In the mid-1970s I learned a lesson about identifying culprits while I was cutting my scientific teeth, conducting experiments on the territorial behavior of hummingbirds. The study was conducted in one of the dry riparian canyons that were ubiquitous along the coastal counties of southern California before they were transformed into a patchwork of housing developments.

Although there were fewer people in the greater Los Angeles area then, there was no shortage of troublemakers. These were the stomping grounds of the infamous Manson "family." After having a pair of binoculars stolen from my well-worn 1967 Volkswagen beetle, I began keeping a wary eye out for the bad guys. Weeks later, after tuning up the bug, I gave it a quick test drive down the canyon. When a car passed by going the other way, I thought it best to turn around and return just in case. I arrived at my makeshift outdoor work site just in time to stop someone walking away with my tool box: "Sorry, man! I thought that somebody just, like, left it here, man." "Right," I thought, as I vowed to increase my vigilance against thieves.

But my real lesson in vigilance came from a trickier case. The experiments on territorial behavior that I was conducting involved the provisioning of artificial flowers by infusion pumps. The pumps delivered a sucrose solution through a long tube that stretched from a syringe to the artificial flowers from which the hummingbirds would feed. As each pump slowly squeezed the syringe throughout the day, a flower was supplied with the solution. The mechanics sound simple, but Murphy's Law applies with great force to any experiment run outside the walls of a laboratory. After several exasperating problems imposed by weather, friction, evaporation, and the hummingbirds themselves, all was finally working well. Then, midway through an

experiment, the vandals struck. When my assistants and I arrived to gather data one morning, the tubing to each flower had been sliced to pieces. Hoping that the act was just an isolated event, we replaced all of the tubing, wrote a threatening sign to ward off the troublemakers, and resumed the equilibration period to allow data collection on the following day. When we arrived in the morning, we found the tubing cut to pieces again. Exasperated and angry, we again repaired the damage, and I wrote a more severe warning about the consequences of interfering with government-supported research, adding that violators would be prosecuted.

Under the heavy influence of adrenaline and testosterone, I returned to the site before dark, thinking that I would wait there and scare off the creeps, hoping that they were little creeps and thinking about what kind of weapons I might be able to improvise if they turned out to be big creeps—the rocks in the streambed perhaps. I was too late. The vandals had already been there, but I must have interrupted them because only a few tubes had been cut. I sat down with tubing in hand next to my impotent warning signs, trying to think what my next escalation should be, keeping an eye and an ear out for anyone who had not yet escaped. Looking at the tubing, I noticed that, strangely, each cut had been made at the same slight angle from perpendicular. Parallel to each cut was a thin scoring of the tubing; it was just one sixteenth of an inch to the side of the cut edge and spanned only half the circumference of the tubing. Having cut the tubing with scissors many times, I realized that scissors did not make that kind of parallel mark. Nor would a knife. Then I guessed, correctly as it turned out, what implement would. I looked around slowly and carefully, and there, near some willows on the opposite side of the stream bank, staring right back at me, was the vandal: a brown towhee. Between its eyes was the destructive implement. Adapted to breaking seeds, that bill could make short work of the strange, long, squishy food with the drippy, sweet reward. The edge of the lower bill severed the tubing as it pressed up against the inside of the upper bill, while the edge of the upper bill left the telltale scoring just next to the cut. I looked back at my warning sign, feeling foolish about threatening a bird with prosecution.

My resolution of the problem had been delayed because I jumped to the wrong conclusion about its cause. Had I thought more broadly about the spectrum of possible causes, I could have resolved the matter much more quickly. On the bright side, it did not take me decades to figure out that my original line of thinking was leading me down the wrong path; and thousands of people did not die as a result of my misguided reasoning.

Unfortunately, the same cannot be said for medicine. Thousands suffered and died because antibiotic treatment of peptic ulcers was generally recognized in 1995 instead of 1955. Thousands more probably suffered and died over a similar period because cervical cancer was treated as bad luck rather than a preventable sexually transmitted disease. It would be gratifying if we could be confident that these oversights were a thing of the past, that lessons had been learned and the health sciences now objectively consider and present the spectrum of feasible explanations for the cause and control of diseases. But the record does not support this optimistic view, not when we assess the last two centuries of medical progress, nor when we assess the last two decades. We have no reason to think that suddenly in the year 2000 the mind-set and the biases have changed.

Cancers, heart attacks, stroke, Alzheimer's disease, and infertility are like the acts of an anonymous vandal. Together they are the primary reason our life expectancy is what it is. Experts say that causation is multifactorial; they consider risk factors but shy away from considering primary causes. Infectious agents are sometimes mentioned, but they are often dismissed without justification. If the true culprit is not suspected, we have little recourse for controlling it. The possible culprits fall into three general categories. One is bad genes. Another comprises harmful noninfectious aspects of the environment such as radiation, noxious chemicals, and dietary imbalances. The third is infectious damage caused by viruses, bacteria, and other parasites—culprits that medicine thought it understood and had under control a quarter century ago. This last category has been grievously underestimated.

Modern medicine is not nearly as far advanced as the textbooks and most physicians would have us believe. It is now more important than ever to identify the weaknesses and mistakes of our medical establishment, not for the purpose of attacking hardworking doctors, but rather to suggest ways to better understand the predicament we are in at the beginning of the twenty-first century and the range of options that we have at our disposal for overcoming the very present danger we ' face.