By George Johnson
FOR the squirming jurors held captive in Judge Lance A. Ito's Los Angeles courtroom, the last couple of weeks of DNA testimony must seem like the worst possible visitation of a well-known recurrent nightmare: It's the last week of the semester and suddenly you remember the science class you forgot you signed up for and never thought to attend. Too late to drop it now. In a vast, silent hall, you stare at the final exam with its sickening thicket of meaningless symbols and equations. Your head swimming with the nausea of incomprehension, you run for the exit, but the security guards stop you at the door.
You're being asked to comprehend the incomprehensible, and to compound the horror, you learn it is not your grade point average at stake, but whether a man will be convicted of murder.
With its charts of copulating nucleotides and numbing presentations about introns, exons and the differences between the polymerase chain reaction and restriction fragment length polymorphism, the O. J. Simpson trial has taken on the tedious, didactic flavor of every bad science class you were forced to sit through. But as unwanted as this crash course in molecular genetics might be, perhaps the jurors are being exposed subliminally to a deeper, more disquieting lesson -- one about the very nature of knowledge, scientific, legal and otherwise.
Throughout the ordeal, courtroom commentators have agonized over whether jurors without advanced degrees, much less college diplomas, can grasp the molecular intricacies well enough to make a reasoned determination of Mr. Simpson's fate. But perhaps the confused expressions on the jurors' faces betrays a more profound incomprehension -- a realization that even in science, truth is always tentative. Even in science, the facts are inevitably open to interpretation.
The Next Expert
If the trial were truly to plumb the depths of the scientific issues at play in Judge Ito's courtroom, the testimony of DNA experts would have to be followed by testimony from some of the philosophers, living and dead, who have contemplated these issues. And so, as if the trial were not already long enough, imagine that the defense has called to the stand a surprise witness, the renowned philosopher of science Sir Karl Popper, who died last year.
"You may think," he declares, "that the prosecution has proved beyond a shadow of a doubt that the DNA in the blood on the gate at the crime scene is Mr. Simpson's, or that the DNA in the bloody sock and glove is a mixture of O.J.'s and the unfortunate victims'. But I say the prosecution is being naive about the scientific method."
"A scientist begins," Dr. Popper reminds the jury, "by formulating a hypothesis -- the idea, say, that the moon circles the earth, the stars are powered by hydrogen fusion, the blood on the sidewalk is Mr. Simpson's. Then the scientist designs an experiment to test what has been supposed.
"However," Dr. Popper says, raising his voice just enough to strip the glaze from the jurors' eyes, "a hypothesis can only be negated, never proved."
The prosecution groans. Sir Karl is trying to snow the jury with the old Problem of Induction.
"There is a story we philosophers tell," Dr. Popper continues. "No matter how many white swans you see, you are not entitled to conclude that all swans are white. A black one may be lurking around the corner."
One of the lawyers from the defense team raises his brow and asks Dr. Popper pointedly: "Are you saying that these blood samples on which the prosecution's case hinges are like the white swans?"
"That's correct," Sir Karl says.
"And no matter how many labs match blood samples to Mr. Simpson or to the victims, one can never know if a fourth lab or a hundredth will come back with a negative result?" "All it takes is one black swan," Dr. Popper says. "And since there can always be one more test, the prosecution can never 'prove' its point. That's the nature of scientific induction. No hypothesis can be verified, it can only resist falsification."
At this point, the prosecution, having anticipated Dr. Popper's philosophical dodge, calls its own expert witness, the philosopher of science W.V.O. Quine.
"Don't be so sure about the devastating effect of that hypothetical black swan," Dr. Quine warns the jury. "Popper may tell you that the prosecution's case is always on the verge of being proved wrong. But there is something he is leaving out: The Problem of the Auxiliary Hypothesis."
He pauses for effect.
"Even if you do see a black swan," he says, "that doesn't necessarily mean that your hypothesis about swan whiteness has been refuted. Perhaps this black swan is really white, but a disease of some sort blackened its feathers. Perhaps it fell into a coal bin. Perhaps through a momentary neurological defect -- a misfiring neuron -- your visual system incorrectly registered the color. And even if a hundred people say they saw the black swan, it's possible that an errant electromagnetic field somehow distorted their brain waves."
The prosecutor, sensing that the testimony is veering toward the abstruse, steers Dr. Quine to the point. "So you're saying that even if the defense conjured up that imaginary negative blood test, this would not necessarily overturn the prosecution's hypothesis about the blood on the sock."
"That's right," Dr. Quine says. "A negative experimental result cannot be said to overturn a specific hypothesis, whether it's about swans or bloodstains. You can always explain away the outcome with an auxiliary hypothesis."
"You mean somebody might have botched the test?" the prosecutor says.
"Well, yes," Dr. Quine replies. "But I'm talking about something far more subtle than contamination or clumsiness. Every experiment is embedded in a vast network of assumptions, beliefs, theories."
"Does that mean," the prosecutor asks, "that if the result is negative, the fault could lie anywhere within this sprawling spider web of knowledge?" He looks aghast. "So, Popper just told us that a hypothesis can never be proven true, and now you're saying that a hypothesis can never be proven false!"
The jury's hush is broken by Judge Ito. "What next?" he barks. "Will we call a deconstructionist to the stand to argue about postmodern justice?" Then he orders the jury to wipe from their minds all this philosophical obfuscation. "Scientists and philosophers might be troubled by these objections," he says. "But in a trial, we must tolerate a lower standard of evidence: 'proof' beyond a reasonable doubt."
What No One Saw
Sir Karl and Dr. Quine exchange knowing glances, as if to say, "If only it were so simple."
Like the murders of Nicole Brown Simpson and Ronald L. Goldman, so many of the universe's pivotal events have no eyewitnesses -- the big bang, the beginning of life on earth and its subsequent unfolding: Not one of these events had an eyewitness. In trying to understand them, we rely on circumstantial evidence that is always open to debate and interpretation. And like a scientific hypothesis, a conviction can always be overturned.
But there is one gnawing difference. No one can know first hand what actually happened when the universe violently burst into life. Presumably there is one person who knows whether O. J. Simpson committed the murder. And that is O. J. Simpson.
Science in the late 20th century may be able to peer into a man's DNA and match it to a spot of blood on a sidewalk. Will science in the late 21st century be able to peer into his neurons and read the memories imprinted there? Can it conceivably wipe away all the epistemological troubles and prove beyond a doubt, reasonable or otherwise, that someone committed a crime?
Probably not. The neural data, like the DNA tests, would also be subject to interpretation. They too are records, not events. If anything is certain it is that in the search for truth we are always one step removed.
GRAPHIC: Photo: Strands of DNA: evidence or enigma? (pg.1); The old Problem of Induction again: Is the DNA evidence as transparent as it looks? (Agence France-Presse)(pg.16) LANGUAGE: ENGLISH