Detecting Design in the Natural Sciences
By William A. Dembski
[word count: 2106]
How a designer gets from thought to thing is, at least in broad strokes, straightforward: (1) A designer conceives a purpose. (2) To accomplish that purpose, the designer forms a plan. (3) To execute the plan, the designer specifies building materials and assembly instructions. (4) Finally, the designer or some surrogate applies the assembly instructions to the building materials.
What emerges is a designed object, and the designer is successful to the degree that the object fulfills the designer's purpose. In the case of human designers, this four-part design process is uncontroversial. Baking a cake, driving a car, embezzling funds, and building a supercomputer each presuppose it. Not only do we repeatedly engage in this four-part design process, but we have witnessed other people engage in it countless times. Given a sufficiently detailed causal history, we are able to trace this process from start to finish.
But suppose a detailed causal history is lacking and we are not able to trace the design process. Suppose instead that all we have is an object, and we must decide whether it emerged from such a design process. In that case, how do we decide whether the object is in fact designed? If the object in question is sufficiently like other objects that we know were designed, then there may be no difficulty inferring design. For instance, if we find a scrap of paper with writing on it, we infer a human author even if we know nothing about the paper's causal history. We are all familiar with humans writing on scraps of paper, and there is no reason to suppose that this scrap of paper requires a different type of causal story.
Nevertheless, when it comes to living things, the biological community holds that a very different type of causal story is required. To be sure, the biological community admits that biological systems appear to be designed. For instance, Oxford biologist Richard Dawkins writes, "Biology is the study of complicated things that give the appearance of having been designed for a purpose." Likewise, Nobel laureate Francis Crick writes, "Biologists must constantly keep in mind that what they see was not designed, but rather evolved."
The term "design" is everywhere in the biological literature. Even so, its use is carefully regulated. According to the biological community, the appearance of design in biology is misleading. This is not to deny that biology is filled with marvelous contrivances. Biologists readily admit as much. Yet as far as the biological community is concerned, living things are not the result of the four-part design process described here.
But how does the biological community know that living things are only apparently and not actually designed? The exclusion of design from biology certainly contrasts with ordinary life where we require three primary modes of explanation: necessity, chance, and design. Nevertheless, in the natural sciences one of these modes of explanation is considered superfluous, namely, design. From the perspective of the natural sciences, design, as the action of an intelligent agent, is not a fundamental creative force in nature. Rather, blind natural causes, characterized by chance and necessity and ruled by unbroken laws, are thought sufficient to do all nature's creating.
Darwin's theory is a case in point. According to Darwinist Francisco Ayala, "The functional design of organisms and their features would therefore seem to argue for the existence of a designer. It was Darwin's greatest accomplishment to show that the directive organization of living beings can be explained as the result of a natural process, natural selection, without any need to resort to a Creator or other external agent. The origin and adaptation of organisms in their profusion and wondrous variations were thus brought into the realm of science."
Is it really the case, however, that the directive organization of living beings can be explained without recourse to a designer? And would employing a designer in biological explanations necessarily take us out of the realm of science? The answer to both questions is No.
What has kept design outside the natural sciences since Darwin published his Origin of Species 140 years ago is the absence of precise methods for distinguishing intelligently caused objects from unintelligently caused ones. For design to be a fruitful scientific concept, scientists have to be sure that they can reliably determine whether something is designed. Johannes Kepler thought the craters on the moon were intelligently designed by moon dwellers. We now know that the craters were formed by blind natural forces.
It is this fear of falsely attributing something to design only to have it overturned later that has prevented design from entering the natural sciences. With precise methods for discriminating intelligently from unintelligently caused objects, it is now possible to formulate a theory of intelligent design that successfully avoids Kepler's mistake and reliably locates design in biological systems.
The theory of intelligent design is a theory of biological origins and development. Its fundamental claim is that intelligent causes are indispensable for explaining the complex, information-rich structures of biology, and that these causes are empirically detectable. To say intelligent causes are empirically detectable is to say there exist well-defined methods that, on the basis of observational features of the world, are capable of reliably distinguishing intelligent causes from undirected natural causes.
Many special sciences have already developed such methods for drawing this distinction -- notably forensic science, cryptography, archeology, random number generation, and the Search for Extraterrestrial Intelligence. Whenever these methods detect intelligent causation, the underlying entity they uncover is a type of information known alternately as specified complexity or complex specified information.
For instance, how did the radio astronomers in the movie Contact (a movie starring Jodie Foster and based on a novel by Carl Sagan) infer the presence of extraterrestrial intelligence in the radio signals they monitored from space? The researchers ran signals through computers that were programmed to recognize many preset patterns. These patterns act as a sieve. Signals that do not match any of the patterns pass through the sieve and are classified as random.
After years of receiving apparently meaningless random signals, the Contact researchers discover a pattern of beats and pauses that corresponds to the sequence of all the prime numbers between 2 and 101. (Prime numbers are numbers divisible only by themselves and by one.) When a sequence begins with two beats, then a pause, three beats, then a pause ... and continues all the way to 101 beats, researchers must infer the presence of an extraterrestrial intelligence.
Why? There is nothing in the laws of physics that requires radio signals to take one form or another. The sequence is therefore contingent rather than necessary. Also, it is a long sequence and therefore complex. Note that if the sequence lacked complexity, it could easily have happened by chance. Finally, it was not just complex but also exhibited an independently given pattern or specification (it was not just any old sequence of numbers but a mathematically significant one -- the prime numbers).
To summarize, an event exhibits specified complexity if it is contingent and therefore not necessary; if it is complex and therefore not easily repeatable by chance; and if it is specified in the sense of exhibiting an independently given pattern. Note that complexity in the sense of improbability is not sufficient to eliminate chance -- flip a coin long enough and you will witness a highly complex or improbable event. Even so, you will have no reason not to attribute it to chance.
The important thing about specifications is that they be objectively given and not just imposed on events after the fact. For instance, if an archer fires arrows into a wall and then paints bull's-eyes around the arrows, the archer impose a pattern after the fact. On the other hand, if the targets are set up in advance (specified), and then the archer hits them accurately, we know it was by design.
The combination of complexity and specification convincingly pointed the radio astronomers in the movie Contact to an extraterrestrial intelligence. Specified complexity is the characteristic trademark or signature of intelligence. Specified complexity is a reliable empirical marker of intelligence in the same way that fingerprints are a reliable empirical marker of a person's presence (for the theoretical justification see my book No Free Lunch, 2002).
Only intelligent causation gives rise to specified complexity. It follows that specified complexity lies beyond the capacity of blind natural causes to generate it. This is not to say that naturally occurring systems cannot exhibit specified complexity or that natural processes cannot serve as a conduit for specified complexity. Naturally occurring systems can exhibit specified complexity and nature operating without intelligent direction can take preexisting specified complexity and shuffle it around. But that is not the point. The point is whether nature (conceived as a closed system of blind, unbroken natural causes) can generate specified complexity in the sense of originating it when previously there was none.
To see what is at stake, consider a Dürer woodcut. It arose by mechanically impressing an inked woodblock on paper. The Dürer woodcut exhibits specified complexity. But the mechanical application of ink to paper via a woodblock does not account for that specified complexity in the woodcut. The specified complexity in the woodcut must be referred back to the specified complexity in the woodblock which in turn must be referred back to the designing activity of Dürer himself (in this case deliberately chiseling the woodblock). Specified complexity's causal chains end not with nature but with a designing intelligence.
When properly formulated, the theory of intelligent design is a theory of information. Within such a theory, complex specified information (or specified complexity) becomes a reliable indicator of intelligent causation as well as a proper object for scientific investigation. The theory of intelligent design thereby becomes a theory for detecting and measuring information, explaining its origin, and tracing its flow. The theory of intelligent design therefore does not study intelligent causes per se but the informational pathways induced by intelligent causes. As a result, the theory of intelligent design presupposes neither a creator nor miracles. The theory of intelligent design is theologically minimalist. It detects intelligence without speculating about the nature of the intelligence.
Biochemist Michael Behe (Darwin's Black Box, 1996) connects specified complexity to biological design. Behe defines a system as irreducibly complex if it consists of several interrelated parts so that removing even one part completely destroys the system's function. For Behe, irreducible complexity is a sure indicator of design. One irreducibly complex biochemical system that Behe considers is the bacterial flagellum. The flagellum is an acid-powered rotary motor with a whip-like tail that spins at 20,000 rpm and whose rotating motion enables a bacterium to navigate through its watery environment.
Behe shows that the intricate machinery in this molecular motor -- including a rotor, a stator, O-rings, bushings, and a drive shaft -- requires the coordinated interaction of at least thirty complex proteins and that the absence of any one of these proteins would result in the complete loss of motor function. Behe argues that the Darwinian mechanism is in principle incapable of generating such irreducibly complex systems. It can be shown that Behe's notion of irreducible complexity is a special case of specified complexity and that systems like the bacterial flagellum exhibit specified complexity and are therefore designed.
In applying the test of specified complexity to biological organisms, design theorists focus on identifiable systems -- such as individual enzymes, molecular machines, and the like -- that exhibit a clear function and for which complexity can be reasonably assessed. Of course, once specified complexity is exhibited by some part of an organism, then any design attributable to that part carries over to the whole organism. It is not necessary to demonstrate that every aspect of the whole organism is the result of design. Some aspects will be the result of chance or necessity.
Design has had a turbulent intellectual history. The chief difficulty with design to date has consisted in discovering a conceptually powerful formulation of it that will fruitfully advance science. It is the empirical detectability of intelligent causes that promises to make the theory of intelligent design a full-fledged scientific theory and distinguishes it from the design arguments of philosophers and theologians, or what has traditionally been called "natural theology."
The world contains events, objects, and structures that exhaust the explanatory resources of undirected natural causes and that can be adequately explained only by recourse to intelligent causes. The theory of intelligent design demonstrates this rigorously. It thus takes a long-standing philosophical intuition and transforms it into a scientific research program.