Darwin's Black Box: The Biochemical Challenge to Evolution

Public Interest, Wntr, 1997 by Stephen M. Barr

Of the many proofs of the existence of God, perhaps the one that makes the most direct appeal to our intuition and common sense is the Argument from Design. Writing in 1840, Macaulay observed:

A philosopher of the present day ... has before him the same evidences of design in the structure of the universe which the early Greeks had, ... for the discoveries of modern astronomers and anatomists have really added nothing to the force of that argument which a reflective mind finds in every beast, bird, insect, fish, leaf, flower, and shell.

But if from the time of the early Greeks until Macaulay's day, things were quiet in this particular branch of natural theology, they have heated up since then. For, just 19 years after Macaulay wrote those words, Darwin published The Origin of Species. Now, not only the discoveries of astronomers and anatomists but those of researchers in every field, from information theory to molecular biology, are marshaled to attack (and to defend) the Argument from Design.

Many people suppose that Darwin destroyed the Argument from Design once and for all - at least in biology. But this is not so, as Michael J. Behe convincingly argues in his important new book Darwin's Black Box: The Biochemical Challenge to Evolution.(*) As a molecular biologist at Lehigh University, Behe writes with authority about such things as ribosomes and polypeptides. But he writes for the layman, managing to make the arcana of his field not only very clear but also lively and entertaining. And, from his redoubt in the inhospitable terrain of biochemistry, he has issued a formidable challenge to the current version of evolutionary theory.

There is no denying the brilliance of Darwin's insights. Before he proposed the idea of natural selection, no one had ever found a way to explain the apparent "purpose" of biological structures without invoking Design. In fact, no one seems to have dreamed that there could be some other explanation. Darwin did, even for something as intricate as the human eye. It is obvious that a random mutation of the genes that could produce an eye would be absurdly improbable. However, there is an answer in Darwinian theory to the problem of complexity. A large change can be built up through a sequence of "small" (in the sense of probabilistically achievable) steps, each of which need only confer some incremental selective advantage on the organism. This is the idea of Darwinian gradualism. Darwin himself proposed a very plausible sequence of steps that might have led to the human eye.

Behe, significantly, does not reject all of Darwin in his effort to rescue the biological Argument from Design. All that is logically required is to find some - maybe only a few - convincing examples of complex biological systems that cannot be explained by Darwinian gradualism. Darwinism (or neo-Darwinism) does not have to be wrong, just incomplete. As Behe notes, "The production of some improvements in organisms by mutation and natural selection - by evolution - is quite consistent with intelligent design theory."

Thus Behe, unlike many critics of Darwin, is willing to admit a large role for natural selection in evolution - even, it seems, in "macroevolution" (roughly speaking, the production of entirely new species or types). But he finds certain examples in biology - called by him systems of "irreducible complexity" - which he argues natural selection is powerless to explain. These are systems that, in order to function at all, require the coordinated activity of many parts and that consequently can only arise all at once, in an improbable "big" step. The elegant paradox at the heart of Behe's book is that the place to look for these big steps is at the level of the very small.

As Behe emphasizes, the real action of life takes place in the cell, at the molecular level. Until recent decades, the cell was a "black box," which evolutionary biologists could assume would produce the postulated mutations. But to know whether these mutations are really "small" in the required sense, one has to know how they might be produced genetically - and that is a question of molecular biology.

Due to the patient and clever work of generations of scientists, this black box has been opened. And one finds that, as life is examined at smaller and smaller scales, the structures and processes uncovered seem not simpler and more elementary but increasingly complicated. Indeed, what goes on in the simplest cell is of staggering complexity.

Behe focuses on five molecular systems of "irreducible complexity": the cilia of cells, the chemistry of vision in the retina, the blood-clotting system, the system by which new enzymes are manufactured and transported to the sites in the cell where they are needed, and the immune system. It is an important point that all these systems are fundamental and widespread in the animal kingdom and are necessary in particular for the human species.

As anyone who has seen a good magic show knows, sometimes a thing that seems impossible turns out to be rather simple once you know how it is done. Moreover, one can imagine cases where a system that appears, at first sight, to be "irreducibly complex" is not so. An example that occurs to me is a free-standing Roman arch, which would topple if any single stone were removed. Yet one can build up such a structure one stone at a time by using scaffolding in the intermediate stages of construction. Even though I have tried, with thoughts like these, to maintain an attitude of cautious skepticism regarding Behe's claims, I cannot help wondering how on earth such systems as he describes could possibly have evolved in a gradualistic manner.