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
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