Books & Culture (November/December 1996)

The Biochemical Challenge to Evolution
Exploring the elegance and irreducible complexity of biological systems at the molecular level


By Nancy Pearcey

Darwin's Black Box: The Biochemical Challenge to Evolution
By Michael Behe
Free Press
307pp.; $25

When light strikes the retina, a photon is absorbed by a molecule called cis-retinal, which causes it to change to trans-retinal." Such scientific jargon was unfamiliar terrain for a Washington, D.C., think tank, and the audience grew hushed.

"The change in retinal forces a corresponding change in the protein rhodopsin, which allows it to interact with another protein called transducin." Glances shot around the room as members of the audience furtively sought out others who were equally mystified.

"Transducin dissociates from a small molecule called GDP and binds to a different molecule called GTP, and this complex binds to a protein called phosphodiesterase. . . ." For several minutes the polysyllabic mysteries piled up, until finally embarrassed laughter broke out. But Michael Behe had made his point: Speaking to a group of educated nonscientists, he had walked them through the complex molecular interactions required for vision in a way they will never forget.

Behe's book, Darwin's Black Box, does the same thing for readers, painting a vivid picture of the cell's complexity. But his purpose is not simply to give a charming exposition of popular science, it is to challenge the Darwinist hegemony in biology.

Behe's thesis is that life depends on a host of molecular systems that are irreducibly complex, a phrase he introduces to indicate that such systems consist of several interlocking parts, all of which must be in place before they can function. And since Darwinian processes kick in only after there is minimal function, the origin of an irreducibly complex system is out of reach of standard Darwinian explanations.

As an analogy, Behe invokes the humble mousetrap: You cannot start with a wooden platform and catch a few mice, add a spring and catch a few more mice, add a hammer, and so on, with gradual improvement of function. To function at all, a mousetrap requires a minimum number of interacting parts assembled from the outset. By the same token, an irreducibly complex organic system like vision must be assembled all at once. It cannot appear gradually, piece by piece. But the heart of Darwinism is precisely such a gradualist scenario.

Darwin himself obligingly offered a way to falsify his theory, writing: "If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down." Behe's point is that the cell is chock full of molecular systems that could not have been formed by numerous, successive, slight modifications. Ergo, Darwinism has broken down.

To be fair to Darwin, he proposed his theory when scientists knew next to nothing about biochemistry. Living things were "black boxes," their inside workings a mystery. The cell itself was thought to be nothing more than a blob of jellylike protoplasm. It was easy to draw large-scale scenarios about fins gradually turning into legs, or legs into wings, since no one had a clue how limbs and organs work from the inside. As Behe writes, it is as though we asked how a stereo system is made and someone answered, "by plugging a set of speakers into an amplifier and adding a CD player, radio receiver, and tape deck."

Today that kind of answer won't cut it, Behe insists. The "black box" of the cell has been opened, and biologists are intimately familiar with its inside workings--its nuts and bolts. In terms of biological function, molecules are "the bedrock of nature," Behe writes. "Lower we cannot go." Any theory of the origin of living things must explain molecular systems.

Consider the origin of vision, a problem Darwin said made him shudder. Richard Dawkins, a contemporary Darwinist, brushes it off as no problem whatsoever: We simply begin with a light-sensitive spot, Dawkins writes, move to a group of cells cupped to focus light better, and continue through a graded series of infinitesimal improvements to a true lens. The sequence is quite persuasive on the surface. But what about under the surface? To function, Behe points out, even Dawkins's light-sensitive spot requires a cascade of factors, starting with cis-retinal and rhodopsin. About these complex molecular systems Dawkins is silent. And as for those cupped cells, dozens of proteins are involved in controlling shape and structure. About these complex proteins Dawkins says nary a word. It is the old strategy of telling us stereos are made by plugging in speakers and a CD player.

What we really want to know is whether Darwinism can explain how the speakers and CD players themselves were assembled. Behe maintains that it cannot, and offers two types of arguments. On one hand, he has combed the scientific literature and made the astonishing discovery that there are virtually no professional papers proposing detailed, testable hypotheses about the evolution of complex molecular structures. Explanations simply do not exist. And the reason they are nonexistent, Behe says, delivering his second punch, is that Darwinian explanations of irreducibly complex systems are exceedingly implausible.

At the heart of the book are five chapters that drive the point home by describing different types of irreducible complexity. Some systems consist of interdependent parts that must be assembled all at once, like our mousetrap. An example is the hairlike cilium, which functions like an oar and requires the interplay of more than 200 different proteins. Other systems are sequential, like a Rube Goldberg machine. An example is the blood-clotting mechanism, in which numerous steps are exquisitely timed by a series of catalysts to ensure that blood clots at the site of a wound and at no other place or time. Still other systems depend on delicate recognition signals. Certain molecules in the cell act as transport vessels that must recognize the right "pick-up" and "drop-off" zones, as well as the right materials to carry. Readers who follow Behe's discussion example by example will find it hard not to agree that the complexity of these molecular systems is indeed irreducible--that they could not arise by any step-by-step, Darwinian process.

What alternative does Behe offer? Intelligent design theory. Structures that consist of interacting, co-adapted parts, he argues, are evidence of a purposeful, intelligent agent. At this point, many readers may balk, objecting that science is not equipped to deal with anything outside nature. To which Behe replies: Catch up with the late-twentieth century. It was 60 years ago that the Big Bang theory was proposed, and cosmologists had to confront the idea of an ultimate origin of the universe-no matter how philosophically "repugnant" (A. S. Eddington's word) they found that idea because of its implication of a personal creator. Now it is biology's turn to recognize that its data may likewise have discomfiting implications.

Behe is careful to limit his own discussion to that data and its immediate implications. Thus he denies that we can reason from design in nature to the existence of the Christian God. All we can say is that a natural object exhibits the characteristics of intelligent manufacture--no more. In Behe's words, "inferences to design do not require that we have a candidate for the role of designer." We might select a candidate based on philosophical or theological grounds but not on scientific grounds.

Behe's tight focus on scientific data means he treats historical and philosophical issues only gingerly. Except for brief (though illuminating) discussions of Paley and Socrates, we hear little about the history of the concept of design. No mention is made of Georges Cuvier, who in the nineteenth century developed a similar notion of irreducible complexity (calling it "the correlation of parts"). Nor is there any discussion of contemporary proponents of design theory, such as Michael Denton (Evolution: A Theory in Crisis ) or Thaxton, Bradley, and Olsen (The Mystery of Life's Origin ).

This narrow lens may be frustrating to some readers, and yet adopting it was probably good strategy. Behe is an associate professor of biochemistry at Lehigh University, and he stays squarely within his own field of expertise. He crafts one basic argument, and he crafts it well. Even secular scientists grant him grudging praise. Alan Wolffe at the National Institutes of Health does not share Behe's notion of intelligent design, yet he praises the quality of the book's argument, saying that it "exposes our lack of knowledge concerning biochemical evolution." Robert Shapiro at New York University, author of Origins: A Skeptic's Guide to the Creation of Life on Earth, says Behe "demonstrates clearly that current scientific theories cannot tell us the way in which this complexity [of life] arose from non-living matter."

Despite the clarity of Behe's writing, a few points may leave readers puzzled. Is Behe a creationist? He explicitly eschews the term. Though a Roman Catholic, he accepted Darwinism for many years without sensing any contradiction with his faith, and still accepts the idea of common descent. The conclusion of design is drawn from scientific data, he insists, and "not from sacred books or sectarian beliefs." It is significant that the book came out from a major New York publisher, not a religious publishing house. Yet Behe may protest a bit too much. He rejects the label "creationist" only by limiting the term narrowly to those who insist on a young Earth (about 10,000 years old)--thus disqualifying a host of people who consider themselves creationists. Similarly, Behe accepts common descent only by giving that term a highly atypical definition. His idea is that an original one-celled organism contained the information for all subsequent biological development, which advanced through multiple, coordinated changes in large, sudden leaps (akin to Richard Goldschmidt's "hopeful monster" theory except that the monsters appear not by luck but through the unfolding of an implicit design).

Behe's book makes a powerful contribution to the literature on the Darwin controversy. The black box has been opened. Biologists had better get ready to face the implications of what they find there.

Nancy Pearcey is fellow and political director of the Wilberforce Forum and coauthor, with Charles Thaxton, of The Soul of Science (Crossway).