Today, nature takes revenge. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Edward Tenner's new book, Why Things Bite Back, is subtitled Technology and the Revenge of Unintended Consequences. And that, in a nutshell, is Tenner's message. When we apply our technologies to the world around us, things do indeed bite back.

In other episodes (e.g., 81, 457) I talk about the way a new safety device lulls us into carelessness and increases accidents -- how pesticides and germicides breed new and tougher insects and diseases. Tenner's idea isn't new, but he does a fine job of rearticulating and re-emphasizing it. Tenner's Revenge Effect means that, if we mess with the natural order of things, things bite back.

He takes care not to be simplistic in his examples. New technologies certainly do improve the quality of our lives. Medical procedures have reduced the time we spend in hospitals and hastened recoveries. Yet the number of procedures and medications a patient undergoes has risen astronomically. Laparoscopic gall bladder removals, for example, are much less invasive than old-fashioned surgery. The result is, far more people are having their gall bladders removed and insurance costs are rising. Worse still, we now find surgeons making more mistakes when they use a grainy fiber-optic image on a TV screen to guide miniaturized instruments.

Medicine has been shot through with routine hi-tech medications, catheterizations, injections, IVs ... Errors in a tiny percentage of these procedures cause widespread harm because so many are done.

We suffer so many revenge effects in medicine because the human system is terribly complex and still poorly understood. Two hospital procedures combine to produce effects that wouldn't be produced by either one alone. Three or more procedures can lay impossible demands on any doctor's knowledge of side effects.

The same thing carries over into engineering systems as they become more complex. Complex devices that interact with our human system always produce revenge effects. Tenner talks about computers -- the way they've made our work routines less straightforward than handling paper. We lose enormous time and money learning software that never stands the test of time. Meanwhile, eye strain, neck strain, and carpal tunnel syndrome all increase.

So does this mean we should reject new medicine and turn away from computers? Hardly! New technology is bred in our bones. The day we quit pioneering, we quit being human.

The answer is as subtle as the problem itself. Nature demands a wearing-in process. We have to be alert to early warnings and ready to back off. Wanting too much is what causes us to ignore those warnings and react too slowly. And every time we fail to listen, nature will forcefully get our attention.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Tenner E., Why Things Bite Back: Technology and the Revenge of Unintended Consequences. New York: Alfred A. Knopf, 1996.