February 9, 2004
Evolutionary biology has been much in the news of late. A federal judge ordered the Cobb County school board in Georgia to remove stickers from its high school biology books that declared evolution was just theory, not fact. The Dover, Pennsylvania, school board wants to order its biology teachers to instruct their students on the theory of intelligent design. The Kansas State Board of Education is considering a proposal that would change the definition of science, drawing a distinction between an allegedly dogmatic "naturalism" and "following the evidence wherever it leads." This shift in language accommodates intelligent design theory, because the "evidence" may point to a supernatural designer.
Intelligent design theory got a hearing earlier this week in the New York Times with an op-ed from biochemist Michael Behe, author of the ur-text of the movement, Darwin's Black Box: The Biochemical Challenge to Evolution. Intelligent design is a revival of the idea propounded by the Anglican divine William Paley in 1802 in his Natural Theology. Paley famously offers the example of walking across a heath and coming upon a watch. Unlike a stone, we would note its complex mechanism and, he argues, "the inference we think is inevitable, that the watch must have had a maker." Because biological organisms too are complex and well fitted for their environments, we must inevitably conclude that biology points to the existence of a supreme watchmaker God.
In the Times, Behe's first two arguments simply repeat Paley's assertions: We see apparent design in nature, and biological organisms are complicated machines like watches. Behe's third claim is that "we have no good explanation for the foundation of life that doesn't involve intelligence." The "foundation" at which Behe is pointing are the tiny molecular machines that lie within living cells, which he claims are "irreducibly complex." In his book, Behe writes: "By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning."
He further argues that such irreducibly complex systems cannot evolve over time since the lack of any one part means that the whole cannot work and that the organism would die (or never come into existence in the first place). He cites many examples of biological systems he regards as being "irreducibly complex," including the operation of bacterial flagella and blood clotting in vertebrates. Behe flatly claims that "there are no research studies indicating that Darwinian processes can make molecular machines of the complexity we find in the cell."
First, it's curious that Behe limits the force of his argument regarding design to the irreducible complexity of cellular machinery. He clearly accepts that the fossil record shows the development of species over vast stretches of time, and that this proves that evolution of bodies of plants and animals certainly occurs. But what could make a peach, a parrot, a pterosaur, and a panda different from one another, except that the molecular machinery inside their cells operates differently? It's not as though they are made up of the same irreducibly complex cells that are simply arranged to look like peaches, parrots, pterosaurs, and pandas.
So how can Behe account for such variations unless it is the case that molecular machinery can evolve step by step in order to produce the diversity of organisms that exists in the world? Behe even agrees, "Homologies among proteins (or organisms) are the evidence for descent with modification—that is, for evolution." Behe evidently believes that proteins and cellular machinery can evolve a little bit, but not a lot.
Behe seems to be demanding that every step in complex molecular cascades must be worked out—and then justified somehow with empirical evidence—or else they are irreducibly complex. Fine as far as it goes, but he rules out empirical evidence such as gene duplications, interspecies gene homologies (such as the fact that the same master control gene for producing eyes is found in flatworms, fruit flies, frogs, and mice), and less complicated cascades operating in less complex organisms.
For example, molecular biologists have worked out a plausible testable hypothesis for how such a blood clotting sequence has evolved by natural selection. Behe replies that the proffered explanation is inadequate to explain the irreducibly complex blood clotting in vertebrates. But Behe's objections are in turn refuted. Recent studies comparing vertebrate genomes finds molecular evidence indicating that blood clotting has evolved over the past 450 million years after tetrapods (four footed critters) diverged from bony fish.
Behe would likely respond that the blood clotting system was already irreducibly complex 450 million years ago-what happened before then? His evident conclusion is that the intelligent designer intervened at that point. But if you cut an invertebrate, does it not bleed? And more to the point, does its blood not clot? Indeed it does, and precursors of the proteins involved with vertebrate clotting can be found in them. All of the steps of how blood clotting may have evolved have not been worked out to Behe's satisfaction yet, but what if one day they are?
Behe might then reply, all fine and well for blood clotting. But what about the bacterial flagella? This kind of response invites an infinite regress of demanded explanations: If the bacterial flagella are explained, what about the optic nerve, the Krebs cycle, and so forth? Behe's intelligent designer becomes uncomfortably trapped in the ever-smaller gaps of biology that remain to be explained.
Behe's fourth and final claim in his New York Times op-ed is "in the absence of any convincing non-design explanation, we are justified in thinking that real intelligent design was involved in life." When push comes to shove, Behe's objections seem confined to Darwinian natural selection. As he writes: "EVIDENCE OF COMMON DESCENT IS NOT EVIDENCE OF NATURAL SELECTION" (emphasis his). But natural selection is an awfully good explanation not only for the origin of species, but also for things like aging and disease resistance (which are also governed by the operation of tiny cellular machines).
But enough evolutionary biology. Why not let children in public schools hear arguments for intelligent design in biology classes? After all, if one goes to the Internet, one can readily see that the hardy band of intelligent designers has sparked an immense debate. Biologists would retort by asking, "So it's OK with you for high schools to teach astrology, phrenology, mesmerism, psychoanalysis, water witching, and so forth, too?" And that's a good point.
Intelligent design theorists and their claims to scientific legitimacy aside, the only reason the vast majority of people who want intelligent design taught in high school want it is because they believe it will undercut the corrosive effects of evolutionary biology on the religious beliefs of their children. They don't know and couldn't care less about the scientific details of the evolution of blood cascades—they just want Darwinism kept away from their kids. However, the fact that Pope John Paul II doesn't have any problem with evolutionary biology is a pretty good indication that religious belief and biology can co-exist.
So what to do? It is not the role of public schools to confirm the religious beliefs of their students. Parents who want their children to benefit from the latest findings of science would reasonably be irked if evolutionary biology were expunged from the public school curriculum. There is another way around this conundrum. Get rid of public schools. Give parents vouchers and let them choose the schools to which to send their children. Fundamentalists can send their kids to schools that teach that the earth was created on Sunday, October 23, 4004 BC. Science geeks can send their kids to technoschools that teach them how to splice genes to make purple mice. This proposal lowers political and social conflict, and eventually those made fitter in the struggle for life by better education will win. At least that's my theory.
Ronald Bailey is Reason's science correspondent. His new book, Liberation Biology: A Moral and Scientific Defense of the Biotech Revolution, will be published by Prometheus Books in 2005.