Creationism, evolution: What's in a theory?

It’s a perennial. Every year school boards debate whether to teach creationism alongside the theory of evolution. They are both explanations for the origin of life, the argument goes, and we should be open-minded because students have a right to hear every point of view.

The debate has been going on since Darwin published “The Origin of Species� in 1859, when, all of a sudden, the world was older, less stable, and it was not necessary to invoke the hand of God to explain how the world came to be as it is.

A visitor from that time to our own would recognize the conflicts we have been having. In 2005, a federal judge ruled that intelligent design is a form of creationism and should not be taught in science classes (Kitzmiller v. Dover Area School District). That stopped most lawsuits, but the issue does not die and probably never will. It has retreated from the courts to state legislatures and textbook publishing companies.

One source of confusion is the word “theory,� which, to most people, does not connote proven, although some theories are beyond doubt. To scientists, there is another aspect of the word, as I was reminded recently in an old book by Emile Duclaux. Professor Duclaux was one of the first students of Louis Pasteur and later became head of the Pasteur Institute. He wrote that a theory does not need to be philosophical and seducing; it does not even need to be true in the absolute sense of the word; it suffices that it be fertile.

Fertile? He was referring to the germ theory of disease, not the theory of evolution. In 1862, when Duclaux was a student with Pasteur, most people thought bacteria formed spontaneously. Inanimate chemicals just got together to form a living thing that could then grow and divide and make more of itself.

It is hard to believe now, but in 1862 that was what every medical student learned. It was an old idea — Aristotle believed that eels formed from the silt of rivers.

Pasteur emphatically said there was no such thing as spontaneous generation. Bacteria come from pre-existing bacteria and they are ubiquitous. If you believe in spontaneous generation of bacteria, he said, you have no incentive to keep bacteria out of wounds, no need to wash your hands before delivering a baby, no need to clean your surgical instruments. Why bother if bacteria appear spontaneously and do not come from dirty hands or filthy bandages?

Pasteur insisted that if you understand the germ theory of disease and you sterilize hands and instruments, fewer patients die of infection. We still call this the germ theory of disease even though it is universally accepted. It made people ask questions — is cholera caused by bacteria? What about anthrax or diphtheria? All yes. None of the many believers in spontaneous generation ever wondered. Their theory was not fertile.

What of the theory of evolution, which predicts the selection of useful variants over billions of years to explain the diversity of life in a changing world, and biblical creationism, which supposes a stable world created relatively recently? Which theory is most fertile?

Which would be most useful in thinking about an outbreak of drug-resistant bacteria? Or in understanding the appearance of new flu or HIV viruses? How is it that a gene that affects the eye of a fruit fly also affects the human eye?

The theory of evolution runs like background music in the mind of every working biologist because, as a famous scientist once said, “Nothing in biology makes sense except in the light of evolution.� A creationist approach to biology may be comforting — it connotes a stable, non-materialistic world — but for scientific progress, it induces no questions and it isn’t fertile. It is a distinction that students should learn.

So at the risk of hate mail from the ACLU (they wouldn’t, would they?), let me propose a change of tack for biology teachers and school boards. Teach intelligent design next to evolution, but mind Prof. Duclaux’s word: fertile. Ask which theory prompts questions, ideas and experiments.

I admit this could be tricky. One thing to avoid is an antagonistic approach. There is no virtue in bullying a teenager. It might help to remind students that there are believing scientists, in all traditions, who accept evolution and use it every day. Francis Collins, the director of our National Institutes of Health, has written on the subject and his book may convince religious students to try science. God knows we need them.

Richard Kessin is professor of pathology and cell biology at Columbia University. He and his wife, Galene, live in Norfolk.