The Flaw in the Mousetrap: Intelligent design fails the biochemistry test.

To understand why the scientific community has been unimpressed by attempts to resurrect the so-called argument from design, one need look no further than Michael J. Behe’s own essay. He argues that complex biochemical systems could not possibly have been produced by evolution because they possess a quality he calls irreducible complexity. Just like mousetraps, these systems cannot function unless each of their parts is in place. Since “natural selection can only choose among systems that are already working,” there is no way that Darwinian mechanisms could have fashioned the complex systems found in living cells. And if such systems could not have evolved, they must have been designed. That is the totality of the biochemical “evidence” for intelligent design.

Parts of a supposedly irreducibly complex machine may have different, but still useful, functions.

Ironically, Behe’s own example, the mousetrap, shows what’s wrong with this idea. Take away two parts (the catch and the metal bar), and you may not have a mousetrap but you do have a three-part machine that makes a fully functional tie clip or paper clip. Take away the spring, and you have a two-part key chain. The catch of some mousetraps could be used as a fishhook, and the wooden base as a paperweight; useful applications of other parts include everything from toothpicks to nutcrackers and clipboard holders. The point, which science has long understood, is that bits and pieces of supposedly irreducibly complex machines may have different — but still useful — functions.

Evolution produces complex biochemical machines.

Behe’s contention that each and every piece of a machine, mechanical or biochemical, must be assembled in its final form before anything useful can emerge is just plain wrong. Evolution produces complex biochemical machines by copying, modifying, and combining proteins previously used for other functions. Looking for examples? The systems in Behe’s essay will do just fine.

Natural selection favors an organism’s parts for different functions.

He writes that in the absence of “almost any” of its parts, the bacterial flagellum “does not work.” But guess what? A small group of proteins from the flagellum does work without the rest of the machine — it’s used by many bacteria as a device for injecting poisons into other cells. Although the function performed by this small part when working alone is different, it nonetheless can be favored by natural selection.

The blood clotting system is an example of evolution.

The key proteins that clot blood fit this pattern, too. They’re actually modified versions of proteins used in the digestive system. The elegant work of Russell Doolittle has shown how evolution duplicated, retargeted, and modified these proteins to produce the vertebrate blood-clotting system.

Working researchers see evolution in subcellular systems.

And Behe may throw up his hands and say that he cannot imagine how the components that move proteins between subcellular compartments could have evolved, but scientists actually working on such systems completely disagree. In a 1998 article in the journal Cell, a group led by James Rothman, of the Sloan-Kettering Institute, described the remarkable simplicity and uniformity of these mechanisms. They also noted that these mechanisms “suggest in a natural way how the many and diverse compartments in eukaryotic cells could have evolved in the first place.” Working researchers, it seems, see something very different from what Behe sees in these systems — they see evolution.

Behe’s points are philosophical, not scientific.

If Behe wishes to suggest that the intricacies of nature, life, and the universe reveal a world of meaning and purpose consistent with a divine intelligence, his point is philosophical, not scientific. It is a philosophical point of view, incidentally, that I share. However, to support that view, one should not find it necessary to pretend that we know less than we really do about the evolution of living systems. In the final analysis, the biochemical hypothesis of intelligent design fails not because the scientific community is closed to it but rather for the most basic of reasons — because it is overwhelmingly contradicted by the scientific evidence.