the cell's machinery, make copies of the poliovirus
DNA, and re-package the genetic material. In response the body's
immune system launches a counterattack to ferret out and destroy
the virus. None of these processes is explained by simple
physical constraints. Berwick seems mesmerized by the simple crystal
that covers nature's watch, and ignores the complex ticking gears
of the mechanism within. Dawkins's writing should be roundly criticized
for failing to answer the question he has set himself: what is the
origin of biological complexity? But, to his credit, Dawkins at
least knows the important question. Berwick doesn't.
1 By biochemistry
I mean all sciences that investigate life at the molecular
level, including molecular biology, much of embryology, immunology,
genetics, etc.
2 Lucy Shapiro,
"The Bacterial Flagellum: From Genetic Network to Complex Architecture,"
Cell 80 (1995): 525-27.
Originally published in the February/
March 1997 issue of Boston Review
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