Boston Review
March 1, 1997
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.
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