Darwin Under the Microscope

Michael J. Behe
The New York Times
October 29, 1996
Print ArticlePope 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 made 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 made 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't 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 mousetrap) 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 II spoke of "theories of evolution." Right now it looks as if one of those theories involves intelligent design.

Michael Behe is a Professor at Lehigh University and the author of the critically acclaimed Darwin's Black Box.