What Is Intelligent Design?

Intelligent design is the claim that some features of living things and of the universe are best explained by an intelligent cause rather than by an undirected process such as natural selection. Its supporters present it as a scientific theory. Most scientists regard it as a modern form of the old argument from design, and in 2005 a United States federal court ruled that it is not science and could not be taught as science in a public school. This guide explains what intelligent design says, where it came from, its two main arguments, how scientists respond, and why the debate matters.

Intelligent Design at a Glance

Question	Short answer
What does it claim?	Some natural features are best explained by an intelligent cause, not by natural selection
Who promotes it?	Mainly the Discovery Institute in Seattle and writers associated with it
Main arguments	Irreducible complexity (Michael Behe, 1996) and specified complexity (William Dembski, 1998)
Older roots	The design argument, made famous by William Paley’s watchmaker in 1802
Legal status in US schools	Ruled not science in Kitzmiller v. Dover, 20 December 2005
Scientific standing	Rejected by most biologists, who see evolution as well supported by evidence

What Intelligent Design Claims

The Discovery Institute, the organisation most closely linked to the movement, defines the theory of intelligent design as the view that certain features of the universe and of living things are best explained by an intelligent cause rather than an undirected process such as natural selection. Supporters usually say that the theory does not name the designer and that it is a conclusion drawn from evidence, not from scripture. Many of them accept that the Earth is billions of years old, which separates them from young-Earth creationists, and some accept that species share common ancestors. What they deny is that unguided natural processes are enough to explain the complexity of life.

Critics reply that an explanation which never says who the designer is, how the design was carried out or when it happened makes no predictions that could be tested. They also point out that most leading supporters of intelligent design are religious believers who identify the designer with God, and that the movement’s materials have often been written for use in schools.

Where Intelligent Design Came From

The idea that nature shows signs of design is very old. Its best-known statement is William Paley’s Natural Theology, published in 1802. Paley imagined finding a watch on the ground. A stone needs no special explanation, he argued, but the parts of a watch fit together so precisely for a purpose that we would conclude it had a maker, and living things show the same kind of fitting together. The argument and its weaknesses are discussed in more detail in the watchmaker argument.

Even before Paley, David Hume’s Dialogues Concerning Natural Religion, published in 1779, had raised objections that are still used today: that the universe looks more like a living organism than a machine, and that design reasoning at best points to a limited designer rather than the God of any particular religion. In 1859 Charles Darwin offered a natural mechanism, natural selection, that could produce the appearance of design without a designer. Intelligent design in its modern form emerged in the late twentieth century as an attempt to restate the design argument in the language of biochemistry, information theory and cosmology.

Irreducible Complexity

The biochemist Michael Behe introduced the idea of irreducible complexity in his 1996 book Darwin’s Black Box. A system is irreducibly complex, in Behe’s sense, if it is made of several interacting parts and stops working when any one of them is removed. Behe argued that such systems could not have been built up gradually by natural selection, because the earlier, incomplete versions would have been useless. His best-known example is the bacterial flagellum, a tail-like structure that some bacteria use to swim.

Biologists answer that evolution does not have to build a system by adding its parts one at a time for the same job. Parts often evolve for one function and are later borrowed for another, and a simpler version of a structure can still be useful. In the common example, half an eye still detects light, and half a flagellum still aids movement or secretion. Researchers have identified proteins related to parts of the flagellum that do other jobs in other bacteria, which suggests possible routes by which it could have evolved.

Specified Complexity

The mathematician and philosopher William Dembski developed a second argument in his 1998 book The Design Inference. He argued that design can be detected when something is both highly improbable and matches an independent pattern, which he called specified complexity. A long string of random letters is improbable but meaningless; a sonnet is improbable and also matches the patterns of language. Dembski claimed that the information in DNA has this property and so points to an intelligent source.

Critics, including mathematicians and biologists, argue that the method assumes what it sets out to prove. To call a biological structure improbable, you need to know the probability of every natural route that could have produced it, and that is exactly the question in dispute. They also note that natural selection is not a random process in the sense the argument requires: variation is random, but which variations survive is not.

How Scientists Respond

The main scientific objection is that intelligent design is not testable in the way a scientific theory must be. A theory earns its place by making predictions that could turn out wrong. Evolution predicts, for example, the order in which fossils appear in rock layers, the pattern of shared genes between species, and the existence of intermediate forms, and on that last point transitional forms are abundant. Intelligent design, critics say, can accommodate any observation, because a designer of unknown abilities and motives could have done anything.

Scientists also point to features that look poorly designed, such as the human eye’s blind spot or the long detour of the nerve that runs from the brain to the larynx, which make sense as the products of gradual change from earlier forms. Geology tells a similar story: evidence such as seashells found high on mountains is explained by the slow movement of the Earth’s crust over the immense age of the Earth. Supporters of intelligent design reply that apparent flaws may have purposes not yet understood, and that a designer need not produce perfect results.

Underlying the dispute is a question about what science is. Most scientists hold that science looks for natural explanations because those are the ones that can be tested, and that evolution is not a belief at all; it is an explanation tested against the evidence. Some supporters of intelligent design argue that this rule unfairly excludes design before the evidence is considered.

Intelligent Design in Court: Kitzmiller v. Dover

The most important legal test came in Pennsylvania. In October 2004 the Dover Area School Board adopted a policy that presented intelligent design as an alternative to evolution in high school biology, and pointed students to the intelligent design textbook Of Pandas and People. Eleven parents sued the school district. On 20 December 2005 Judge John E. Jones III of the United States District Court for the Middle District of Pennsylvania ruled in their favour in Kitzmiller v. Dover Area School District.

In a 139-page opinion, the judge addressed directly whether intelligent design is science and concluded that it is not, and that it cannot separate itself from its creationist and religious roots. He found that the board members had acted from religious motives and that the policy violated the Establishment Clause of the United States Constitution. Supporters of intelligent design criticised the ruling as the work of an activist judge, a charge the judge anticipated and rejected in the opinion itself. The ruling is binding only in that district, but it has been widely cited in the debate ever since.

Intelligent Design and Religion

Intelligent design is not the same as religious belief in a creator. Many religious people, including many scientists, accept evolution fully and see no conflict with their faith. Some see God as working through natural processes rather than intervening at particular points. Others find the design argument persuasive in a broader form, for example the claim that the physical constants of the universe appear fine-tuned for life, while rejecting the biological claims of intelligent design. The fine-tuning argument is a separate debate, with its own responses such as the anthropic principle and the idea of a multiverse.

Frequently Asked Questions

Is intelligent design the same as creationism?

Not exactly. Traditional creationism usually starts from a literal reading of Genesis, while intelligent design avoids naming the designer or appealing to scripture. Critics, and the court in Kitzmiller v. Dover, concluded that it grew out of creationism and shares its religious purpose.

Is intelligent design a scientific theory?

Its supporters say it is. Most scientists say it is not, because it makes no testable predictions and does not propose a mechanism. A federal court reached the same conclusion in 2005.

Who started the intelligent design movement?

The modern movement grew in the 1990s around writers such as the biochemist Michael Behe and the mathematician William Dembski, and it has been promoted mainly by the Discovery Institute. Its ideas build on much older design arguments, especially William Paley’s.

Can intelligent design be taught in schools?

In the United States, the 2005 Dover ruling found that teaching it as science in a public school violated the Constitution. It can be discussed in courses on religion, philosophy or the history of ideas.

Summary

Intelligent design holds that some features of life and the universe are best explained by an intelligent cause. Its main arguments, irreducible complexity and specified complexity, restate the older design argument in modern scientific terms. Most biologists reject it because it makes no testable predictions and because evolution explains the same features with a well-supported natural mechanism, and a federal court ruled in 2005 that it is not science. Supporters continue to argue that science should be open to design as an explanation. For the wider debate about whether a designer or creator exists, see is God real?

Sources

• Discovery Institute, “Intelligent Design: Frequently Asked Questions”. discovery.org.
• Stanford Encyclopedia of Philosophy, “Teleological Arguments for God’s Existence”. plato.stanford.edu.
• William Paley, Natural Theology (1802).
• David Hume, Dialogues Concerning Natural Religion (1779).
• Michael Behe, Darwin’s Black Box (1996).
• William Dembski, The Design Inference (1998).
• Kitzmiller v. Dover Area School District, United States District Court for the Middle District of Pennsylvania, 20 December 2005.
• American Civil Liberties Union, “ACLU Hails Historic Ruling in Dover, Pennsylvania ‘Intelligent Design’ Case” (20 December 2005). aclu.org.