"Boston Review" December-January 1996-97

Darwin v. Intelligent Design (Again)
The latest attack on evolution is cleverly argued, biologically
informed-and wrong.

H. Allen Orr

Review: 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.
-Wittgenstein1

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 agent.

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 a hypothesis"4).

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.

Irreducible Complexity

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 dizzying complexity.

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

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."

Reducible Complexity

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 complexity.

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 be
required.

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 get built.

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.

Irreducible Confusion

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 about evolution.

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 Gomorah: 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 not reversible.

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.

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