Signs of design: is there purpose in evolution?

BECAUSE I AM a biologist, evolution is at the core of virtually everything I think about. Like most of my colleagues, I've kept an eye on the emerging "intelligent design" movement. Unlike most of my colleagues, however, I don't see ID as a threat to biology, public education or the ideals of the republic. To the contrary, what worries me more is the way that many of my colleagues have responded to the challenge.

ID proponents claim that Darwinism is insufficient to explain the origin and evolution of life on Earth. All is better explained, they say, if there is some kind of designing intelligence guiding things. These assertions are based on two core ideas. The first is essentially a scientific theory of miracles that is the brainchild of philosopher and mathematician William Dembski, one of ID's leading intellectual lights. According to Dembski, one can use rules of probability and information theory to construct "explanatory filters" that can objectively distinguish between purely natural phenomena that come about on their own and phenomena that require some kind of intelligent guidance--a miracle, in a word. Applying an explanatory filter to, say, the origin of life reveals that the probability that life arose by chance is infinitesimal. This in itself is not a particularly novel or controversial idea--no biologist I know would disagree. But Dembski parts company with the rest of us when he insists that a designing intelligence is the only agency that could bring such an improbable event to pass. What heats people up, of course, is that Dembski's "designing intelligence" strikes many as code for "God."

The second core idea comes from microbiologist Michael Behe, who is another of ID's leading lights. He asserts that living systems exhibit a sort of "irreducible complexity" that cannot be derived from the piecemeal evolution that Darwinism demands. The poster child for this argument is the bacterial flagellum, a whiplike device that bacteria use to propel themselves around their environment. This remarkable contrivance, which resembles an electric motor, is built from protein parts and will work only when all the parts are assembled into the complex whole--and this is why Behe calls its complexity irreducible. Whether the flagellum actually is irreducibly complex is questionable: scientists have proposed reasonable models for how its design could have emerged via piecemeal evolution.

Nevertheless, Behe considers irreducible complexity to be proof positive of a designing intelligence at work: how could the flagellum have developed by natural selection if none of its elements by themselves would have made the organism's predecessor more fit to survive? Behe claims that many other attributes of living systems, including the complicated structure of genomes, mechanisms for gene replication, and complex metabolic pathways in cells, are likewise irreducibly complex. What stirs the pot is ID's claim that all this irreducible complexity constitutes a rhetorical dagger pointed at the heart of Darwinism.

If all this sounds familiar, it should: it is essentially natural theology and the argument from design dressed up in modern clothes--William Paley equipped with a computer and electron microscope. Looked at in this way, ID seems not so much like the radical alternative to Darwinism that it claims to be, and more like nostalgia for the Platonic tradition in natural history that prevailed prior to Darwin.

The nostalgia is puzzling: for centuries, the Platonic tradition tied natural history into knots, with some of the most intractable tangles woven around the nature of species and the meaning of the apparent design that abounds in the living world. In a single decisive stroke, Darwin cut a wide path through this Platonic morass with a simple and, most important, reasonable natural explanation for why species exist and why they exist in such marvelous diversity and complexity. To extend Richard Dawkins's famous quip that Darwin made it possible to be an intellectually fulfilled atheist, so too did Darwin make it difficult to be an intellectually credible Platonist.

Nevertheless, ID is as popular as it is controversial, and Platonic nostalgia is not enough to explain why. Something deeper is obviously at play.

TO MOST PEOPLE who contemplate the natural world, it seems self-evident that the world is a designed place. Despite its many difficulties, the Platonic tradition endured because it offered a satisfying explanation for why: the world reflects God's purposeful design for creation. In dethroning the Platonic tradition, Darwin seemed to take that purpose away, and this has obviously been a difficult pill for many to swallow. It's not so clear, however, that Darwin did divorce design and purpose so decisively from the living world. Indeed, to claim that he did is to misread the history of Darwinism.

Consider, for example, the bedrock concept of Darwinian fitness. Natural selection operates because "fit" individuals are more fecund than "unfit" individuals. This should, over time, produce populations of fitter creatures, even though there is no purpose at work here, no striving for perfection. However, a problem lurks in this seemingly simple explanation. For a scientific idea to be credible, there must at least be the possibility that one can show it to be incorrect. Darwin ran into early difficulty on this score because the conventional depiction of fitness cannot be false--fecundity is fitness, and fitness is fecundity. To Darwin's early critics, a veritable fountain of doubt gushed from this tautology at the heart of his theory.