Irreducible complexity (IC) is the argument that certain biological systems with multiple interacting parts would not function if one of the parts were removed, so supposedly could not have evolved by successive small modifications from earlier less complex systems through natural selection, which would need all intermediate precursor systems to have been fully functional. This negative argument is then complemented by the claim that the only alternative explanation is a "purposeful arrangement of parts" inferring design by an intelligent agent. Irreducible complexity has become central to the creationist concept of intelligent design (ID), but the concept of irreducible complexity has been rejected by the scientific community at large,"We therefore find 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." 4:Whether ID Is Science, in E. Application of the Endorsement Test to the ID Policy, Ruling, Judge John E. Jones III, Kitzmiller v. Dover Area School District which regards intelligent design as pseudoscience."True in this latest creationist variant, advocates of so-called intelligent design ... use more slick, pseudoscientific language. They talk about things like "irreducible complexity" "for most members of the mainstream scientific community, ID is not a scientific theory, but a creationist pseudoscience."Mark D. Decker. College of Biological Sciences, General Biology Program, University of Minnesota "The Discovery Institute and ID proponents have a number of goals that they hope to achieve using disingenuous and mendacious methods of marketing, publicity, and political persuasion. They do not practice real science because that takes too long, but mainly because this method requires that one have actual evidence and logical reasons for one's conclusions, and the ID proponents just don't have those. If they had such resources, they would use them, and not the disreputable methods they actually use."See also list of scientific societies explicitly rejecting intelligent design Irreducible complexity and specified complexity are the two main arguments used by intelligent-design proponents to support their version of the theological argument from design.
The central concept that complex biological systems which require all their parts to function could not evolve by the incremental changes of natural selection, and so must have been produced by an intelligence, was already featured in creation science. "The biochemist Michael Behe contends that intelligence is required to produce irreducibly complex cellular structures (ones that couldn't function if a single part were removed) because such structures could not have been produced by the incremental additions of natural selection (Behe 1996). ... More important than whether irreducibly complex structures actually occur other than by definition, however, is the critical question of whether they can be produced by natural mechanisms. Behe answers no, claiming that natural selection, the main mechanism of evolutionary change, is inadequate to the task. He views natural selection as assembling a complex structure by stringing together components one at a time, with each addition requiring a selective advantage. .... Behe's idea of irreducible complexity was anticipated in creation science; much as in Paley's conception, creation science proponents hold that structures too complex to have occurred 'by chance' require special creation." The 1989 school textbook Of Pandas and People introduced the alternative terminology of intelligent design, a revised section in the 1993 edition of the textbook argued that a blood-clotting system demonstrated this concept., p. 145; "In fact, having a primitive, poorly controlled clotting system would probably be more dangerous to an animal, and therefore less advantageous, than no having no such system at all! Thus the clotting system cannot have emerged piecemeal. Like a car or a sentence, it requires the cooperative interaction of pre-existing components to work."
This section was written by Michael Behe, a professor of biochemistry at Lehigh University. He subsequently introduced the expression irreducible complexity along with a full account of his arguments, in his 1996 book Darwin's Black Box, and said it made evolution through natural selection of random mutations impossible, or extremely improbable. (originally published 1996). This was based on the mistaken assumption that evolution relies on improvement of existing functions, ignoring how complex adaptations originate from changes in function, and disregarding published research. Evolutionary biologists have published rebuttals showing how systems discussed by Behe can evolve.
In the 2005 Kitzmiller v. Dover Area School District trial, Behe gave testimony on the subject of irreducible complexity. The court found 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."
Definitions Michael Behe defined irreducible complexity in natural selection in terms of well-matched parts in his 1996 book Darwin's Black Box: ... a single system 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.
A second definition given by Behe in 2000 (his "evolutionary definition") states: An irreducibly complex evolutionary pathway is one that contains one or more unselected steps (that is, one or more necessary-but-unselected mutations). The degree of irreducible complexity is the number of unselected steps in the pathway.In Defense of the Irreducibility of the Blood Clotting Cascade: Response to Russell Doolittle, Ken Miller and Keith Robison, July 31, 2000, Discovery Institute article
Intelligent-design advocate William A. Dembski assumed an "original function" in his 2002 definition: A system performing a given basic function is irreducibly complex if it includes a set of well-matched, mutually interacting, nonarbitrarily individuated parts such that each part in the set is indispensable to maintaining the system's basic, and therefore original, function. The set of these indispensable parts is known as the irreducible core of the system.
History
Forerunners The argument from irreducible complexity is a descendant of the teleological argument for God (the argument from design or from complexity). This states that complex functionality in the natural world which looks designed is evidence of an intelligent creator. William Paley famously argued, in his 1802 watchmaker analogy, that complexity in nature implies a God for the same reason that the existence of a watch implies the existence of a watchmaker. This argument has a long history, and one can trace it back at least as far as Cicero's De Natura Deorum ii.34,On the Nature of the Gods, translated by Francis Brooks, London: Methuen, 1896.See Henry Hallam Introduction to the Literature of Europe in the Fifteenth, Sixteenth, and Seventeenth Centuries Boston: Little, Brown and Company, 1854 volume 2 page 385 part iii chapter iii section i paragraph 26 footnote u written in 45 BC.
Up to the 18th century
Galen (1st and 2nd centuries AD) wrote about the large number of parts of the body and their relationships, which observation was cited as evidence for creation.De Formatione Foetus=The Construction of the Embryo, chapter 11 in Galen: Selected Works, translated by P. N. Singer, The World's Classics, Oxford, Oxford University Press, 1997 . One 18th-century reference to Galen is David Hume Dialogues Concerning Natural Religion, 1779, Part 12, § 3, page 215. Also see Galen's De Usu Partium=On the Usefulness of the Parts of the Body, translated and edited by Margaret Tallmadge May, Ithaca, New York, Cornell University Press, 1968, especially book XVII. For a relevant discussion of Galen and other ancients see pages 121–122, The idea that the interdependence between parts would have implications for the origins of living things was raised by writers starting with Pierre Gassendi in the mid-17th centuryDe Generatione Animalium, chapter III. Partial translation in: Howard B. Adelmann, Marcello Malpighi and the Evolution of Embryology Ithaca, New York, Cornell University Press, 1966, volume 2, pages 811-812. and by John Wilkins (1614–1672), who wrote (citing Galen), "Now to imagine, that all these things, according to their several kinds, could be brought into this regular frame and order, to which such an infinite number of Intentions are required, without the contrivance of some wise Agent, must needs be irrational in the highest degree."John Wilkins, Of the Principles and Duties of Natural Religion, London, 1675, book I, chapter 6, page 82 Early English Books Online"The appeal to irreducible complexity goes back more than three centuries. To quote John Wilkins ...", Paul Braterman "Darwin Does Devolve. Sometimes. So What?" 3 Quarks Daily February 25, 2019 In the late 17th-century, Thomas Burnet referred to "a multitude of pieces aptly joyn'd" to argue against the eternity of life.The Sacred Theory of the Earth , 2nd edition, London: Walter Kettilby, 1691. Book I Chapter IV page 43 In the early 18th century, Nicolas Malebranche Livre 6ième, 2ième partie, chapître 4; English translation: Second paragraph from the end of the chapter, on page 465. wrote "An organized body contains an infinity of parts that mutually depend upon one another in relation to particular ends, all of which must be actually formed in order to work as a whole", arguing in favor of preformation, rather than epigenesis, of the individual;Pages 202-204 of and a similar argument about the origins of the individual was made by other 18th-century students of natural history. In his 1790 book, The Critique of Judgment, Kant is said by Guyer to argue that "we cannot conceive how a whole that comes into being only gradually from its parts can nevertheless be the cause of the properties of those parts".This is Guyer's exposition on page 22 of Guyer adds this parenthetical comment: "(here is where the theory of natural selection removes the difficulty)". See Kant's discussion in section IX of the "First Introduction" to the Critique of Judgment and in §§ 61, 64 (where he uses the expression wechselsweise abhängt="reciprocally dependent"), and § 66 of "Part Two, First Division". For example, German original See also German original
19th century Chapter XV of Paley's Natural Theology discusses at length what he called "relations" of parts of living things as an indication of their design.William Paley:Natural Theology; or, Evidences of the Existence and Attributes of the Deity. Collected from the Appearances of Nature 12th edition, 1809
Georges Cuvier applied his principle of the correlation of parts to describe an animal from fragmentary remains. For Cuvier, this related to another principle of his, the conditions of existence, which excluded the possibility of transmutation of species.See especially chapters VI and VII of See also the discussion of these principles in the Wikipedia article on Cuvier.