In 2004, the science department of the Dover Area High School in Eastern Pennsylvania met to select a new textbook for its general biology course.

The choice was a widely used Prentice Hall text by Brown University professor Kenneth R. Miller and Joseph S. Levine.

The selection process seemed unremarkable until one of the Dover school board members complained that the choice was "laced with Darwinism from beginning to end" and offered an alternative that included "Of Pandas and People," a schoolbook devised by advocates of "intelligent design."

Mainstream science rejects ID's claim of scientific legitimacy because it introduces an entity called the intelligent designer whose powers go beyond nature.

Though ID advocates, such as the researchers of the Discovery Institute, explicitly distinguish that designer from a deity, their approach still looked enough like religion to prompt a group of 11 Dover parents to file a federal lawsuit.

The plaintiffs, led by Tammy Kitzmiller, alleged that the board had violated their First Amendment rights by establishing a particular religious doctrine as part of the school's curriculum.

With that, a local skirmish over Darwin's theory erupted into Kitzmiller vs. Dover, a full-fledged legal battle between advocates of ID and evolution. Judge John E. Jones III, a conservative appointed by President George W. Bush, presided.

Miller does not tell the full story of that trial. Rather, his purpose is to present its implications, drawing on both his broad perspective as a leading biology educator and his experience as the plaintiffs' opening and most important witness.

He draws his title from a brief encounter in a courtroom from an earlier case, where "even a whisper can catch your attention, especially one that comes right at you with a smile and a wink."

" 'Only a theory,' she said, shaking her head just enough to get my attention as I walked past her," Miller continues. 'It's only a theory -- and we're gonna win.' Her smile was genuine, and its certainty was unmistakable."

She didn't win in that trial, as Jones recognized that ID was old-fashioned creationism in a fancy suit, but Miller and his courtroom antagonist both know that the uniquely American cultural war over evolution will continue.

That prospect worries him, especially as he ponders the goals and strategies of the ID movement.

Under the guise of proposing "irreducible complexity" as a competing hypothesis to Darwinism, ID advocates set out to demonstrate scientifically that an entity they describe as the intelligent designer must exist. The designer is not necessarily divine (although they won't argue against that), but he, she or it clearly must operate beyond the natural realm.

The problem with this approach is that it works only if science is redefined to include the "non-natural," a term ID advocates use to avoid "supernatural." The tactic, if successful, not only overturns evolution but also shreds the fabric of natural science itself.

Why should the designer only work in biology? Why invoke astrophysics and 13.7 billion years of history to explain the universe? Why invoke 4.5 billion years of solar system development to create the kind of planet on which the designer could bring a long sequence of ecologies into existence, only to have them replaced by other ecologies until one eventually emerges in which humans dominate?

Despite all their efforts to prove that irreducibly complex units exist, ID researchers have been foiled by nature itself. Miller describes scientific research that has systematically demolished ID's most cherished claim.

The advocates have been forced to go back to the drawing board, but they are not giving up. Miller worries about what damage their continuing assault may produce.

Yet he expresses confidence in the unique American system that encourages challenges to the established order. It is the source of the legendary American individuality and self-sufficiency that economic conservatives tout as the engine that drives our progress.

That system is economic evolution by natural selection, and it happens without a designer's intervention. Why shouldn't life on Earth, or any other planet, operate in the same way?