Intelligent Design: A Brief Introduction

By William A. Dembski

Intelligent design (ID) studies patterns in nature that are best explained as the result of intelligence. Is that radio signal from outer space just random noise or the result of an alien intelligence? Is that chunk of rock just a random chunk of rock or an arrowhead? Is Mount Rushmore the result of wind and erosion or the creative act of an artist? We ask such questions all the time, and we think we can give good answers to them.

Yet, when it comes to biology and cosmology, scientists balk at even raising such questions, much less answering them in favor of design. This is especially true of biology. According to well-known evolutionist Francisco Ayala, Darwin's greatest achievement was to show how the organized complexity of organisms could be attained without a designing intelligence. By contrast, ID purports to find patterns in biological systems that signify intelligence. ID therefore directly challenges Darwinism and other materialistic approaches to the origin and evolution of life.

The idea of design has had a turbulent intellectual history. The main challenge facing it these last 200 years has been to discover a conceptually powerful formulation of it that will fruitfully advance science. What has kept design outside the scientific mainstream since Darwin proposed his theory of evolution is that it lacked precise methods for distinguishing intelligently caused objects from unintelligently caused ones. For design to be a fruitful scientific concept, scientists need to be sure they can reliably determine whether something is designed.

Johannes Kepler, for instance, thought the craters on the moon were intelligently designed by moon dwellers. We now know that the craters were formed by blind material forces (like meteor impacts). It's this fear of falsely attributing something to design only to have it overturned later that has prevented design from entering science proper. But design theorists argue that they now have formulated precise methods for discriminating designed from undesigned objects. These methods, they contend, enable them to avoid Kepler's mistake and reliably locate design in biological systems.

As a theory of biological origins and development, ID's central claim is that only intelligent causes can adequately explain 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, based on observable features of the world, can reliably distinguish intelligent causes from undirected material causes. Many special sciences have already developed such methods for drawing this distinction-notably forensic science, cryptography, archeology, and the Search for Extraterrestrial Intelligence (SETI). Essential to all these methods is the ability to eliminate chance and necessity.

Astronomer Carl Sagan wrote a novel about SETI called Contact, which was later made into a movie starring Jodie Foster. After years of receiving apparently meaningless "random" radio signals from outer space, the Contact researchers discovered a pattern of beats and pauses that corresponded to the sequence of all the prime numbers from 2 to 101. (Prime numbers are divisible only by themselves and by one.) That got their attention, and they immediately inferred a designing intelligence. When a sequence begins with two beats, then a pause, three beats, then a pause ... and continues through each prime number all the way to 101 beats, researchers must infer the presence of an extraterrestrial intelligence.

Why is that? Nothing in the laws of physics requires radio signals to take one form or another, so the prime sequence is contingent rather than necessary. Also, the prime sequence 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).

Intelligence leaves behind a characteristic trademark or signature-what I call "specified complexity." (See my book No Free Lunch.) An event exhibits specified complexity if it is contingent and therefore not necessary; if it is complex and therefore not readily reproducible by chance; and if it is specified in the sense of exhibiting an independently given pattern. Note that a merely improbable event is not sufficient to eliminate chance-flip a coin long enough and you'll witness a highly complex or improbable event. Even so, you'll 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 we paint bull's-eyes around them, we 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.

In determining whether biological organisms exhibit specified complexity, design theorists focus on identifiable systems-such as individual enzymes, metabolic pathways, molecular machines, and the like. These systems are specified by their independent functional requirements and they exhibit a high degree of complexity. Of course, once an essential part of an organism exhibits specified complexity, then any design attributable to that part carries over to the organism as a whole. One need not demonstrate that every aspect of the organism was designed; in fact, some aspects will be the result of purely material causes.

The combination of complexity and specification convincingly pointed the radio astronomers in the movie Contact to an extraterrestrial intelligence. Within the theory of intelligent design, specified complexity is the characteristic trademark or signature of intelligence. It is a reliable empirical marker of intelligence in the same way that fingerprints are a reliable empirical marker of an individual's presence at the scene of a crime. Design theorists contend that undirected material causes, like natural selection acting on random genetic change, cannot generate specified complexity.

This isn't to say that naturally occurring systems cannot exhibit specified complexity or that material processes cannot serve as a conduit for specified complexity. Naturally occurring systems can exhibit specified complexity, and nature operating by purely material mechanisms 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 material causes) can generate specified complexity in the sense of originating it when previously there was none.

Take, for instance, a Rembrandt woodcut. It arose by mechanically impressing an inked woodblock on paper. The Rembrandt woodcut exhibits specified complexity. But the mechanical application of ink to paper via a woodblock does not account for the woodcut's specified complexity. 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 Rembrandt himself (in this case deliberately chiseling the woodblock). Specified complexity's causal chains end not with blind material forces but with a designing intelligence.

In Darwin's Black Box, biochemist Michael Behe connects specified complexity to biological design with his concept of irreducible complexity. Behe defines a system as irreducibly complex if it consists of several interrelated parts for which 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 faces grave obstacles in trying to account for such irreducibly complex systems. In No Free Lunch, I show how Behe's notion of irreducible complexity constitutes a special case of specified complexity and that irreducibly complex systems like the bacterial flagellum are therefore designed.

Accordingly, ID is more than simply the latest in a long line of design arguments. The related concepts of irreducible complexity and specified complexity render intelligent causes empirically detectable and make ID a full-fledged scientific theory, distinguishing it from the design arguments of philosophers and theologians, or what has traditionally been called "natural theology."

ID's chief claim is this: the world contains events, objects, and structures that exhaust the explanatory resources of undirected material causes and can be adequately explained by recourse to intelligent causes. Design theorists claim to demonstrate this rigorously. ID therefore takes a long-standing philosophical intuition and cashes it out as a scientific research program. This program depends on advances in probability theory, computer science, molecular biology, the philosophy of science, and the concept of information-to name but a few. Whether this program can turn design into an effective conceptual tool for investigating and understanding the natural world is for now the big question confronting science.

For more on ID, visit the following websites: www.designinference.com (which houses many of my writings on ID), www.ideacenter.org (the Intelligent Design and Evolution Awareness Center -- a clearinghouse for college and university students interested in ID), www.idurc.org (Intelligent Design Undergraduate Research Center), www.arn.org (for purchasing all things ID related), www.iscid.org (the International Society for Complexity, Information, and Design), and www.discovery.org/csc (Discovery Institute's Center for Science and Culture).