When they set out to banish food cancer risks, scientists thought their job was clear: Find food ingredients that can cause cancer and ban them.
But reality has proven far more complicated than the Food and Drug Administration scientists expected when they started work more than 30 years ago.
The researchers found that a cornucopia of natural food components could be called cancer-causers if they were extracted from their source and fed to rats and mice in high doses, as is done to test synthetic food additives.
”The tests were originally designed to eliminate single carcinogens from the diet, when it was thought that that was what caused cancer,” said Robert Scheuplein, FDA director of toxicology sciences.
So after three decades of testing, what the FDA has learned is that its initial premise was wrong. The agency said last week that our food is replete with so many natural carcinogens that it`s impossible to identify and remove them all.
Scheuplein said that more than 98 percent of the cancer risk represented by food comes from natural components, and only 2 percent from artificial sources.
It is startling to learn that eating nutritious, healthful foods may pose some cancer risk, however minuscule. But don`t be too concerned. Among the experts discussing the issue, none has changed personal eating habits based on the discoveries.
But the FDA revelation, part of the program at the annual meeting in New Orleans of the American Association for the Advancement of Science, is only a piece of the picture of modern science that emerges.
Indeed, research snippets presented from disparate fields, when taken together, suggest a conclusion even more basic to a society underpinned by advanced technology: Scientists know less than they, or we, believe they know. The true summation of scientific discovery isn`t how much we`ve learned about nature, but rather a better understanding of how incredibly complex nature is. Scientists, like any humans, have their foibles, and they may want to oversimplify reality as quickly as the next person.
But nature guards its secrets jealously, and in science, the simplest questions generally lead not to simple answers, but to more complex questions. People who rush to embrace food fads or otherwise alter their lives because of advice branded as scientific fail to keep in mind that human understanding of nature is still tentative and subject to frequent revision.
The anti-cholesterol campaign and oat-bran bandwagon show what happens when people forget that scientific ”facts” have a history of changing with time.
A few other reports from the meeting, on subjects ranging from pigeons to pulsars, demonstrate scientific limitations.
In their quest to learn how pigeons fly home when released in strange territory hundreds of miles away, scientists have watched the birds with binoculars and followed them in airplanes. Researchers also have put frosted contact lenses on the birds` eyes, metal helmets on their heads, magnets on their backs and odor suppressants in their nostrils, trying to stymie the homing instinct.
Italian ornithologists find they can easily confuse pigeons by anesthetizing their nostrils to block the birds` ability to smell. This persuaded them the birds rely on mental odor maps to find home.
German biologists, however, found no difference in their birds` homing abilities when smell was blocked. They scoffed at Italian theories until someone noted that the German pigeons were raised in a courtyard where walls blocked breezes bringing aromas of the surrounding countryside.
German flocks raised in an elevated roost open to country breezes produced some birds that were confused when they couldn`t smell, but also some birds whose homing wasn`t affected.
American biologists found that pigeons raised at Cornell University`s roost in Ithaca, N.Y., were sometimes confused by losing their smell. But the birds almost always get lost if released from a fire tower on Jersey Hill several miles west of Ithaca, said Charles Walcott, a Cornell biologist.
Birds raised at other roosts have no trouble when released from Jersey Hill, nor do offspring of Ithaca birds raised at other roosts, Walcott said. Despite 20 years of research, no one knows what there is about Jersey Hill that confounds the Ithaca pigeons, he said.
By focusing intently on their own research, scientists persuade themselves that pigeons use smell or magnetic fields or ultraviolet light to guide their way, Walcott said. They divide into warring camps, each pushing its own theory.
”The real difficulty is that we`ve all assumed we`re dealing with the same beast, so we just argue who`s right,” Walcott said. ”Maybe we`re all right.”
Walcott and others are beginning to think that a newborn pigeon has a long list of navigational abilities.
As the bird grows, it uses a few of those abilities that best suit its home territory and ignores the others. Thus, genetically identical pigeons raised only a few miles apart can display vastly different homing behavior when subjected to experiments.
Another lesson in nature`s complexity presented at the meeting concerns bats and dogbane tiger moths. The bats emit ultrasonic sounds as a sonar system to locate insects. Dogbane moths and some other species make similar ultrasonic noises.
This discovery divided scientists over whether the moths made sounds to confuse the bats or to advertise themselves to the bats because the moths are poisonous to predators and don`t want to be eaten by mistake.
William Conner, a Wake Forest University biologist, said that the moth sounds may serve a role in bat interactions, but he`s discovered that its main function apparently is in moth mating.
Scientists had shown that moths use chemical odors called pheromones to attract each other for mating. Conner`s experiments demonstrate that both pheromones and ultrasonic sounds are used in mating and that other cues are probably also at work.
”In an area thick with pheromone odors, it`s likely that sound plays a dominant role,” Conner said. ”In a noisy area, the odors probably become dominant. What we`re seeing is that nature is very versatile.”
Experiments that focused only upon pheromones or upon ultrasound would fail to uncover any connection to mating, so scientists would continue to argue only about what the moth sounds meant to bats.
And finally, there is the case of the pulsar that wasn`t there, or at least hasn`t really been seen.
Astronomers have been excited since last year by discovery of a pulsar, an extremely dense mass of neutrons, among the remnants of an exploded star called Supernova 1987A. It fits existing theory and stimulated astronomers to prepare many new papers for publication.
But a paper set for the association`s meeting was withdrawn, said John Middleditch of the Los Alamos National Laboratory, because he and colleagues had found their discovery was caused by a faulty camera, not an actual pulsar. Astronomers around the world were ”pretty disgusted” with the news, Middleditch confided, adding, ”I was pretty disgusted myself.”
In their eagerness to discover a pulsar in a supernova, the astronomy team and colleagues around the world accepted a faulty sighting and neglected to double-check their equipment and avoid international embarrassment.
To an outsider, that might not seem very scientific, but in truth it isn`t that rare.
The truly unusual thing about last year`s cold fusion excitement isn`t that the initial claims fizzled under scrutiny, but that they received so much publicity before melting away.
The point isn`t that scientists are incompetent, stupid or sloppy, but that they are human. And nature is not only complex, but also totally uncaring about the elegance of theories or experiments humans concoct to understand it. Good citizens, like good scientists, must remain skeptical of simple or easy answers, no matter how appealing.
