Also known as the "Teleological" (about the ends or purposes) argument. Intelligent design (ID) is a family of religious arguments for the existence of God, presented by its proponents as an evidence-based theory of life, the physical constants that allow for it, or any other such aspect of reality that looks as though it had been purposefully designed.
The underlying idea is that reality or certain aspects of it look as though they had been made with a purpose in mind. Living organisms were often cited as an example of design in nature before Darwin came up with a scientific explanation. In recent times theologians have chiefly moved on to modern physics, where certain cosmological constants appear to be "fine tuned" to allow for life to exist. Rejection to biological evolution remains popular among fundamentalist circles, however. ID presents two main arguments against evolutionary explanations: irreducible complexity and specified complexity. These arguments assert that certain features (biological and informational, respectively) are too complex to be the result of natural processes. As a positive argument against evolution, ID proposes an analogy between natural systems and human artifacts, a version of the theological argument from design for the existence of God. ID proponents then conclude by analogy that the complex features, as defined by ID, are evidence of design. Irreducible Complexity: The term "irreducible complexity" was introduced by biochemist Michael Behe in his 1996 book Darwin's Black Box. Behe defines it as "a single system which is composed of several well-matched interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning". Behe uses the analogy of a mousetrap to illustrate this concept. A mousetrap consists of several interacting pieces—the base, the catch, the spring and the hammer—all of which must be in place for the mousetrap to work. Removal of any one piece destroys the function of the mousetrap. Intelligent design advocates assert that natural selection could not create irreducibly complex systems, because the selectable function is present only when all parts are assembled. Behe argued that irreducibly complex biological mechanisms include the bacterial flagellum of E. coli, the blood clotting cascade, cilia, and the adaptive immune system. Specified Complexity: The intelligent design concept of "specified complexity" was developed in the 1990s by mathematician, philosopher, and theologian William A. Dembski. Dembski states that when something exhibits specified complexity (i.e., is both complex and "specified", simultaneously), one can infer that it was produced by an intelligent cause (i.e., that it was designed) rather than being the result of natural processes. He provides the following examples: "A single letter of the alphabet is specified without being complex. A long sentence of random letters is complex without being specified. A Shakespearean sonnet is both complex and specified." He states that details of living things can be similarly characterized, especially the "patterns" of molecular sequences in functional biological molecules such as DNA.
Intelligent Design is dismissed as a "pseudo-science" - a form of creationism that lacks empirical support and offers no testable or tenable hypotheses, so is not science. Detailed scientific examination has rebutted the claims that evolutionary explanations are inadequate, and this premise of intelligent design—that evidence against evolution constitutes evidence for design—is a false dichotomy. It is asserted that ID challenges the methodological naturalism inherent in modern science though proponents concede that they have yet to produce a scientific theory. Critique of Fine-tuning of Cosmological Constants: The argument presupposes intelligent beings could not come about from material arrangements other than carbon-based biology. Since cosmological constants are within a highly-improbable range only for life as we know it, it is not valid to extrapolate to the probability that intelligent minds of any sort would occur naturally. If the Multiverse hypothesis of quantum mechanics is true, then there is no need to explain the uncanny anthropic tuning of our Universe. All possible Universes exist with equal probability and we just happen to be one of the few where intelligent life forms. Finally, the Universe remains largely inhospitable. Some constants such as the amount of entropy in the early Universe are very far from being advantageous for life formation. An intelligent God could have made an even better job at designing a Universe for humans to proliferate. Critique of Irreducible Complexity: Critics point out that the irreducible complexity argument assumes that the necessary parts of a system have always been necessary and therefore could not have been added sequentially. They argue that something that is at first merely advantageous can later become necessary as other components change. Furthermore, they argue, evolution often proceeds by altering preexisting parts or by removing them from a system, rather than by adding them. This is sometimes called the "scaffolding objection" by an analogy with scaffolding, which can support an "irreducibly complex" building until it is complete and able to stand on its own. Behe has acknowledged using "sloppy prose", and that his "argument against Darwinism does not add up to a logical proof." Irreducible complexity has remained a popular argument among advocates of intelligent design; in the Dover trial, the court held that "Professor Behe's claim for irreducible complexity has been refuted in peer-reviewed research papers and has been rejected by the scientific community at large." Critique of Specified Complexity: The conceptual soundness of Dembski's specified complexity/CSI argument has been discredited in the scientific and mathematical communities. Specified complexity has yet to be shown to have wide applications in other fields, as Dembski asserts. John Wilkins and Wesley R. Elsberry characterize Dembski's "explanatory filter" as eliminative because it eliminates explanations sequentially: first regularity, then chance, finally defaulting to design. They argue that this procedure is flawed as a model for scientific inference because the asymmetric way it treats the different possible explanations renders it prone to making false conclusions. Richard Dawkins, another critic of intelligent design, argues in The God Delusion (2006) that allowing for an intelligent designer to account for unlikely complexity only postpones the problem, as such a designer would need to be at least as complex. Other scientists have argued that evolution through selection is better able to explain the observed complexity, as is evident from the use of selective evolution to design certain electronic, aeronautic and automotive systems that are considered problems too complex for human "intelligent designers".