Was it REALLY news to anybody, as headlines proclaimed a little more than a week ago, that smoking causes lung cancer?
The discovery behind the news stories was a report by a team of scientists showing that benzo(a)pyrene, a chemical in cigarette smoke, causes genetic mutations in lung cells that are identical to those found in many patients with lung cancer.
That this unsurprising discovery made such a big splash illustrates a curiously unintuitive idea: When it comes to proof, sometimes scientists are easier to please than ordinary people.
Benzo(a)pyrene has been recognized as a carcinogen for 20 years, but its exact mechanism was unknown. And the tobacco industry exploited that seed of doubt to the fullest, arguing that although scientists had shown an association between smoking and cancer, they had not proved cause and effect.
The new study was seen as the proof that would silence the tobacco industry. It was the first proof, on the cellular and molecular level, that a chemical in smoke could damage lung cells in a way that could eventually lead to cancer. But who was actually swayed by the study?
"From the point of view of scientists and doctors, and many people who are reasonably educated in medicine, this finding will make virtually no difference at all," said John Banzhaf, a professor of law at Georgetown University and the director of Action on Smoking and Health, an anti-smoking group.
"There are so many different studies of so many different kinds which establish about as conclusively as anything we know in medicine that smoking causes cancer in human beings, that this doesn't really help," Banzhaf said. "We already have 50,000 studies. Why do we need 50,001?"
This last bit of proof is for ordinary people. Scientists and lay people have different ideas about what constitutes proof, Banzhaf said. Part of scientific training involves learning to deal with uncertainty.
If a statistical analysis shows that there is a 5 percent or smaller chance that two events -- say, smoking and cancer -- are linked purely by coincidence, then most scientists would accept the idea that the association between them has at least a 95 percent chance of being real and likely to repeat itself, even if the nature of the link is not fully understood.
But non-scientists, less familiar with statistics, may not be able to let go of that 5 percent, or the lack of an explanation. They may insist that proof does not exist until all competing possibilities have been eliminated.
Their notions of "reasonable doubt" in criminal cases, or of the "preponderance of evidence" that is required in civil court, may be colored by their discomfort with uncertainty.
Pinning down a mechanism -- being able to say, this molecule causes this change in this cell, which is known to lead to cancer -- eliminates some of the uncertainty. People are more likely to believe in things that they can understand.
But some may never be persuaded. The Tobacco Institute said it wasn't ready to comment. RJR Nabisco, the cigarette manufacturer, called the study "preliminary rather than conclusive." Philip Morris said it is "extremely interesting and merits careful review."
One of the nagging issues, and a favorite of the defenders of smoking, is the question of why not all smokers get lung cancer. Knowing the mechanism may help provide an answer. Scientists may one day be able to say that people may differ in the tendency of their cells to convert benzo(a)pyrene to a highly carcinogenic form, or in the ability of their cells to repair the sort of genetic damage that the chemical inflicts, said one of the authors of the study, Dr. Gerd Pfeifer, an associate professor at the Beckman Research Institute at the City of Hope in Duarte, Calif.
The availability of an explanation has made the connection between smoking and cancer less of an abstraction for some people. Idee Fox, a Philadelphia judge who quit smoking a month ago and who still craves cigarettes, said, "This report really meant something to me as a smoker. I had been thinking, not everybody who smokes gets cancer, they don't really understand it, so maybe it won't happen to me. This explained how it works, and made it more real."
People who want to rationalize smoking may now have to turn to philosophy for solace.
"Theoretically, you can never prove anything," said Dr. Bert Vogelstein, a Johns Hopkins expert in cancer genetics. "No one will ever be able to prove that smoking causes cancer, or that anything causes anything."