articles on evolution
in Boston Review
Darwin v. Intelligent Design
The latest attack on evolution
is cleverly argued, biologically informed—and wrong
H. Allen Orr
Darwin's Black Box: The Biochemical
Challenge to Evolution
Michael J. Behe
Free Press, $25
Just don't pull the knot tight before
being certain that you have got hold of the right end.
The pages of this magazine are not often taken up with reviews
of creationist screeds. The stuff is, after all, intellectual
junk food, served up with a transparent evangelical agenda. But
now and then a reputable, or even esteemed, scientist launches
an assault on evolution. These attacks are potentially important
and, whether sound or not, are invariably great head-turners.
A generation ago, for instance, the astronomer Sir Fred Hoyle
announced that the theory of natural selection was deeply flawed
and could never account for the existence of complex organisms
like you and me. Hoyle's objections were frankly silly, reflecting
an embarrassing misunderstanding of Darwinian logic. In retrospect,
there was only one reason anyone listened: Hoyle was a physicist.
And as everyone—including biologists—then knew, physicists
are smarter than the rest of us.
But the days of biologists suffering
physics envy are long gone. We biologists have discovered the
structure of DNA, broken the genetic code, sequenced the entire
genome of some species, and, to a remarkable extent, figured out
how a little egg turns into a big person (the last in a breathtaking
decade). If a Hoyle were to now announce that biologists are deeply
confused about natural selection or neurobiology, he'd be greeted,
if at all, with a big yawn. There's only one way to shake up biologists
now—the attack has to come from within.
Well, ask and ye shall receive.
Michael J. Behe, a biochemist at Lehigh University, has published
a (seemingly) sophisticated insider's attack on Darwinism. His
book, Darwin's Black Box, is well-written, cleverly argued, and
biologically informed. No one can deny Behe's grasp of biochemistry.
Unlike a few previous "biologists" who have taken aim
at Darwin, Behe is the real thing: a research scientist, someone
who does experiments, gets grants, and publishes papers. Behe's
work may well represent the most sophisticated—and the most
seductive—creationist attack on evolution in a quarter century.
But Behe, it turns out, differs from his less-sophisticated brethren
in an important way: he does not wholly deny evolution. He has
no problem with stories of moths evolving dark coloration so as
to hide on polluted trees or of streptococci outwitting antibiotics.
Nor does he deny common descent, the notion that all species,
including humans, are derived from one or a few common ancestors.
But Behe's chief claim remains deeply revolutionary: evolution,
he says, cannot account for the cell, the very basis of life.
Instead the cell shows unequivocal signs of design by an intelligent
Not surprisingly, Behe has gotten
a bit of attention. His book is, after all, a creationist's dream
come true. His challenge to Darwin has been talked up in Newsweek,
U.S. News & World Report, the New York Times, and National
Review. Even Judge Bork has chimed in, proclaiming that Behe "has
shown that Darwinism cannot explain life as we know it."2
(Revealing his expertise on such things, Bork misidentifies Behe
as a "microbiologist," not a biochemist.) Whether or
not Behe wanted such company, it is obvious that the Christian
Right and allied conservative forces will make much ado of his
book. There's a brand new weapon in the creationist arsenal—a
real biologist says we're right.
Although Behe discusses his religious
sentiments—he notes his Roman Catholicism, is disturbed by the
ill will between science and theology, and is subtly (but clearly)
offended by biologist Richard Dawkins's atheism—he never places
himself squarely in the creationist camp.3 He
maintains that his position is strictly scientific and that the
data have driven him ineluctably to his views. As though to prove
his scientific restraint, Behe even refuses to speculate on the
identity of the designer. Although his last chapter offers many
hints of the designer's divinity, the door is left open ever so
slightly to some variety of alien intervention (although one wonders
who designed them). It's hard to say if Behe's reluctance to utter
"God did it" is tactical or sincere. On the one hand,
creationists learned long ago to be discreet about religious motive.
But on the other, Behe seems sophisticated enough to see that
Darwinism never threatened any but the most literal-minded of
religious creeds anyway (as dramatically confirmed by Pope John
Paul II's recent acceptance of evolution as "more than just
In any case, I will take Behe at
his word. His arguments should and must be dealt with on scientific
grounds, just as he has requested. For, in the end, Behe is simply
right or wrong. And I am convinced that he is very wrong.
Until recently, we had no inkling
of what went on inside a cell. Although biology had made great
strides in anatomy and physiology, the cell remained a tightly
shut black box. Behe argues that this black box proved very convenient
to evolutionists: when explaining, say, the evolution of the eye,
biologists could start their story with a light-sensitive cell
of the sort that lines our retinas. Evolutionists then merely
tried to explain how the gross morphology of the eye—a curved
retina, a properly shaped lens—evolved. No one interrupted such
tales to ask, "But how do you get a light-sensitive cell
in the first place?" The question was not asked, Behe argues,
because everyone believed the inner workings of the cell to be
trivially simple—certainly nothing that might pull the rug out
from under Darwinism.
But in the early 1950s, the heroes
of Behe's book, the biochemists, began to pry open the black box,
working out the structure and function of molecules residing in
the cell. Decades of such work have unearthed two findings that
Behe claims are of capital importance to evolution. First, the
cell is horrendously complicated. Indeed Behe spends a third of
his book trying to convince you of just how complicated it is.
Take your pick—blood clotting, intracellular transport, the immune
response (a chapter each)—they're all Rube Goldberg machines of
As Behe tells it, the complexity
of the cell came as a big surprise. But his display of shock is,
I think, a bit disingenuous, an attempt to create a crisis atmosphere.
To anyone paying attention over the last century, the revelation
of complexity is no revelation at all. Geneticists, for instance,
have known for sixty years that the modest fruitfly sports at
least five thousand genes. So how could it not be complicated?
You don't need a script to know that a play featuring five thousand
speaking parts is going to be a tad complicated. Moreover, evolutionists
all know that, from the time the earth formed, it took three billion
years to evolve the first true cell but only half as long to get
human beings from this cell. And we all interpret this the same
way: it's harder to evolve a cell than a human given a cell. But,
surprise or no, Behe's talk of complexity is utterly beside the
point. As he well knows, Darwinism has no trouble explaining sheer
complexity: four billion years is an unimaginably long time for
things to get complicated.
Behe's second point is far more
important. Biochemistry, he claims, has revealed not just complexity,
but a special kind of complexity: many biochemical systems are
irreducibly complex. Because it represents the central argument
of his book—and the key to his attack on Darwinism—it is important
to see what Behe means here. "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 stop
functioning." Consider Behe's favorite example: the mousetrap.
A mousetrap has a clear function (crushing mice) and is made of
several parts (a platform, a spring, a bar that does the crushing).
If any of these parts is removed, the trap doesn't work. Hence
it's irreducibly complex. This is different from, say, a car,
which continues to run after a headlight burns out or a spark
plug stops firing.
One of Behe's goals is to show that
irreducible complexity is not confined to the inanimate world:
some biochemical systems are also irreducibly complex. Here he
succeeds. Certain biochemical systems show exactly the properties
Behe attributes to them. His description of the mind-boggling
cascade of reactions that occurs during blood-clotting is particularly
persuasive: thrombin activates accelerin, which, with Stuart factor,
cleaves prothrombin; the resulting thrombin cleaves fibrinogen,
making fibrin, etc. Knock out any of these innumerable steps and
the animal either bleeds or clots to death.
To Behe, an extraordinary conclusion
follows on the heels of irreducible complexity: Darwinism cannot
explain such systems. The reason, he says, is simple: An irreducibly
complex system "cannot be produced directly . . . by slight,
successive modifications of a precursor system, because any precursor
to an irreducibly complex system that is missing a part is by definition
nonfunctional." You cannot, in other words, 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 Darwinism's problem is obvious: it requires
that each step in the evolution of a system be functional and adaptive.
Biochemistry has, then, found an "unbridgeable chasm"—evolution
just can't get here from there. Indeed Darwinism is rendered so
impotent before irreducible complexity that Behe feels obliged to
resurrect a notion that, since Darwin, has been the greatest of
all biological taboos—intelligent design. The cell, he argues, is
a mousetrap: a complex machine bearing the unmistakable signature
of an intelligent designer.5
Originally published in the December
1996/ January 1997 issue of Boston Review
So the question facing biologists
is clear: Do irreducibly complex systems represent an unbridgeable
evolutionary chasm? If so, Darwinism is in a bad way and Behe
has made an astonishing discovery. If not, Behe's case collapses
and he has succeeded only in misleading large numbers of people.
Behe, never shy, has already cast his vote: the discovery of design,
he assures us, is "so significant that it must be ranked
as one of the greatest achievements in the history of science,"
rivaling "those of Newton and Einstein, Lavoisier and Schrodinger,
Pasteur, and Darwin."
The first thing you need to understand
about Behe's argument is that it's just plain wrong. It's not
that he botched some stray fact about evolution, or that he doesn't
know his biochemistry, but that his argument—as an argument—is
fatally flawed. To see this we need to first get clear about what
kinds of solutions to irreducible complexity are not open to Darwinism.
First it will do no good to suggest that
all the required parts of some biochemical pathway popped up simultaneously
by mutation. Although this "solution" yields a functioning
system in one fell swoop, it's so hopelessly unlikely that no
Darwinian takes it seriously. As Behe rightly says, we gain nothing
by replacing a problem with a miracle. Second, we might think
that some of the parts of an irreducibly complex system evolved
step by step for some other purpose and were then recruited wholesale
to a new function. But this is also unlikely. You may as well
hope that half your car's transmission will suddenly help out
in the airbag department. Such things might happen very, very
rarely, but they surely do not offer a general solution to irreducible
Behe's colossal mistake is that, in rejecting
these possibilities, he concludes that no Darwinian solution remains.
But one does. It is this: An irreducibly complex system can be
built gradually by adding parts that, while initially just advantageous,
become—because of later changes—essential. The logic is very simple.
Some part (A) initially does some job (and not very well, perhaps).
Another part (B) later gets added because it helps A. This new
part isn't essential, it merely improves things. But later on,
A (or something else) may change in such a way that B now becomes
indispensable. This process continues as further parts get folded
into the system. And at the end of the day, many parts may all
The point is there's no guarantee that
improvements will remain mere improvements. Indeed because later
changes build on previous ones, there's every reason to think
that earlier refinements might become necessary. The transformation
of air bladders into lungs that allowed animals to breathe atmospheric
oxygen was initially just advantageous: such beasts could explore
open niches—like dry land—that were unavailable to
their lung-less peers. But as evolution built on this adaptation
(modifying limbs for walking, for instance), we grew thoroughly
terrestrial and lungs, consequently, are no longer luxuries—they
are essential. The punch line is, I think, obvious: although this
process is thoroughly Darwinian, we are often left with a system
that is irreducibly complex. I'm afraid there's no room for compromise
here: Behe's key claim that all the components of an irreducibly
complex system "have to be there from the beginning"
is dead wrong.
It's worth noting that our scenario is
neither hypothetical nor confined to the often irretrievable world
of biological history. Indeed it's a common experience among computer
programmers. Anyone who programs knows how easy it is to write
yourself into a corner: a change one makes because it improves
efficiency may become, after further changes, indispensable. Improvements
might be made one line of code at a time and, at all stages, the
program does its job. But, by the end, all the lines may be required.
This programming analogy captures another important point: If
I were to hand you the final program, it's entirely possible that
you would not be able to reconstruct its history—that this line
was added last and that, in a previous version, some other line
sat between these two. Indeed, because the very act of revising
a program has a way of wiping out clues to its history, it may
be impossible to reconstruct the path taken. Similarly, 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 any more than the irreducible
complexity of a program does—which is to say, not at all.
I wish I could claim credit for this Darwinian
model of irreducible complexity, but I'm afraid I've been scooped
by eighty years. This scenario was first hinted at by the geneticist
H. J. Muller in 1918 and worked out in some detail in 1939.6
Indeed, Muller gives reasons for thinking that genes which at
first improved function will routinely become essential parts
of a pathway. So the gradual evolution of irreducibly complex
systems is not only possible, it's expected. For those who aren't
biologists, let me assure you that I haven't dug up the half-baked
lucubrations of some obscure amateur. Muller, awarded the Nobel
Prize in 1946, was a giant in evolution and genetics.
Although Muller's essay isn't as well known
as it should be, the gist of his idea is common wisdom in evolutionary
biology. Here's an important application: Molecular evolutionists
have shown that some genes are duplications of others. In other
words, at some point in time an extra copy of a gene got made.
The copy wasn't essential—the organism obviously got along fine
without it. But through time this copy changed, picking up a new,
and often related, function. After further evolution, this duplicate
gene will have become essential. (We're loaded with duplicate
genes that are required: myoglobin, for instance, which carries
oxygen in muscles, is related to hemoglobin, which carries oxygen
in blood. Both are now necessary.) The story of gene duplication—which
can be found in every evolution text—is just a special case of
Muller's theory. But it's an immensely important case: it explains
how new genes arise and, thus, ultimately, how biochemical pathways
So how does Behe explain duplicate genes?
He doesn't. He reluctantly admits that different genes often have
similar sequences. He even admits that some genes in his favorite
pathway—blood clotting—are similar.7 But he refuses
to draw the obvious conclusion: some genes are copies of others.
Does Behe think their similarity is a coincidence—they just happen
to look alike? It is, I think, clear why Behe fails to face up
to duplicate genes: were he to admit that one gene is a copy of
another, he'd have to admit that a copy was made at some point
in time and thus that the organism once got along without it.
But this implies that such systems can arise step by step. Behe
avoids this conclusion only by sheer evasion: he brands gene duplication
a "hypothesis," leaves the similarity of his favorite
genes unexplained, and quickly moves on to safer turf.
In truth, we're done. Behe's chief objection
to Darwinism is flat wrong, and, bereft of this, he's got little
to say. But when you do look at what else he says, you find a
bizarre string of confusions and contradictions.
For instance, while Behe claims that evidence
for design had to await the new science of biochemistry, he never
really explains what's so special about biochemistry. It's true
that molecules provide some nice examples of irreducible complexity,
but why can't we find such complexity at other levels? The answer
is we can. Here's one: the heart. The human heart is built of
a pump and valves. Remove either one and you're dead. But Behe
seems terribly unclear about whether such non-molecular examples
are kosher. In one breath, he tells us that "one has to examine
molecular systems for evidence of design," but in the next,
he assures us that the theologian William Paley's description
of the heart as irreducibly complex was right on the money. So
which is it? If Paley's example is "exactly correct,"
why did we have to await biochemistry? The issue is not trivial.
For if anatomy didn't topple Darwinism (and it seems not to have),
why should biochemistry?
Behe's one attempt to explain what's so
special about molecules only hurls us into deeper confusion. He
suggests that biochemical examples are best because they're simpler
and thus clearer. But I, for one, have a hard time reconciling
this argument with Behe's main claim—that biochemistry is
very, very complicated. I suspect the real reason Behe finds biochemistry
so special is that he has confused two senses of "reducible."
Irreducible complexity is a formal property of a system, having
nothing to do with physical scale. You might say we can't "reduce"
the function of the system to its parts if they're all required.
But if we like, we can always "reduce" such a system
into its molecular bits and pieces (the heart is made of myosin,
etc.). When Behe worries that an anatomical structure is made
of so many different molecules that it's hard to know if it's
irreducibly complex, he is mixing up these two senses of reducible.
There is absolutely no reason to think we get truer irreducible
complexity at the micro than macro scale. This is made perfectly
clear by Behe's own example: to see that a mousetrap is irreducibly
complex, we don't have to work out its chemistry! It remains irreducibly
complex whether made of one kind of molecule or one million. The
upshot is that Behe's grand claim that biochemistry poses some
qualitatively new challenge to Darwinism just doesn't make sense.
Irreducible complexity lives at all scales.
Behe offers up yet another contradiction
when he tells us that he finds the descent of all species from
a common ancestor "fairly convincing" but that he's
not so sure about macroevolution.8 Now macroevolution
is the process of getting species from a common ancestor. You
can no more believe in one but not the other than you can believe
in beer but not brewing. The strange thing is that Behe seems
to understand the meaning of both words. He says sensible things
about common descent and then about macroevolution. He just doesn't
see that the two sets of statements are flatly contradictory.
Last, in one of the stranger passages of
his book, Behe speculates that the designer provided the Primal
Cell with all the genes modern organisms might need (i.e., the
first bacterium carried genes for human speech centers). If a
lineage didn't need some genes, they got lost or silenced. This
notion leaves so much of molecular evolution unexplained that
it's hard to know where to start. Here's just one problem: Although
some genes do get killed or silenced over time (producing non-functional
"pseudogenes"), how come we only carry pseudogenes that
are wrecked copies of our real genes? In other words, why don't
I carry pseudogenes for chlorophyll or flower structure? Why don't
azaleas carry pseudogenes for brain cells? Behe's it-was-all-there-from-day-one
hypothesis is flatly falsified by this and every other known pattern
in molecular evolution.
I'll be the first to admit that such non
sequiturs are not fatal to Behe's central argument. But they do
betray remarkable confusion or, worse, a powerful tendency to
see what he wants, contradictions be damned. In any case, strings
of such contradictions eat away at Behe's case, and, in the end,
make it hard to believe that Darwin will be getting company in
Westminster Abbey any time soon.
Know Thy Enemy
One of the most interesting questions about
Behe's book is why he feels especially qualified to critique Darwinism.
(And not just to quibble over details, but to announce that "Darwinism
is not science," as he did in a recent letter to Commentary.)9
To a historian or electrician, Behe certainly looks qualified.
He is a biologist. But it's not that simple, as can be seen by
turning the tables for a moment. If I, an evolutionary biologist,
were to announce that biochemistry is deeply flawed—I've shown,
for instance, that enzymes are not catalysts—I doubt I'd get a
listen. I surely wouldn't get a publisher. Nor would any jurist
consider my ruminations worthy of attention. But Behe stars in
public debates, has a fancy publisher (Free Press, a division
of Simon & Schuster) and the ear of the likes of Judge Bork.
Why the difference? Why is everyone an expert witness when the
topic is Darwinism but not when it's biochemistry?
The answer is complicated, but a few things
are clear. First, Darwinism matters. Many people will inevitably
have questions about Darwinism because many people will inevitably
think about it. By comparison, I doubt many Sunday school classes
get worked up over enzyme kinetics. Second—and this has more to
do with attacks from scientists such as Behe's—there's a striking
asymmetry in molecular versus evolutionary education in American
universities. Although many science, and all biology, students
are required to endure molecular courses, evolution—even introductory
evolution—is often an elective. The reason is simple: biochemistry
and cell biology get Junior into med school, evolution doesn't.
Consequently, many professional scientists know surprisingly little
Now I don't pretend to know the details
of Behe's education, but I do know this: he is not at home in
the technical evolution literature. His book reveals that his
grasp of evolution derives mostly from the pop literature (Gould,
Dawkins—good stuff, but no stand-in for the real thing)
and from computer searches of the scientific literature that he
strangely makes a big deal of. While I have utter confidence in
Behe's biochemistry, I am less confident that he can say what
soft selection, or Muller's ratchet, or the Fundamental Theorem
of Natural Selection is—all bread and butter of evolutionary biology.
It would be easy, of course, to get carried away here, and I want
to emphasize that I'm not saying that outsiders can offer nothing
of value (it's worth remembering that Darwin himself was trained
primarily as a geologist, not a biologist). I'm simply saying
that any would-be critic of Darwinism should know as much about
evolution as any critic of biochemistry must know about molecules.
(An idea that apparently never occurred to Free Press, who presumably
will next treat us to a botanist's musings on the flat earth.)
Finally, Behe and others may feel obliged
to sling mud Darwin's way because they suspect evolutionary biologists
won't do so. Evolutionists are widely perceived as uncritical
ideologues, devoted to suppressing all doubt about evolution.
It's easy to see how this impression arose: evolutionists, after
all, spend most of their public lives defending Darwin against
endlessly recycled creationist arguments. So of course we appear
hide-bound reactionaries. (So would physicists if the theory of
gravity were dragged into court every other year.) But the truth
is, I think, quite different. It would be fatuous to deny that
scientists can be intellectually conservative or prone to hero
worship. And it would be equally absurd to suggest that evolutionists
have resolved every major problem facing us; many remain. But
the fact is that, as in any science, evolutionists often sharply
disagree. And, as in any science, these disagreements sometimes
concern fundamentals. In the 1930s, for example, Sewall Wright
championed the role of "genetic drift" in evolution.
Parting with accepted wisdom, he argued that random changes in
the genetic composition of populations—not natural selection—account
for many of the differences we see between species. More recently,
Motoo Kimura championed the neutral theory, arguing that a good
deal of evolution at the molecular level does not reflect natural
selection. Here were overt attempts to circumscribe the role of
selection. And the attempts were largely successful: Wright and
Kimura were not hooted down, gagged or shot. Instead genetic drift
and the neutral theory are now enshrined in every evolution text.
So when the Christian Right tries to tell
you that evolutionists instinctively circle the wagons whenever
anyone dares question the Darwinian status quo, you should ask
yourself why Wright and Kimura got through, but Behe not. The
answer is, I think, straightforward: Wright and Kimura knew what
they were talking about. <
1 Notebooks, 1914–16,
ed. G. H. von Wright and G. E. M. Anscombe (Oxford: Blackwell,
1961), p. 47.
2 Robert H. Bork, Slouching
Towards Gomorrah: Modern Liberalism and American Decline (New
York: Regan Books, 1996), p. 294.
3 Also see Behe's New
York Times op-ed (October 26,1996, p. A25), where he speaks
more plainly about his religion.
4 New York Times,
October 25, 1996, p. A1.
5 Behe waffles a bit here.
He typically claims that irreducibly complex systems "cannot"
by natural selection as all the parts have to be there
from the beginning. But, once or twice, he contradicts these strong
claims, asserting that no Darwinian explanation seems possible.
The same waffling shows up in his New York Times op-ed,
where he boldly states that we know of "no other mechanism [besides
design], including Darwin's, which produces such complexity,"
and that "such a systemprobably cannot be put together
in a Darwinian manner" (my italics). For present purposes, the
distinction doesn't matter much: we'll see that it's neither impossible
nor difficult to gradually evolve irreducible complexity.
6 H. J. Muller, "Reversibility
in Evolution Considered from the Standpoint of Genetics," Biological
Reviews 14 (1939): 261–80. Muller does not, of course,
use Behe's term "irreducible complexity." Rather he speaks in
terms of irreversibility: you can add something extra because
it's merely advantageous. But, once it becomes essential, you
can't remove it. Irreducible complexity means that evolution is
7 The situation is slightly
more complex than this applies. Sometimes just parts of
genes get duplicated. But the point remains: parts of some genes
in the blood-clotting pathway are copies of parts of other genes.
See W.-H. Li and D. Graur, Fundamentals of Molecular Evolution
(Sunderland, MA: Sinauer, 1991) for a discussion of partial v.
complete gene duplicaion and the evolution of new gene function.
8 See J. A. Coyne, "God
in the Details," Nature 383 (1996): 227–28. Coyne
also emphasizes that Behe's theory is unfalsifiable: Since Behe
admits both evolution and design, proof that a pathway was built
gradually can't stump him. He can always claim that some other
pathway was designed.
9 Commentary (September
1996), p. 22.