Science fiction: if we fail to fire up our "little grey cells," following the evidence is likely to lead to forensic fundamentalism.

DON'T LOOK NOW, BUT JERRY BRUCKHEIMER'S hit show CSI: Crime Scene Investigation is replicating itself faster than the bugs Gil Grissom (William Petersen) finds under victims' toenails. In the beginning Grissom and his science geeks took on the villains of Las Vegas. Then Horatio Caine (David Caruso) unleashed his microbe hunters on the felons of Miami. Now Mac Taylor (Gary Sinise) and friends are looking for worms in the Big Apple. Maybe next season Mickey and Goofy will be taking on Cruella DeVil's DNA in CSI: Disneyland.

A lot of adolescent males (of any age) are going to like shows about Las Vegas or Miami, places where showgirls and other women don't wear much clothing. Many of the same teens will also be attracted to shows with plenty of high-tech gore--worms and bugs crawling out of open wounds and all sorts of seeping and pooling body fluids. Guh-ross! As long as there are high school boys who throng to The O.C. and Night of the Living Dead, Bruckheimer shouldn't have any problems recruiting viewers for CSI.

But the fundamental appeal of CSI runs deeper than bikinis or bullet holes. Grissom and his Miami and New York knock-offs are overgrown science geeks preaching the gospel of DNA in a world mired in confusion, ambiguity, and uncertainty. Armed with microscopes, scanners, and an encyclopedic knowledge, these lab-coated cops are not just waging war on crime and drugs, they are declaring victory over ignorance, error, and failure.

Three nights a week these phlegmatic nerds sort through the mess and mayhem of murder, undistracted and undeterred by lying witnesses or dead-end leads. "Follow the evidence," Grissom tells his bloodhound investigators. "It's the only thing that can't lie." And at the end of their spectrometer is always the unique spoor of their killer, the incontrovertible evidence of his guilt, as well as irrefutable proof of the success and surety of our scientific know-how. Like the mythic Canadian Mountie, the CSI brainiacs always get their man--because in the world of fingerprint and DNA analysis there is no room for interpretation, ambiguity, or error.

THE POPULARITY OF THE GEEK DETECTIVE IS NOTHING NEW. Arthur Conan Doyle gave us Sherlock Holmes, whose 221 B Baker apartment was regularly filled with the smoke and smells of some experiment and whose desk always had a stack of obscure but relevant scientific monographs. Like Grissom, Holmes loved putting his crime scene evidence under the magnifying glass, checking out footprints, soil samples, and the wear pattern on a pair of boots.

Agatha Christie's master detective, Hercule Poirot, did not share Holmes' penchant for lab work, but he, too, had limitless faith in "the little grey cells" of his very clever brain and was supremely confident in the ability of human intelligence to solve life's most daunting mysteries. So, too, Rex Stout's Nero Wolfe relied solely on his brain power to solve the crimes that made their way to his Bronx brownstone.

Still it seems ironic that shows like CSI are so popular at a time when our ability to discover the truth of the matter seems so frail. Perhaps we cling to the unshakeable faith of these nerdy investigators because we want to live in a world where we base our judgments on clear, certain, and correct data. Maybe we love these shows because we want to inhabit a moral universe where the difference between guilt and innocence and right and wrong is a matter of black and white, a question of a negative or positive lab result.

But our world makes the faith of the CSI nerds a lie.

In spite of all the scientific evidence gathered by real-world crime sleuths, most crimes go unpunished. In Race to Incarcerate (New Press) and Crime and Punishment in America (Owl Books) Marc Mauer and Elliott Currie report that the majority of crimes, violent and otherwise, do not even come to the attention of the police or courts and of those that do only a small fraction result in conviction and punishment.

In 1994 there were approximately 3.9 million victimizations for violent offenses (rape, robbery, aggravated assault, and homicide), 1.9 million of which were reported to the police, leading to 779,000 arrests, 143,000 felony convictions, and 117,000 incarcerations.

In our world even when we do get our man, we often make grave errors. In 2003 George Ryan, the outgoing governor of Illinois, commuted more than 160 death sentences when he learned that 13 inmates had been wrongly convicted and that research showed racial bias skewed convictions and sentencing rates.

There may be no bias or error in the hearts--or lab results--of TV scientists but there is plenty of it in real life. Death Penalty Information Center attorney Richard Dieter notes that a study of death penalty cases from 1973 to 1995 revealed that "in more than two thirds of the cases mistakes were made in the [original] trial that were so serious the person should not have been convicted."

And in our world we sometimes go to war based on bad information. Two years ago the White House assured the United Nations, Congress, and the American people that it had incontrovertible evidence of Iraq's weapons of mass destruction. Last October, with more than 18,000 Iraqis dead and more than 1,000 American soldiers killed, our government's leading weapons inspector acknowledged that this information was bogus. Iraq had no weapons of mass destruction. Saddam Hussein had destroyed his nation's illicit weapons programs more than a decade before and had not made any concerted effort to restart these programs.

The smartest, richest, best-equipped intelligence community in the world had gotten it horribly, catastrophically, wrong--in no small part because the ambiguous and uncertain information we had was politicized to create the result our leaders wanted.

During Vietnam another generation of Americans placed their faith in the number crunching of Secretary of Defense Robert S. McNamara. For years Kennedy and Johnson's wunder-kind produced charts and tallies that showed how clearly we were winning the war. Only later did we discover that McNamara had cooked the books and that the government had hidden much of the truth from us. Only later did we learn that evidence has to be questioned, interpreted, and evaluated, and that if the evidence, as CSI's Grissom proclaims, does not lie, it also does not tell the truth on its own.

JESUS WARNED HIS DISCIPLES THAT IT IS easy to see the speck (or the WMDs) in our neighbor's eye but hard to see the plank in our own. A teacher once told me 90 percent of what we see is behind our eyes, not in front of them--meaning that the interpretive lenses through which we see and judge the world have a much greater impact on us than what is actually in front of our eyes.

Shows like CSI are a problem if they support a fundamentalist approach to "the evidence," a belief that we can just read the information we find without interpreting or analyzing it. In the real world, information and evidence are ambiguous, incomplete, and almost always delivered by people (like ourselves) with agendas and biases.

Before we make judgments based on that evidence, we need to have a sense of our own planks or biases, we need to fill in the blanks with guesses and judgments, and we need to interpret and analyze all the information we have, taking responsibility for having made a frail, fallible decision.

Fundamentalism, whether biblical, theological, or scientific, is a desire to escape the responsibility of making hard choices with limited information. If we believe we can avoid the hard work of thinking or the pain of making mistakes by quoting scripture, the pope, or the results of a lab test, we are sadly mistaken. Even if Jerry Bruckheimer brings a CSI franchise to every town and village, there will still be no place we can hide from the human task of making decisions that could turn out to be wrong.

PATRICK MCCORMICK, professor of Christian ethics at Gonzaga University in Spokane, Washington.