Editing Irreducible complexity (section)

== 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.<ref name="paley" /> This argument has a long history, and one can trace it back at least as far as [[Cicero]]'s ''[[De Natura Deorum]]'' ii.34,<ref>''On the Nature of the Gods'', translated by Francis Brooks, London: Methuen, 1896.</ref><ref>See [[Henry Hallam]] [https://books.google.com/books?id=FpDzTASTVwsC&pg=PA385 ''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''</ref> 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.<ref>''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 {{ISBN|978-0-19-282450-9}}. One 18th-century reference to Galen is [http://www.anselm.edu/homepage/dbanach/dnr.htm#A13 David Hume ''Dialogues Concerning Natural Religion'', 1779, Part 12]{{webarchive|url=https://web.archive.org/web/20051122134556/http://www.anselm.edu/homepage/dbanach/dnr.htm |date=2005-11-22 }}, §&nbsp;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, {{cite book |author= Goodman, Lenn Evan |title= Creation and evolution |location= Milton Park, Abingdon, Oxon and New York |publisher= Routledge |year= 2010 |isbn= 978-0-415-91380-5}}</ref> 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 century<ref>''De 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.</ref> 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."<ref>John Wilkins, ''Of the Principles and Duties of Natural Religion'', London, 1675, book I, chapter 6, page 82 [https://quod.lib.umich.edu/e/eebo/A66053.0001.001/1:5.6?rgn=div2;view=fulltext Early English Books Online]</ref><ref>"The appeal to irreducible complexity goes back more than three centuries. To quote John Wilkins ...", [https://www.3quarksdaily.com/3quarksdaily/2019/02/darwin-does-devolve-sometimes-so-what.html Paul Braterman "Darwin Does Devolve. Sometimes. So What?" 3 Quarks Daily February 25, 2019]</ref> In the late 17th-century, [[Thomas Burnet (theologian)|Thomas Burnet]] referred to "a multitude of pieces aptly joyn'd" to argue against the [[eternity]] of life.<ref>[http://www.sacred-texts.com/earth/ste/ste07.htm ''The Sacred Theory of the Earth''] {{webarchive|url=https://web.archive.org/web/20071020060523/http://sacred-texts.com/earth/ste/ste07.htm |date=2007-10-20 }}, 2nd edition, London: Walter Kettilby, 1691. Book I Chapter IV page 43</ref> In the early 18th century, [[Nicolas Malebranche]]<ref>{{cite book|first= Nicolas|last= Malebranche|title= De la recherche de la verité: où l'on traite de la nature de l'esprit de l'homme, & de l'usage qu'il en doit faire pour éviter l'erreur dans les sciences|edition= 6ième|location= Paris|publisher= Chez Michel David|year= 1712|url= https://books.google.com/books?id=Gi0_AAAAcAAJ&q=%22d%C3%A9pendent%20mutuellement%22&pg=RA1-PA57}} Livre 6ième, 2ième partie, chapître 4; English translation: {{cite book|first= Nicholas|last= Malebranche|title= The Search After Truth: With Elucidations of The Search After Truth|editor1= Thomas M. Lennon |editor2= Paul J. Olscamp |location= Cambridge|publisher= Cambridge University Press|year= 1997|isbn= 978-0-521-58004-5|url= https://archive.org/details/searchaftertruth0000male|url-access= registration|page= [https://archive.org/details/searchaftertruth0000male/page/465 465]}} Second paragraph from the end of the chapter, on page 465.</ref> 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 (biology)|epigenesis]], of the individual;<ref>Pages 202-204 of {{cite book|first= Andrew |last= Pyle |chapter= Malebranche on Animal Generation: Preexistence and the Microscope |editor= Smith JH |title= The problem of animal generation in early modern philosophy |publisher= Cambridge University Press |location= Cambridge, UK |year= 2006 |pages= 194–214 |isbn= 978-0-521-84077-4 |chapter-url= https://books.google.com/books?id=EyMWhGH4JgIC&q=%22irreducible+complexity%22+intitle%3Aproblem+intitle%3Aof+intitle%3Ageneration+inauthor%3Asmith&pg=PA204|author-link= Andrew Pyle (philosopher) }}</ref> and a similar argument about the origins of the individual was made by other 18th-century students of natural history.<ref>{{cite web|url=http://talkreason.org/articles/chickegg.cfm|title=The Chicken or the Egg|website=talkreason.org|access-date=7 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170429075443/http://www.talkreason.org/articles/chickegg.cfm|archive-date=29 April 2017}}</ref> In his 1790 book, ''[[The Critique of Judgment#Teleology|The Critique of Judgment]]'', [[Immanuel Kant|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".<ref>This is Guyer's exposition on page 22 of {{cite book|editor= Paul Guyer|title= The Cambridge Companion to Kant|first= Paul|last= Guyer|author-link= Paul Guyer|chapter= Introduction|pages= [https://archive.org/details/cambridgecompani0000unse_i7u7/page/1 1–25]|location= Cambridge|publisher= Cambridge University Press|year= 1992|isbn= 978-0-521-36768-4|chapter-url= https://books.google.com/books?id=pYE5rVzrPNgC&q=%22gradually+from+its+parts%22+intitle%3Acambridge+intitle%3Acompanion+intitle%3Ato+intitle%3Akant+inauthor%3Aguyer&pg=PA22|url= https://archive.org/details/cambridgecompani0000unse_i7u7/page/1}} 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 §§&nbsp;61, 64 (where he uses the expression ''wechselsweise abhängt''="reciprocally dependent"), and §&nbsp;66 of "Part Two, First Division". For example, {{cite book |chapter-url= https://books.google.com/books?id=JEXHIcDbBDcC&q=%22reciprocally+dependent%22+intitle%3Acritique+intitle%3Ajudgment+inauthor%3Akant&pg=PA243 |title= Critique of the power of judgment |first= Immanuel |last= Kant |editor1= Paul Guyer |editor2= Eric Matthews |location= Cambridge |publisher= Cambridge University Press |year= 2000 |isbn= 978-0-521-34447-0 |pages= 243–244 |chapter= §&nbsp;64 }} German original {{cite book |title= Kritik der Urtheilskraft |url= https://books.google.com/books?id=6O1Nayo3wWgC&q=akademie+%22wechselsweise+abhängt%22+inauthor:kant&pg=PA371 |volume= 5 |page= 371 |location= Berlin |publisher= Georg Reimer |edition= Königlich Preußischen Akademie der Wissenschaften |series= Kants gesammelte Schriften |year= 1913 |isbn= 978-3-11-001438-9 }}</ref><ref>See also {{cite book|title=Opus Postumum|url=https://archive.org/details/opuspostumumthec00kant|url-access=limited|first=Imanuel|last=Kant|editor=Eckart Förster|translator1=Eckart Förster|translator2=Michael Rosen|location=Cambridge|publisher=Cambridge University Press|year=1993|isbn=0-521-31928-5|page=[https://archive.org/details/opuspostumumthec00kant/page/n125 64]|quote=The definition of an organic body is that it is a body, every part of which is there ''for the sake of the other'' (reciprocally as end and, at the same time, means).}}German original {{cite book |title= Kritik der Urtheilskraft |url= https://books.google.com/books?id=6O1Nayo3wWgC&q=akademie+%22wechselsweise+abhängt%22+inauthor:kant&pg=PA371 |volume= 21 |page= 210|location= Berlin |publisher= Georg Reimer |edition= Königlich Preußischen Akademie der Wissenschaften |series= Kants gesammelte Schriften |isbn=978-3-11-090167-2|date = February 1971}}</ref>

==== 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.<ref name="paley">[http://darwin-online.org.uk/content/frameset?itemID=A142&viewtype=text&pageseq=1 William Paley:''Natural Theology; or, Evidences of the Existence and Attributes of the Deity. Collected from the Appearances of Nature'' 12th edition, 1809] {{webarchive|url=https://web.archive.org/web/20080430030715/http://darwin-online.org.uk/content/frameset?itemID=A142&viewtype=text&pageseq=1 |date=2008-04-30 }}</ref>

[[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]].<ref>See especially chapters VI and VII of {{cite book|first= William |last= Coleman |title= Georges Cuvier, Zoologist: A Study in the History of Evolution Theory |url= https://archive.org/details/georgescuvierzoo0000cole |url-access= registration |location= Cambridge, Massachusetts |publisher= Harvard University Press |year= 1964}} See also the discussion of these principles in the Wikipedia article on [[Georges Cuvier|Cuvier]].</ref>

While he did not originate the term, [[Charles Darwin]] identified the argument as a possible way to falsify a prediction of the theory of evolution at the outset. In ''[[The Origin of Species]]'' (1859), he wrote, "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case."<ref>[[Charles Darwin|Darwin, Charles]] (1859). ''[[The Origin of Species|On the Origin of Species]]''. London: John Murray. [http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=207 page 189, Chapter VI] {{webarchive|url=https://web.archive.org/web/20070930011159/http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=207 |date=2007-09-30 }}</ref> Darwin's theory of evolution challenges the teleological argument by postulating an alternative explanation to that of an intelligent designer—namely, evolution by natural selection. By showing how simple unintelligent forces can ratchet up designs of extraordinary complexity without invoking outside design, Darwin showed that an intelligent designer was not the necessary conclusion to draw from complexity in nature. The argument from irreducible complexity attempts to demonstrate that certain biological features cannot be purely the product of Darwinian evolution.<ref>See for example, {{cite book|first= Alan R.|last= Rogers|author-link=Alan R. Rogers|title= The Evidence for Evolution|location= Chicago|publisher= University of Chicago Press|year= 2011|isbn= 978-0-226-72382-2}} in pages 37–38, 48–49 citing Joseph John Murphy accepting natural selection within limits, excepting "the eye" with its multiple parts. {{cite news|first= Joseph John |last=Murphy|title= Presidential Address to the Belfast Natural History and Philosophical Society|journal= Northern Whig|location= Belfast|date= November 19, 1866|url= http://darwin-online.org.uk/content/frameset?viewtype=image&itemID=CUL-DAR226.1.118-119&pageseq=1|url-status= live|archive-url= https://web.archive.org/web/20120718161404/http://darwin-online.org.uk/content/frameset?viewtype=image&itemID=CUL-DAR226.1.118-119&pageseq=1|archive-date= July 18, 2012}} and in page 48 citing {{cite book|first=C. |last=Pritchard|author-link=Charles Pritchard|title=The Continuity of the Schemes of Nature and Revelation: A Sermon Preached, by request, on the occasion of the meeting of the British Association at Nottingham. With remarks on some relations of modern knowledge to theology|chapter=Appendix Note A On the Origin of Species by Natural Selection|year=1866|pages=31–37|location=London|publisher=Bell and Daldy|chapter-url=https://archive.org/details/continuityofsche00prit}}, especially page 33</ref>

In the late 19th century, in a dispute between supporters of the adequacy of [[natural selection]] and those who held for [[inheritance of acquired characteristics]], one of the arguments made repeatedly by [[Herbert Spencer]], and followed by others, depended on what Spencer referred to as ''co-adaptation'' of ''co-operative'' parts, as in: <blockquote>"We come now to Professor [[August Weismann|Weismann]]'s endeavour to disprove my second thesis—that it is impossible to explain by natural selection alone the co-adaptation of co-operative parts. It is thirty years since this was set forth in 'The Principles of Biology.' In §&nbsp;166, I instanced the enormous horns of the extinct [[Irish elk]], and contended that in this and in kindred cases, where for the efficient use of some one enlarged part many other parts have to be simultaneously enlarged, it is out of the question to suppose that they can have all spontaneously varied in the required proportions."<ref>Page 594 in: {{cite journal|first= Herbert|last= Spencer|title= Weismannism Once More|journal= [[The Contemporary Review]]|date= October 1894|volume= 66 |pages= 592–608}} Another essay of Spencer's treating this concept is: {{cite journal|first= Herbert |last= Spencer |title= The Inadequacy of "Natural Selection" |journal= The Contemporary Review |volume= 63 |year= 1893 |pages= 153–166}} (Part I: February) and pages 439-456 (Part II: March). These essays were reprinted in {{cite book|first= Herbert|last= Spencer|title= The Works of Herbert Spencer|year= 1891|place= London|publisher= Williams and Norgate|volume= 17}} (also Osnabrück: Otto Zeller, 1967). See also part III, Chapter XII, §&nbsp;166, pages 449-457 in: {{cite book |first= Herbert |last= Spencer |title= Principles of Biology |year= 1864 |place= London |publisher= Williams and Norgate|volume= I}} And: {{cite journal|journal= [[The Nineteenth Century (periodical)|The Nineteenth Century]] |first= Herbert|last= Spencer|title= The Factors of Organic Evolution |volume= 19 |year= 1886 |pages= 570–589}} (Part I: April) and pages 749-770 (Part II: May). "Factors" was reprinted in pages 389-466 of {{cite book|first= Herbert|last= Spencer|title= The Works of Herbert Spencer|volume= 13|location= London|publisher= Williams and Norgate|year= 1891}} (also Osnabrück: Otto Zeller, 1967)= volume 1 of ''Essays: Scientific, Political, and Speculative''.</ref><ref>One example of a response was in Section III(γ) pages 32-42 of {{cite book|first= August |last= Weismann |chapter= The Selection theory |pages= 19–65 |title= Darwin and Modern Science: Essays in Commemoration of the Centenary of the Birth of Charles Darwin and of the Fiftieth Anniversary of the Publication of The Origin of Species|chapter-url= https://archive.org/details/in.ernet.dli.2015.42056 |editor= [[Albert Seward]]|location= Cambridge |publisher= Cambridge University Press |year= 1909}} See also Chapter VII, §&nbsp;12(1), pages 237-238 in: {{cite book|first= J. Arthur |last=Thomson|title= Heredity|url= https://archive.org/details/in.ernet.dli.2015.217008|place= London|publisher= John Murray|year= 1908|author-link= J. Arthur Thomson}} Both of these referred to what has become known as the [[Baldwin effect]]. An analysis of both sides of the issue is: {{cite book |first= George John |last=Romanes |title= Darwin and After Darwin: Post-Darwinian Questions, Heredity, Utility |volume= II |chapter= III: Characters as Hereditary and Acquired (continued) |pages= 60–102 |place= London |publisher= Longman, Green |year= 1895|author-link= George John Romanes }}</ref></blockquote> Darwin responded to Spencer's objections in chapter XXV of ''[[The Variation of Animals and Plants Under Domestication]]'' (1868).<ref>{{cite book|title= The Variation of Animals and Plants Under Domestication|first= Charles|last= Darwin|year= 1868|location= London|publisher= John Murray|chapter= XXV. Laws of Variation ''continued'' – Correlated Variability|volume= 2|pages= 321–338|chapter-url= http://darwin-online.org.uk/content/frameset?keywords=co%20ordinated&pageseq=236&itemID=F877.2&viewtype=text|url-status= live|archive-url= https://web.archive.org/web/20150925075611/http://darwin-online.org.uk/content/frameset?keywords=co%20ordinated&pageseq=236&itemID=F877.2&viewtype=text|archive-date= 2015-09-25}} especially page 333 and following.</ref> The history of this concept in the dispute has been characterized: "An older and more religious tradition of idealist thinkers were committed to the explanation of complex adaptive contrivances by intelligent design. ... Another line of thinkers, unified by the recurrent publications of Herbert Spencer, also saw [[co-adaptation]] as a composed, irreducible whole, but sought to explain it by the inheritance of acquired characteristics."<ref>Pages 67-68 in: {{cite journal|first= Mark|last= Ridley|title= Coadapatation and the Inadequacy of Natural Selection|journal= British Journal for the History of Science |volume= 15|issue= 1 |date= March 1982 |pages= 45–68 |doi= 10.1017/S0007087400018938|pmid= 11610981|s2cid= 9704653|author-link= Mark Ridley (zoologist)}}</ref>

[[St. George Jackson Mivart]] raised the objection to natural selection that "Complex and simultaneous co-ordinations ... until so far developed as to effect the requisite junctions, are useless".<ref>{{cite book|title= On the Genesis of Species|url= https://archive.org/details/Mivart1871gk14P|first= St. George Jackson |last=Mivart|location= London|publisher= Macmillan|year= 1871|page= [https://archive.org/details/Mivart1871gk14P/page/52 52]|author-link= St. George Jackson Mivart}}</ref> In the 2012 book ''Evolution and Belief, Confessions of a Religious Paleontologist'', Robert J. Asher said this "amounts to the concept of 'irreducible complexity' as defined by ... Michael Behe".<ref>{{cite book|author= Asher, Robert J.|title= Evolution and belief: confessions of a religious paleontologist|location= Cambridge & New York|publisher= Cambridge University Press|year= 2012|isbn= 978-0-521-19383-2|page= 214}} See also Christian Faculty Forum at [[University of California, Santa Barbara|UCSB]], [http://www.veritas-ucsb.org/library/origins/quotes/irreducible.html Irreducible Complexity] {{webarchive|url=https://web.archive.org/web/20111018165943/http://www.veritas-ucsb.org/library/origins/quotes/irreducible.html |date=2011-10-18 }} and the references cited there.</ref>

==== 20th century ====
[[Hermann Joseph Muller|Hermann Muller]], in the early 20th century, discussed a concept similar to irreducible complexity. However, far from seeing this as a problem for evolution, he described the "interlocking" of biological features as a consequence to be expected of evolution, which would lead to irreversibility of some evolutionary changes.<ref name="Muller_1918">{{cite journal |author= Muller, HJ |title= Genetic variability, twin hybrids and constant hybrids, in a case of balanced lethal factors |journal= Genetics |volume= 3 |issue= 5 |pages= 422–99 |year= 1918 |doi= 10.1093/genetics/3.5.422 |url= http://www.genetics.org/cgi/reprint/3/5/422 |pmid= 17245914 |pmc= 1200446 |url-status= dead |archive-url= https://web.archive.org/web/20070518220445/http://www.genetics.org/cgi/reprint/3/5/422 |archive-date= 2007-05-18 |access-date= 2006-10-31 }}, especially pages 463–4.</ref> He wrote, "Being thus finally woven, as it were, into the most intimate fabric of the organism, the once novel character can no longer be withdrawn with impunity, and may have become vitally necessary."<ref>{{cite journal |author= Muller, HJ |title= Reversibility in evolution considered from the standpoint of genetics |journal= Biological Reviews of the Cambridge Philosophical Society |volume= 14 |issue= 3 |pages= 261–80, quotation from 272 |year= 1939 |doi=10.1111/j.1469-185x.1939.tb00934.x |s2cid= 85668728 }}</ref>

In 1975 [[Thomas H. Frazzetta]] published a book-length study of a concept similar to irreducible complexity, explained by gradual, step-wise, non-teleological evolution. Frazzetta wrote: <blockquote>"A complex adaptation is one constructed of ''several'' components that must blend together operationally to make the adaptation 'work'. It is analogous to a machine whose performance depends upon careful cooperation among its parts. In the case of the machine, no single part can greatly be altered without changing the performance of the entire machine."</blockquote> The machine that he chose as an analog is the [[Peaucellier–Lipkin linkage]], and one biological system given extended description was the jaw apparatus of a python. The conclusion of this investigation, rather than that evolution of a complex adaptation was impossible, "awed by the adaptations of living things, to be stunned by their complexity and suitability", was "to accept the inescapable but not humiliating fact that much of mankind can be seen in a tree or a lizard."<ref>T. H. Frazzetta, ''Complex Adaptations in Evolving Populations'', Sunderland, Massachusetts: Sinauer Associates, 1975. {{ISBN|0-87893-194-5}}. Referencing pages 3, 4-7, 7-20, and xi, respectively.</ref>

In 1985 [[Graham Cairns-Smith|Cairns-Smith]] wrote of "interlocking": "How can a complex collaboration between components evolve in small steps?" and used the analogy of the scaffolding called [[centring|centering]]—used to [[arch#Construction|build an arch]] then removed afterwards: "Surely there was 'scaffolding'. Before the multitudinous components of present biochemistry could come to lean together ''they had to lean on something else.''"<ref name="Cairns-Smith, A. G. 1985 https://archive.org/details/sevencluestoorig00cair_0/page/39 39, 58–64">{{cite book |author= Cairns-Smith, A. G. |title= Seven clues to the origin of life: a scientific detective story |publisher= Cambridge University Press |location= Cambridge, UK |year= 1985 |pages= [https://archive.org/details/sevencluestoorig00cair_0/page/39 39, 58–64] |isbn= 978-0-521-27522-4 |url= https://archive.org/details/sevencluestoorig00cair_0/page/39 }}</ref><ref>McShea, Daniel W. and Wim Hordijk. "[https://link.springer.com/article/10.1007%2Fs11692-013-9227-6 Complexity by Subtraction]." ''Evolutionary Biology'' (April 2013). [http://www.worldwidewanderings.net/Professional/Publications/complsub.pdf PDF] {{webarchive|url=https://web.archive.org/web/20130513010713/http://www.worldwidewanderings.net/Professional/Publications/complsub.pdf |date=2013-05-13 }}.</ref> However, neither Muller or Cairns-Smith claimed their ideas as evidence of something supernatural.<ref name="Perakh 2008">{{cite journal |url= http://www.skeptic.com/the_magazine/ |title= Bacteria Flagella Look Like Man-made Machines |first= Mark |last= Perakh |publisher= [[Skeptic (U.S. magazine)]] |year= 2008 |volume= 14 |issue= 3 |access-date= 2008-12-06 |url-status= dead |archive-url= https://web.archive.org/web/20081208185535/http://www.skeptic.com/the_magazine/ |archive-date= 2008-12-08 |author-link= Mark Perakh }}</ref>

An early concept of irreducibly complex systems comes from [[Ludwig von Bertalanffy]] (1901–1972), an Austrian biologist.<ref>Ludwig von Bertalanffy (1952). ''Problems of Life: An Evaluation of Modern Biological and Scientific Thought, pg 148'' {{ISBN|1-131-79242-4}}</ref> He believed that complex systems must be examined as complete, [[irreducibility|irreducible]] systems in order to fully understand how they work. He extended his work on biological complexity into a general theory of systems in a book titled ''[[systems theory|General Systems Theory]]''.

After [[James Watson]] and [[Francis Crick]] published the structure of [[DNA]] in the early 1950s, General Systems Theory lost many of its adherents in the physical and biological sciences.<ref>{{cite book |author= Monod, Jacques |title= Chance and necessity: an essay on the natural philosophy of modern biology |publisher= Vintage Books |location= New York |year= 1972 |isbn= 978-0-394-71825-5 |url= https://archive.org/details/chancenecessity00mono }}</ref>
However, [[systems theory]] remained popular in the social sciences long after its demise in the physical and biological sciences.

===Creationism===
Versions of the irreducible complexity argument have been common in [[young Earth creationism|young Earth creationist]] (YEC) [[creation science]] journals. For example, in the July 1965 issue of [[Creation Research Society]] Quarterly [[Harold W. Clark]] described the complex interaction in which [[Prodoxidae|yucca moths]] have an "inherited action pattern" or instinct to fertilize plants: "Before the pattern can be inherited, it must be formed. But how could yucca plants mature seeds while waiting for the moths to learn the process and set the pattern? The whole procedure points so strongly to intelligent design that it is difficult to escape the conclusion that the hand of a wise and beneficent Creator has been involved." Similarly, honeybees pollinate apple blossom: "Again we may well ask how such an arrangement could have come about by accident, or how either the flowers or the bees could have survived alone. Intelligent design is again evident."<ref name="bio design classrooms" /><ref name="CRSQ 1965 2 2">{{cite web | title=CRSQ 1965 Volume 2, Number 2 | website=Creation Research Society | date=July 1965 | url=https://www.creationresearch.org/crsq-1965-volume-2-number-2 | access-date=29 November 2022|quote=The Plants Will Teach You}}</ref>

In 1974 the YEC [[Henry M. Morris]] introduced an irreducible complexity concept in his creation science book ''Scientific Creationism'', in which he wrote; "The creationist maintains that the degree of complexity and order which science has discovered in the universe could never be generated by chance or accident."{{sfn | Forrest | Gross | 2007 | pp=284–286}} He continued; "This issue can actually be attacked quantitatively, using simple principles of mathematical probability. The problem is simply whether a complex system, in which many components function unitedly together, and in which each component is uniquely necessary to the efficient functioning of the whole, could ever arise by random processes."<ref name="incoherence" /><ref>{{cite book |author= Morris, Henry |title= Scientific creationism |publisher= Creation-Life Publishers |location= San Diego, Calif |year= 1974 |page= [https://archive.org/details/scientificcreati00inst/page/59 59] |isbn= 978-0-89051-003-2 |edition= 2nd |author-link= Henry M. Morris |url= https://archive.org/details/scientificcreati00inst/page/59 }}</ref> In 1975 [[Duane Gish]] wrote in ''The Amazing Story of Creation from Science and the Bible''; "The creationist maintains that the degree of complexity and order which science has discovered in the universe could never be generated by chance or accident."{{sfn | Forrest | Gross | 2007 | pp=284–286}}

A 1980 article in the creation science magazine ''[[Creation Ministries International|Creation]]'' by the YEC [[Ariel A. Roth]] said "Creation and various other views can be supported by the scientific data that reveal that the spontaneous origin of the ''complex integrated biochemical systems'' of even the simplest organisms is, at best, a most improbable event".<ref name="incoherence" /> In 1981, defending the creation science position in the trial ''[[McLean v. Arkansas]]'', Roth said of "complex integrated structures": "This system would not be functional until all the parts were there ... How did these parts survive during evolution ...?"<ref>{{cite book |author1= Keough, Mark J. |author2= Geisler, Norman L. |title= The Creator in the courtroom "Scopes II": the 1981 Arkansas creation-evolution trial |publisher= Mott Media |location= Milford, Mich |year= 1982 |page= [https://archive.org/details/creatorincourtro00norm/page/146 146] |isbn= 978-0-88062-020-8 |url= https://archive.org/details/creatorincourtro00norm/page/146 }}</ref>

In 1985, countering the creationist claims that all the changes would be needed at once, [[Graham Cairns-Smith|Cairns-Smith]] wrote of "interlocking": "How can a complex collaboration between components evolve in small steps?" and used the analogy of the scaffolding called [[centring|centering]]—used to [[arch#Construction|build an arch]] then removed afterwards: "Surely there was 'scaffolding'. Before the multitudinous components of present biochemistry could come to lean together ''they had to lean on something else.''"<ref name="Cairns-Smith, A. G. 1985 https://archive.org/details/sevencluestoorig00cair_0/page/39 39, 58–64"/><ref>McShea, Daniel W. and Wim Hordijk. "[https://link.springer.com/article/10.1007%2Fs11692-013-9227-6 Complexity by Subtraction]." ''Evolutionary Biology'' (April 2013). [http://www.worldwidewanderings.net/Professional/Publications/complsub.pdf PDF] {{webarchive|url=https://web.archive.org/web/20130513010713/http://www.worldwidewanderings.net/Professional/Publications/complsub.pdf |date=2013-05-13 }}.</ref> Neither Muller or Cairns-Smith said their ideas were evidence of anything supernatural.<ref name="Perakh 2008"/>

The [[Flagellum|bacterial flagellum]] featured in creation science literature. Morris later claimed that one of their [[Institute for Creation Research]] "scientists (the late Dr. Dick Bliss) was using this example in his talks on creation a generation ago". In December 1992 the creation science magazine ''Creation'' called bacterial flagella "rotary engines", and dismissed the possibility that these "incredibly complicated arrangements of matter" could have "evolved by selection of chance mutations. The alternative explanation, that they were created, is much more reasonable."<ref name="bio design classrooms">{{cite journal | last1=Scott | first1=Eugenie C. | last2=Matzke | first2=Nicholas J. | title=Biological design in science classrooms | journal=Proceedings of the National Academy of Sciences | volume=104 | issue=suppl_1 | date=15 May 2007 | issn=0027-8424 | doi=10.1073/pnas.0701505104 | pages=8669–8676| pmid=17494747 | pmc=1876445 | bibcode=2007PNAS..104.8669S | doi-access=free }}</ref><ref name="creation Rotary engines">{{cite web | title=Rotary engines | website=creation.com | date=December 1992 | url=https://creation.com/rotary-engines |quote=''[[Creation Ministries International|Creation]]'' 15(1):23 | access-date=17 July 2023}}</ref> An article in the [[Creation Research Society]] Magazine for June 1994 called a flagellum a "bacterial nanomachine", forming the "bacterial rotor-flagellar complex" where "it is clear from the details of their operation that nothing about them works unless every one of their complexly fashioned and integrated components are in place", hard to explain by natural selection. The abstract said that in "terms of biophysical complexity, the bacterial rotor-flagellum is without precedent in the living world. ... To evolutionists, the system presents an enigma; to creationists, if offers clear and compelling evidence of purposeful intelligent design."<ref name="Slack 2008 p. 173">{{cite book | last=Slack | first=G. | title=The Battle Over the Meaning of Everything: Evolution, Intelligent Design, and a School Board in Dover, PA | publisher=Wiley | year=2008 | isbn=978-0-470-37931-8 | url=https://books.google.com/books?id=1kpx8HrQ08cC&pg=PA173 | access-date=17 July 2023 | pages=172–173 |quote=an article, predating [the 1996] publication of Darwin's Black Box, the book by Michael Behe in which the idea of 'irreducible complexity' was allegedly hammered out and from which the bacterial flagellum became the molecular poster child for both irreducible complexity and intelligent design. The article, titled 'Not So Blind a Watchmaker,' is in a journal called Creation ''Research Society Quarterly'', an overtly creationist journal published by the Creation Research Societv. .... a picture of none other than our now old friend the bacterial flagellum, accompanied by text that calls it a 'nanomachine,' which sounds a lot like biological machine, and a description that is a pretty good summary statement for Behe's and Minnich's claim for the flagellum's irreducible complexity: 'However, it is clear from the details of [the flagellum's] operation that nothing about them works unless every one of their complexly fashioned and integrated components are in place.' And a little further along in the article, he reads, 'In terms of biophysical complexity, the bacterial rotor flagellum is without precedent in the living world. ...To evolutionists the system presents an enigma. To creationists it offers clear and compelling evidence of purposeful intelligent design.' [When asked whether he would agree this was the same argument that he and Behe had advanced for irreducible complexity, Minnich said] "I don't have any problem with that statement.  }}<br>{{cite journal |first=Richard D. |last= Lumsden |title= Not So Blind A Watchmaker |journal= Creation Research Society Quarterly |volume= 31 |issue= 1 |pages= 13–22, quotations from pp. 13, 20 |date= June 1994|url=https://www.public.asu.edu/~jmlynch/origins/documents/lumsden1994.pdf |archive-url=https://web.archive.org/web/20170705125432/http://www.public.asu.edu/%7Ejmlynch/origins/documents/lumsden1994.pdf |archive-date=5 July 2017 |url-status=dead |access-date=27 April 2025|quote=Received 11 May 1993; Revised 15 September 1993}}</ref>

=== Intelligent design ===
The biology supplementary textbook for schools ''[[Of Pandas and People]]'' was drafted presenting [[creation science]] arguments, but shortly after the ''[[Edwards v. Aguillard]]'' ruling, that it was unconstitutional to teach creationism in public school science classes, the authors changed the wording to "intelligent design", introducing the new meaning of this term when the book was published in 1989.{{sfn | Scott | 2009 | pp=122, 149–151}}  In a separate response to the same ruling, law professor [[Phillip E. Johnson]] wrote ''[[Darwin on Trial]]'', published in 1991, and at a conference in March 1992 brought together key figures in what he later called the '[[wedge strategy|wedge movement]]', including biochemistry professor [[Michael Behe]]. According to Johnson, around 1992 Behe developed his ideas of what he later called his "irreducible complexity" concept, and first presented these ideas in June 1993 when the "Johnson-Behe cadre of scholars" met at Pajaro Dunes in California.<ref name=bfwedge>[[Barbara Forrest]], [http://www.talkreason.org/articles/Wedge.cfm#I The Wedge at Work] {{webarchive|url=https://web.archive.org/web/20140905230611/http://www.talkreason.org/articles/Wedge.cfm |date=2014-09-05 }}. Talk Reason.<br />{{cite book |author=Forrest, B |editor=Pennock, RT |chapter=1: The Wedge at Work: How Intelligent Design Creationism is Wedging its way into the Cultural and Academic Mainstream |title=Intelligent design creationism and its critics: philosophical, theological, and scientific perspectives |publisher=MIT Press |location=Cambridge, Mass |year=2001 |pages=[https://archive.org/details/intelligentdesig00robe/page/n26 5]–54 |isbn=978-0-262-66124-9 |url=https://archive.org/details/intelligentdesig00robe |url-access=limited }}</ref>

The second edition of ''Of Pandas and People'', published in 1993, had extensive revisions to Chapter 6 ''Biochemical Similarities'' with new sections on the complex mechanism of blood clotting and on the origin of proteins, written by Behe though he was not initially acknowledged as their author. He argued that "all of the proteins had to be present simultaneously for the blood clotting system to function", so it could not have evolved. In later publications, he named the argument "irreducibly complexity", but changed his definition of this specific system.<ref>[http://ncseweb.org/creationism/analysis/new-pandas-has-creationist-scholarship-improved The New Pandas: Has Creationist Scholarship Improved?] Comments on 1993 Revisions by Frank J. Sonleitner (1994)<br />[http://ncseweb.org/creationism/analysis/critique-pandas-people Introduction: Of Pandas and People, the foundational work of the 'Intelligent Design' movement]{{webarchive|url=https://web.archive.org/web/20081229222228/http://ncseweb.org/creationism/analysis/critique-pandas-people |date=2008-12-29 }} by Nick Matzke 2004.</ref><ref name="flare-up 2006">{{cite web |author= Nick Matzke, NCSE Public Information Director|title=Design on Trial, Just another flare-up|website=National Center for Science Education|quote=Reports of the National Center for Science Education, Volume 26, No. 1-2, January-April 2006  |year= 2006 |url=https://ncse.ngo/design-trial |access-date=26 April 2025}}{{webarchive|url=https://web.archive.org/web/20081229192206/http://ncseweb.org/rncse/26/1-2/design-trial |date=2008-12-29 }} </ref> In ''Doubts About Darwin: A History of Intelligent Design'' (2003), historian Thomas Woodward wrote that "Michael Behe assisted in the rewriting of a chapter on biochemistry in a revised edition of Pandas. The book stands as one of the milestones in the infancy of Design."<ref name="Design on Trial 2004">{{cite web | title=Design on Trial in Dover, Pennsylvania | website= National Center for Science Education | date=14 December 2004 | url=https://ncse.ngo/design-trial-dover-pennsylvania | access-date=28 July 2023}}</ref><ref name="Woodward 2003">{{cite book | last=Woodward | first=T. | title=Doubts about Darwin: A History of Intelligent Design | publisher=Baker Books | year=2003 | isbn=978-0-8010-6443-2 | url=https://books.google.com/books?id=9dkPAQAAIAAJ | access-date=29 July 2023 | page=89}}</ref>

On [[Access Research Network]], Behe posted (on 3 February 1999) "Molecular Machines: Experimental Support for the Design Inference" with a note that "This paper was originally presented in the Summer of 1994 at the meeting of the [[C. S. Lewis]] Society, Cambridge University." An "Irreducible Complexity" section quoted Darwin, then discussed "the humble mousetrap", and "Molecular Machines", going into detail about [[cilium|cilia]] before saying "Other examples of irreducible complexity abound, including aspects of protein transport, blood clotting, closed circular DNA, electron transport, the bacterial flagellum, telomeres, photosynthesis, transcription regulation, and much more. Examples of irreducible complexity can be found on virtually every page of a biochemistry textbook." Suggesting "these things cannot be explained by Darwinian evolution," he said they had been neglected by the scientific community.{{sfn | Forrest | Gross | 2007 | pp=68–69}}<ref name="Behe Molecular Machines">{{cite web | last=Behe | first=Michael J. | title=Molecular Machines: Experimental Support for the Design Inference | website=[[Access Research Network]] | date=3 February 1999 | url=http://arn.org/docs/behe/mb_mm92496.htm | archive-url=https://web.archive.org/web/19990203024838/http://arn.org/docs/behe/mb_mm92496.htm | archive-date=3 February 1999 | url-status=unfit | access-date=28 July 2023|quote=This paper was originally presented in the Summer of 1994 at the meeting of the [[C. S. Lewis]] Society, Cambridge University.}}</ref>

Behe first published the term "irreducible complexity" in his 1996 book ''[[Darwin's Black Box]]'', where he set out his ideas about theoretical properties of some complex biochemical [[cell (biology)|cellular]] systems, now including the bacterial flagellum. He posits that evolutionary mechanisms cannot explain the development of such "irreducibly complex" systems. Notably, Behe credits philosopher [[William Paley]] for the original concept (alone among the predecessors).

Intelligent design advocates argue that irreducibly complex systems must have been deliberately engineered by some form of [[intelligent designer|intelligence]].

In 2001, Behe wrote: "[T]here is an asymmetry between my current definition of irreducible complexity and the task facing natural selection. I hope to repair this defect in future work." Behe specifically explained that the "current definition puts the focus on removing a part from an already functioning system", but the "difficult task facing Darwinian evolution, however, would not be to remove parts from sophisticated pre-existing systems; it would be to bring together components to make a new system in the first place".<ref>{{cite journal |author=Behe, MJ |title=Reply to My Critics: A Response to Reviews of Darwin's Black Box: The Biochemical Challenge to Evolution |journal=Biology and Philosophy |volume=16 |issue=5 |pages=685–709 |date=November 2001 |url=http://friends-of-wisdom.com/readings/Behe2001.pdf |doi=10.1023/A:1012268700496 |s2cid=34945871 |url-status=dead |archive-url=https://web.archive.org/web/20110711040554/http://friends-of-wisdom.com/readings/Behe2001.pdf |archive-date=2011-07-11 }}</ref> In the 2005 ''[[Kitzmiller v. Dover Area School District]]'' trial, Behe testified under oath that he "did not judge [the asymmetry] serious enough to [have revised the book] yet."<ref>[http://www.talkorigins.org/faqs/dover/day12am2.html Behe's testimony in ''Kitzmiller v. Dover''] {{webarchive|url=https://web.archive.org/web/20060629222457/http://www.talkorigins.org/faqs/dover/day12am2.html |date=2006-06-29 }}</ref>

Behe additionally testified that the presence of irreducible complexity in organisms would not rule out the involvement of evolutionary mechanisms in the development of organic life. He further testified that he knew of no earlier "peer reviewed articles in scientific journals discussing the intelligent design of the blood clotting cascade," but that there were "probably a large number of peer reviewed articles in science journals that demonstrate that the blood clotting system is indeed a purposeful arrangement of parts of great complexity and sophistication."<ref>Behe, Michael 2005 [[Wikisource:Kitzmiller v. Dover Area School District/4:Whether ID Is Science#Page 88 of 139|Kitzmiller v. Dover Area School District 4: whether ID is science (p. 88)]]</ref> (The judge ruled that "intelligent design is not science and is essentially religious in nature".)<ref>[[s:Kitzmiller v. Dover Area School District/6:Curriculum, Conclusion#H. Conclusion|Kitzmiller v. Dover Area School District 6: Conclusion, section H]]</ref>

The [[scientific theory]] of [[evolution]] incorporates evidence that genetic variations occur, but makes no assumptions of [[Teleological argument|purposeful design]] or intent. The environment "selects" the variants which have the highest fitness for conditions at the time, and these heritable variations are then passed on to the next generation of organisms. Change occurs by the gradual operation of natural forces over time, perhaps slowly, perhaps more quickly (see [[punctuated equilibrium]]). This process is able to [[adaptation|adapt]] complex structures from simpler beginnings, or convert complex structures from one function to another (see [[spandrel (biology)|spandrel]]). Most intelligent design advocates accept that evolution occurs through mutation and natural selection at the "[[microevolution|micro level]]", such as changing the relative frequency of various beak lengths in finches, but assert that it cannot account for irreducible complexity, because none of the parts of an irreducible system would be functional or advantageous until the entire system is in place.

=== The mousetrap example ===
[[File:Mausefalle 300px.jpg|thumb|200px|[[Michael Behe]] believes that many aspects of life show evidence of design, using the [[mousetrap]] in an analogy disputed by others.<ref name="trap">{{Cite web |last=McDonald |first=John H. |date=2002 |title=A reducibly complex mousetrap |url=https://udel.edu/~mcdonald/mousetrap.html |url-status=live |archive-url=https://web.archive.org/web/20140222041104/http://udel.edu/~mcdonald/mousetrap.html |archive-date=2014-02-22 |access-date=2024-11-14 |website=University of Delaware}}</ref>]]

Behe uses the mousetrap as an illustrative example of this concept. A mousetrap consists of five interacting pieces: the base, the catch, the spring, the hammer, and the hold-down bar. All of these must be in place for the mousetrap to work, as the removal of any one piece destroys the function of the mousetrap. Likewise, he asserts that biological systems require multiple parts working together in order to function. Intelligent design advocates claim that natural selection could not create from scratch those systems for which science is currently unable to find a viable evolutionary pathway of successive, slight modifications, because the selectable function is only present when all parts are assembled.

In his 2008 book ''[[Only A Theory]]'', biologist [[Kenneth R. Miller]] challenges Behe's claim that the mousetrap is irreducibly complex.<ref name=Only /> Miller observes that various subsets of the five components can be devised to form cooperative units, ones that have different functions from the mousetrap and so, in biological terms, could form functional [[spandrel (biology)|spandrels]] before being adapted to the new function of catching mice. In an example taken from his high school experience, Miller recalls that one of his classmates<blockquote>...struck upon the brilliant idea of using an old, broken mousetrap as a spitball catapult, and it worked brilliantly.... It had worked perfectly as something other than a mousetrap.... my rowdy friend had pulled a couple of parts—probably the hold-down bar and catch—off the trap to make it easier to conceal and more effective as a catapult... [leaving] the base, the spring, and the hammer. Not much of a mousetrap, but a helluva spitball launcher.... I realized why [Behe's] mousetrap analogy had bothered me. It was wrong. The mousetrap is not irreducibly complex after all.<ref name=Only>{{cite book |title= Only A Theory |url= https://archive.org/details/onlytheory00kenn |url-access= limited |first= Kenneth R. |last= Miller |location= New York |year= 2008 |publisher= Viking Penguin |pages= [https://archive.org/details/onlytheory00kenn/page/54 54]–55 |isbn= 978-0-670-01883-3}}</ref></blockquote>

Other systems identified by Miller that include mousetrap components include the following:<ref name="Only" />
*use the spitball launcher as a tie clip (same three-part system with different function)
*remove the spring from the spitball launcher/tie clip to create a two-part key chain (base + hammer)
*glue the spitball launcher/tie clip to a sheet of wood to create a clipboard (launcher + glue + wood)
*remove the hold-down bar for use as a toothpick (single element system)

The point of the reduction is that—in biology—most or all of the components were already at hand, by the time it became necessary to build a mousetrap. As such, it required far fewer steps to develop a mousetrap than to design all the components from scratch.

Thus, the development of the mousetrap, said to consist of five different parts which had no function on their own, has been reduced to one step: the assembly from parts that are already present, performing other functions.

=== Consequences ===

Supporters of intelligent design argue that anything less than the complete form of such a system or organ would not work at all, or would in fact be a ''detriment'' to the organism, and would therefore never survive the process of natural selection. Although they accept that some complex systems and organs ''can'' be explained by evolution, they claim that organs and biological features which are ''irreducibly complex'' cannot be explained by current models, and that an intelligent designer must have created life or guided its evolution. Accordingly, the debate on irreducible complexity concerns two questions: whether irreducible complexity can be found in nature, and what significance it would have if it did exist in nature.<ref>{{Cite web|last=Than|first=Ker|title=Why scientists dismiss 'intelligent design'|url=https://www.nbcnews.com/id/wbna9452500|access-date=2021-10-14|website=NBC News|language=en}}</ref>

Behe's original examples of irreducibly complex mechanisms included the bacterial [[flagellum]] of ''[[Escherichia coli|E. coli]]'', [[coagulation|the blood clotting cascade]], [[cilia]], and the [[adaptive immune system]].

Behe argues that organs and biological features which are irreducibly complex cannot be wholly explained by current models of [[evolution]]. In explicating his definition of "irreducible complexity" he notes that:
<blockquote>An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional.</blockquote>

Irreducible complexity is not an argument that evolution does not occur, but rather an argument that it is "incomplete". In the last chapter of ''[[Darwin's Black Box]]'', Behe goes on to explain his view that irreducible complexity is evidence for [[intelligent design]]. Mainstream critics, however, argue that irreducible complexity, as defined by Behe, can be generated by known evolutionary mechanisms. Behe's claim that no scientific literature adequately modeled the origins of biochemical systems through evolutionary mechanisms has been challenged by [[TalkOrigins Archive|TalkOrigins]].<ref>[http://www.talkorigins.org/indexcc/CA/CA350.html Claim CA350: Professional literature is silent on the subject of the evolution of biochemical systems] {{webarchive|url=https://web.archive.org/web/20070304172657/http://www.talkorigins.org/indexcc/CA/CA350.html |date=2007-03-04 }} TalkOrigins Archive.</ref><ref>{{cite book |last= Behe |first= Michael J. |author-link= Michael Behe |title= Darwin's black box: the biochemical challenge to evolution |isbn= 978-0-684-82754-4 |page= 72 |quote= Yet here again the evolutionary literature is totally missing. No scientist has ever published a model to account for the gradual evolution of this extraordinary molecular machine. |year= 1996 |publisher= Free Press |location= New York, NY |orig-year= 1996}}</ref> The judge in the ''Dover'' trial wrote "By defining irreducible complexity in the way that he has, Professor Behe attempts to exclude the phenomenon of [[exaptation]] by definitional fiat, ignoring as he does so abundant evidence which refutes his argument. Notably, the [[United States National Academy of Sciences|NAS]] has rejected Professor Behe's claim for irreducible complexity..."<ref name=kitz74>[[s:Kitzmiller v. Dover Area School District/4:Whether ID Is Science#Page 74 of 139|Ruling]], [[Kitzmiller v. Dover Area School District]], December 2005. Page 74.</ref>