First Things 64 (June/July 1996): 13-14

DNA: The Message in the Molecule


By Nancy R. Pearcey

Christians who work in the natural sciences are dogged by a persistent bogeyman: a singular creature called the God of the gaps. Should a believer ever conclude that natural forces are inadequate to produce some phenomenon in the natural world, the bogeymen is poised to spring from the shadows. Its power to intimidate can be seen in an essay by philosopher Nancey Murphy in Perspectives on Science and Christian Faith in which she backs away from any suggestion that Christians ought to challenge naturalism in science. Murphy argues that believers are properly "wary of invoking divine action in any way in science, especially in biology, fearing that science will advance, providing the naturalistic explanations that will make God appear once again to have been an unnecessary hypothesis." Such Christians fear being cast in the same category as primitives attributing thunder to the raging of their gods.

But in a deft turning of the tables, Stephen M. Barr conjured up a counter-spook in "The Atheism of the Gaps" (First Things, November 1995). We are so conditioned to expect scientific breakthroughs that exceed our expectations, Barr observed, that we reflexively reject any idea that science has limits. Yet science reveals not only the rich possibilities of nature but also its limitations. To give obvious examples, we know that we will never fulfill the alchemists' dream of chemically transmuting lead into gold. We know that a parent of one species will never give birth to offspring of another species. Science reveals consistent patterns that allow us to make negative statements about what natural forces cannot do. To persist in seeking natural laws in such cases, Barr suggested, is as irrational as any primitive myth of the thunder gods.

The example Barr considered was human consciousness, focusing on Roger Penrose's argument that the mind cannot be explained by currently known laws of physics. As a convinced materialist, Penrose holds out the hope that new and unimaginable physical laws are nonetheless out there, just waiting to be discovered. As Barr comments, materialism clearly functions for Penrose as a faith of the gaps: When science reveals phenomena that surpass the explanatory power of known natural laws, materialism takes refuge in the hope of turning up "undiscovered and unprecedented" laws, different in kind from any currently known.

Another field that often elicits the materialist's faith of the gaps is origin-of-life research. The discovery of DNA revealed that at the core of life is a molecular message that contains a staggering quantity of information. A single cell of the human body contains as much information as the Encyclopedia Britannica-all thirty volumes of it-three or four times over. As a result, the question of the origin of life must now be recast as the origin of biological information. The materialist is committed to constructing an explanation that appeals solely to physical-chemical laws. And it is true that the bases, sugars, and phosphates comprising the nucleotides in DNA are ordinary chemicals that react according to ordinary laws. Yet those same laws do not explain how the chemicals came to function as a cellular language.

We know, after all, the characteristic effects of physical forces: They create either random patterns, like the pile of leaves against my back fence, or else ordered, repetitive structures, like ripples on a beach or the molecular structure of crystals. But information theory teaches us that neither random nor repetitive structures carry high levels of information.

The information content of any structure is defined as the minimum number of instructions needed to specify it. For example, a random pattern of letters has a low information content because it requires very few instructions: 1) Select a letter of the English alphabet and write it down, and 2) Do it again. A highly ordered but repetitive pattern likewise has low information content. Wrapping paper with "Merry Christmas" printed all over in ornate gold letters is highly ordered, but it can be specified with very few instructions: 1) Write "M-e-r-r-y C-h-r-i-s-t-m-a-s," and 2) Do it again.

By contrast, a structure with high information content requires a large number of instructions. If you want your computer to print out the poem "'Twas the Night Before Christmas," you must specify every letter, one by one. There are no shortcuts. This is the kind of order we find in DNA. It would be impossible to produce a simple set of instructions telling a chemist how to synthesize the DNA of even the simplest bacterium. You would have to specify every chemical "letter," one by one.

The high level of complexity in DNA has led researchers to abandon chance theories of life's origin in favor of theories of spontaneous self-organization. The guiding principle in the field today is (in the words of chemist Cyril Ponnamperuma) that "there are inherent properties in the atoms and molecules which seem to direct the synthesis in the direction most favorable" for producing the macromolecules of life. But so far no one has been able to identify these mysterious self-organizing properties. The best that scientists can do is draw analogies to spontaneous ordering in nonliving structures, such as crystals.

The unique structure of any crystal is the result of what we might think of as the "shape" of its atoms (or ions), which causes them to slot into a particular position and to layer themselves in a fixed, orderly pattern. "If we could shrink ourselves to the atomic scale," writes zoologist Richard Dawkins in The Blind Watchmaker, "we would see almost endless rows of atoms stretching to the horizon in straight lines-galleries of geometric repetition."

Many scientists find it irresistible to draw an analogy between this example of spontaneous ordering and the origin of DNA. For example, chemist Graham Cairns-Smith proposes that DNA originated by sticking to the surface of crystals in certain clays, with the crystals acting as a template to organize life's building blocks in precise arrays. In Darwin's Dangerous Idea, philosopher Daniel Dennett goes so far as to speak of DNA as itself a carbon-based, self-replicating crystal.

But the fatal flaw in all such theories is that crystals, while highly ordered, are low in information content. The structure of a crystal is strictly repetitive-"galleries of geometric repetition." If the forces that produced DNA were analogous to those that produce a crystal, then DNA would consist of a single or at most a few patterns repeating again and again-like Christmas wrapping paper-and it would be incapable of storing and transmitting large quantities of information.

Nor is this problem solved by newer theories of complexity. In At Home in the Universe, Stuart Kauffman claims that complexity theory will uncover laws that make life inevitable. But the ferns, swirls, and snowflakes that complexity theorists construct on their computer screens represent the same kind of order as crystals. In Kauffman's words, they are constructed by the repeated application of a few "astonishingly simple rules." Like crystals, these structures can be specified with only a few instructions, followed by "Do it again."

The upshot is that DNA exhibits too much "design work" (as Cairns-Smith puts it) to be the product of mere chance, yet there are no known physical laws capable of doing the necessary work. Once we apply the tools of information theory, all the plausible candidates fall out of the race. No known physical laws produce the right kind of ordered structure: one with high information content.

This is not a statement about our ignorance-a "gap" in knowledge that one might be tempted to bridge with an appeal to the supernatural. Rather, it is a statement about what we know-about the consistent character of natural laws. If the structure of the DNA molecule were a regular, repeated pattern, then it would make sense to look for a general law of assembly to explain its origin. But instead we must look for something that specified each nucleotide one by one.

We also know, from information theory, how codes work. Encoded messages are independent of the physical medium used to store and transmit them. If we knew how to translate the message in a DNA molecule, we could write it out using ink or crayon or electronic impulses from a keyboard. We could even take a stick and write it in the sand-all without affecting its meaning. In other words, the sequence of "letters" in DNA is chemically arbitrary: There is nothing intrinsic in the chemicals themselves that explains why particular sequences carry a particular message. In the words of chemist-turned-philosopher Michael Polanyi, the sequence of nucleotides is "extraneous to" the physical and chemical properties within the molecule-which is to say, the sequence is not determined by inherent physical-chemical forces. In fact, it is precisely this "physical indeterminacy" (Polanyi's phrase) that gives nucleotides the flexibility to function as letters in a message-to be arranged and rearranged in a host of unpredictable patterns, like the letters on a page. But physical indeterminacy also implies that physical forces did not originate the pattern-any more than the text on this page originated from the physical properties of the paper and ink.

If we consult everyday experience, we readily note that objects with a high information content-books, computer disks, musical scores-are products of intelligence. It is reasonable to conclude, by analogy, that the DNA molecule is likewise the product of an intelligent agent. This is a contemporary version of the design argument, and it does not rest on ignorance-on gaps in knowledge-but on the explosive growth in knowledge thanks to the revolution in molecular biology and the development of information theory.

In spite of this extensive new evidence, the materialist continues to hold out for the discovery of some new physical laws to explain the origin of biological information. As chemist Manfred Eigen writes in Steps Towards Life, "Our task is to find an algorithm, a natural law that leads to the origin of information." Yet no known natural forces produce structures with high information content, and so the elusive law that Eigen hopes to find must be different in kind from any we currently know. Surely that qualifies as an argument from ignorance-the materialist's God of the gaps.

Nancy R. Pearcey is Fellow and Policy Director of the Wilberforce Forum, and coauthor with Charles Thaxton of The Soul of Science (Crossway).