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What Is Intelligent Design and How Should We Defend It?

Casey Luskin
Photo credit: Marin Tulard, via Unsplash.

Editor’s note: This article is an excerpt from a chapter in the newly released book The Comprehensive Guide to Science and Faith: Exploring the Ultimate Questions About Life and the Cosmos

The most common objection to ID is that it is not science, but religion. To understand why this objection is flawed, we must first appreciate how ID theorists argue for design.

Intelligent design is a scientific theory that holds that many features of the universe and living things are best explained by an intelligent cause rather than an undirected process like natural selection. ID aims to discriminate between objects generated by material mechanisms and those caused by intelligence. 

Studying Human Agents

ID theorists start by observing how intelligent agents act when they design things. By studying human intelligent agents, we learn that when intelligent agents act, they generate high levels of information. The type of information that indicates design is generally called specified complexity, or complex and specified information (CSI for short). Let’s briefly discuss this term.

Roughly speaking, something is complex if it is unlikely. But complexity or unlikelihood alone is not enough to infer design. To see why, imagine that you are dealt a five-card hand for a poker game. Whatever hand you receive is going to be very unlikely. Even if you get a good hand, like a straight or a royal flush, you’re not necessarily going to say, “Aha! The deck was stacked.” Why? Because unlikely things happen all the time. We don’t infer design simply because of something’s being unlikely. We need more — according to ID theorist William Dembski, that is specification. Something is specified if it matches an independent pattern.

To understand specification, imagine you are a tourist visiting the mountains of North America. First, you come across Mount Rainier, a huge, dormant volcano in the Pacific Northwest. This mountain is unique; in fact, if all possible combinations of rocks, peaks, ridges, gullies, cracks, and crags are considered, its exact shape is extremely unlikely and complex. But you don’t infer design simply because Mount Rainier has a complex shape. Why? Because you can easily explain its shape through the natural processes of erosion, uplift, heating, cooling, freezing, thawing, weathering, etc. There is no special, independent pattern to the shape of Mount Rainier. Its complexity alone is not enough to infer design.

Now you visit a different mountain — Mount Rushmore in South Dakota. This mountain also has a very unlikely shape, but its shape is special. It matches a pattern — the faces of four famous Presidents. With Mount Rushmore, you don’t just observe complexity; you also find specification. Thus, you would infer that its shape was designed (Figure 1).

Figure 1. Which of these two mountains has a shape that allows us to detect design? Mount Rainier (left) has an unlikely (complex) shape, but it’s not specified, so we do not detect design. In contrast, Mount Rushmore (right) has a shape that is both complex and specified, so we detect design. Credits: Mount Rainier: Casey Luskin. Mount Rushmore: Dean Franklin, CC BY 2.0 (https://creativecommons.org/licenses/by/2.0), via Wikimedia Commons.

 Using the Scientific Method

We can further see that ID is science and not religion because ID uses the scientific method to make its claims. The scientific method is commonly described as a four-step process involving observation, hypothesis, experiment, and conclusion. ID uses this precise method:

  • Observations: ID theorists begin by observing that intelligent agents produce high levels of CSI. 
  • Hypothesis: ID theorists hypothesize that if a natural object was designed, it will contain high CSI. 
  • Experiment: Scientists perform experimental tests upon natural objects to determine if they contain high CSI. For example, mutational sensitivity tests show enzymes are rich in CSI: they contain highly unlikely orderings of amino acids that match a precise sequence-pattern that is necessary for function.1 Another easily testable form of CSI is irreducible complexity, wherein a system requires a certain core set of interacting parts to function. Genetic knockout experiments show that some molecular machines are irreducibly complex.2
  • Conclusion: When ID researchers find high CSI in DNA, proteins, and molecular machines, they conclude that such structures were designed.

Much Broader than Biology         

Contrary to popular conceptions, however, ID is much broader than biology. The laws of physics and chemistry show evidence of design because they are finely tuned to allow life to exist (see chapters 20, 21, 22, 23 for details). Universal laws are complex in that they exhibit unlikely settings — cosmologists have calculated that our universe is incredibly finely tuned for life to less than one part in 1010^123.3 (That’s 1 in 10 raised to the exponent of 10123; we don’t even have words or analogies to convey numbers this small!) Yet these laws are specified because they match an extremely narrow band of values and settings required for the existence of advanced life. This again is high CSI, and it indicates design. As Nobel laureate Charles Townes observed:

Intelligent design, as one sees it from a scientific point of view, seems to be quite real. This is a very special universe: it’s remarkable that it came out just this way. If the laws of physics weren’t just the way they are, we couldn’t be here at all.4

One Known Source

To summarize, scientific discoveries of the past century have shown life is fundamentally based upon:

  • A vast amount of CSI digitally encoded in a biochemical language in our DNA.
  • A computer-like system of information processing where cellular machinery reads, interprets, and executes the commands programmed into DNA to produce functional proteins. 
  • Irreducibly complex molecular machines composed of finely tuned proteins.
  • Exquisite fine-tuning of universal laws and constants.

Where, in our experience, do language-based digital code, computer-like programming, machines, and other high CSI structures come from? They have only one known source: intelligence. 

The argument for design briefly sketched here is entirely empirically based. It offers positive evidence for design by finding, in nature, the types of information and complexity that we know, from experience, derive from intelligent causes. (This positive case for design is further elaborated in chapter 16.) One might disagree with the conclusions of ID, but one cannot reasonably claim that this argument is based upon religion, faith, or politics. It’s based upon science. 


  1. Douglas D. Axe, “Extreme Functional Sensitivity to Conservative Amino Acid Changes on Enzyme Exteriors,” Journal of Molecular Biology, 301 (2000), 585-595; Douglas D. Axe, “Estimating the Prevalence of Protein Sequences Adopting Functional Enzyme Folds,” Journal of Molecular Biology 341 (2004), 1295-1315.
  2. Transcript of testimony of Scott Minnich, Kitzmiller v. Dover (M.D. Pa., PM Testimony, November 3, 2005), 103-112; Robert M. Macnab, “Flagella,” in Escherichia Coli and Salmonella Typhimurium: Cellular and Molecular Biology, Vol. 1, eds. Neidhardt et al. (Washington, DC: American Society for Microbiology, 1987), 73-74.
  3. Roger Penrose and M. Gardner, The Emperor’s New Mind: Concerning Computers, Minds, and the Laws of Physics(Oxford, UK: Oxford University Press, 2002).
  4. Bonnie Azab Powell, “‘Explore as much as we can’: Nobel Prize winner Charles Townes on evolution, intelligent design, and the meaning of life,” UC Berkeley News Center (June 17, 2005), https://www.berkeley.edu/news/media/releases/2005/06/17_townes.shtml (accessed October 26, 2020).