Why scientists dismiss 'intelligent design'

By Ker Than

updated 2:30 p.m. ET Sept. 23, 2005

In his highly influential book "The Structure of Scientific Revolutions," science philosopher Thomas Kuhn presented the idea that science is not a gradual progression toward truth, but a series of insurgencies, with scientific theories constantly usurping one another.

That is sometimes true. And proponents of intelligent design love Kuhn's argument.

They see intelligent design (often called ID) as a revolutionary new science and themselves as revolutionaries. They envision toppling Darwinian evolution – once a revolutionary idea itself – and erecting in its place a theory about life that allows for supernatural explanations, a theory that makes God, or some entity very much like him, not just possible but necessary.

But in order to attract converts and win over critics, a new scientific theory must be enticing. It must offer something that its competitors lack. That something may be simplicity, which was one of the main reasons the Sun-centered model of the solar system was adopted over the Earth-centered one centuries. Or it could be sheer explanatory power, which was what allowed evolution to become a widely accepted theory with no serious detractors among reputable scientists.

So what does ID offer? What can it explain that evolution can't?

To answer this, it is necessary to examine the two main arguments — irreducible complexity and specified complexity — that ID proponents use to support their claim that a Supreme Being is responsible for many or all aspects of life.

Irreducible complexity
Irreducible complexity asserts that certain biochemical systems in nature contain parts that are too well matched to be products of evolution.

Every part of an irreducibly complex system is necessary: take away even one, and the entire system will no longer work. Because their parts are so intricate and so interdependent, such systems could not possibly have been the result of evolution, ID supporters argue.

Irreducible complexity's main proponent is Michael Behe, a biochemist at Lehigh University in Pennsylvania. Among the systems that Behe claims are irreducibly complex are the bacterial flagellum, a microscopic whip-like structure that some bacteria use to swim, and the cascade of proteins that make up the human blood-clotting system.

Darwin himself admitted that if an example of irreducible complexity were ever found, his theory of natural selection would crumble.

"If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down," Darwin wrote.

Yet no true examples of irreducible complexity have ever been found. The concept is rejected by the majority of the scientific community.

To understand why, it is important to remember that Behe's main argument is that in an irreducibly complex system, every part is vital to the system's overall operation.

A necessary — and often unstated — flipside to this is that if an irreducibly complex system contains within it a smaller set of parts that could be used for some other function, then the system was never really irreducibly complex to begin with.

It's like saying in physics that atoms are the fundamental building blocks of matter only to discover, as physicists have, that atoms are themselves made up of even smaller and more fundamental components.

This flipside makes the concept of irreducible complexity testable, giving it a scientific virtue that other aspects of ID lack.

"The logic of their argument is you have these multipart systems, and that the parts within them are useless on their own," said Kenneth Miller, a biologist at Brown University in Rhode Island. "The instant that I or anybody else finds a subset of parts that has a function, that argument is destroyed."

Viewed this way, all of the systems that Behe claims to be irreducibly complex really aren't.

A subset of the bacterial flagellum proteins, for example, are used by other bacteria to inject toxins into other cells and several of the proteins in the human blood-clotting system are believed to be modified forms of proteins found in the digestive system.

Evolution takes pieces and parts and re-uses them.

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