Darwin Under the Microscope
New York Times Op Ed
October 29, 1996
by Michael Behe, associate professor of biochemistry at Lehigh University,
is the author of "Darwins's Black Box, The Biochemical Challenge to
Evolution.
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Pope John Paul II's statement last week that evolution is "more than just a
theory" is old news to a Roman Catholic scientist like myself.
I grew up in a Catholic family and have always believed in God. But
beginning in parochial school I was taught that He could use natural
processes to produce life. Contrary to conventional wisdom, religion has
make room for science for a long time. But as biology uncovers startling
complexity in life, the question becomes, can science make room for
religion?
In his statement, the Pope was careful to point out that it is better to
talk about "theories of evolution" rather than a single theory. The
distinction is crucial. Indeed, until I completed my doctoral studies in
biochemistry, I believed that Darwin's mechanism - random mutation paired
with natural selection - was the correct explanation for the diversity of
life. Yet I now find that theory incomplete.
In fact, the complex design of the cell has provoked me to stake out a
distinctly minority view among scientists on the question of what caused
evolution. I believe that Darwin's mechanism for evolution doesn't explain
much of what is seen under a microscope. Cells are simply too complex to
have evolved randomly; intelligence was required to produce them.
I want to be explicit about what I am, and am not, questioning. The word
"evolution" carries many associations. Usually it means common descent -
the idea that all organisms living and dead are related by common ancestry.
I have no quarrel with the idea of common descent, and continue to think it
explains similarities among species. By itself, however, common descent
doesn't explain the vast differences among species.
That's where Darwin's mechanism comes in. "Evolution" also sometimes
implies that random mutation and natural selection powered the changes in
life. The idea is that just by chance an animal was born that was slightly
faster or stronger than its siblings. Its descendants inherited the change
and eventually won the contest of survival over the descendants of other
members of the species. Over time, repetition of the process resulted in
great changes - and, indeed, wholly different animals.
That's the theory. A practical difficulty, however, is that one can't test
the theory from fossils. To really test the theory, one has to observe
contemporary change in the wild, in the laboratory or at least reconstruct
a detailed pathway that might have led to a certain adaptation.
Darwinian theory successfully accounts for a variety of modern changes.
Scientists have shown that the average beak size of Galapagos finches
changed in response to altered weather patterns. Likewise, the ratio of
dark- to light-colored moths in England shifted when pollution make
light-colored moths more visible to predators. Mutant bacteria survive when
they become resistant to antibiotics. These are all clear examples of
natural selection in action.
But these examples involve only one or a few mutations, and the mutant
organism is not much different from its ancestor. Yet to account for all of
life, a series of mutations would have to produce very different types of
creatures. That has not yet been demonstrated.
Darwin's theory encounters its greatest difficulties when it comes to
explaining the development of the cell. Many cellular systems are what I
term "irreducibly complex." That means the system needs several components
before it can work properly. An everyday example of irreducible complexity
is a mousetrap, built of several pieces (platform, hammer, spring and so
on). Such a system probably cannot be put together in a Darwinian manner,
gradually improving its function. You can't catch a mouse with just the
platform and then catch a few more by adding the spring. All the pieces
have to be in place before you catch any mice.
An example of an irreducibly complex cellular system is the bacterial
flagellum: a rotary propeller, powered by a flow of acid, that bacteria use
to swim. The flagellum requires a number of parts before it works - a
rotor, stator and motor. Furthermore, genetic studies have shown that about
40 different kinds of proteins are needed to produce a working flagellum.
The intracellular transport system is also quite complex. Plant and animal
cells are divided into many discrete compartments; supplies, including
enzymes and proteins, have to be shipped between these compartments. Some
supplies are packaged into molecular trucks, and each truck has a key that
will fit only the lock of its particular cellular destination. Other
proteins act as loading docks, opening the truck and letting the contents
into the destination compartment.
Many other examples could be cited. The bottom line is that the cell - the
very basis of life - is staggeringly complex. But doesn't science already
have answers, or partial answers, for how these systems originated? No. As
James Shapiro, a biochemist at the University of Chicago, wrote, "There are
no detailed Darwinian accounts for the evolution of any fundamental
biochemical or cellular system, only a variety of wishful speculations."
A few scientists have suggested non-Darwinian theories to account for the
cell, but I don's find them persuasive. Instead, I think that the complex
systems were designed - purposely arranged by an intelligent agent.
Whenever we see interactive systems (such as a mouse trap) in the everyday
world, we assume that they are the products of intelligent activity. We
should extend the reasoning to cellular systems. We know of no other
mechanism, including Darwin's, which produces such complexity. Only
intelligence does.
Of course, I could be proved wrong. If someone demonstrated that, say, a
type of bacteria without a flagellum could gradually produce such a system,
or produce any new, comparably complex structure, my idea would be neatly
disproved. But I don't expect that to happen.
Intelligent design may mean that the ultimate explanation for life is
beyond scientific explanation. That assessment is premature. But even if it
is true, I would not be troubled. I don't want the best scientific
explanation for the origins of life; I want the correct explanation.
Pope John Paul spoke of "theories of evolution." Right now it looks as if
one of those theories involves intelligent design.
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Brian Harper | "If you don't understand
Associate Professor | something and want to
Applied Mechanics | sound profound, use the
The Ohio State University | word 'entropy'"
| -- Morrowitz
Bastion for the naturalistic |
rulers of science |