Editing Irreducible complexity (section)

== Claimed examples ==
Behe and others have suggested a number of biological features that they believed to be irreducibly complex.

=== Blood clotting cascade ===
The process of blood clotting or [[coagulation]] cascade in vertebrates is a complex biological pathway which is given as an example of apparent irreducible complexity.<ref>Action, George [http://www.talkorigins.org/origins/postmonth/feb97.html "Behe and the Blood Clotting Cascade"] {{webarchive|url=https://web.archive.org/web/20050605075004/http://www.talkorigins.org/origins/postmonth/feb97.html |date=2005-06-05 }}</ref>

The irreducible complexity argument assumes that the necessary parts of a system have always been necessary, and therefore could not have been added sequentially. However, in evolution, something which is at first merely advantageous can later become necessary.<ref name="incoherence">{{cite journal |last1=Boudry |first1=Maarten |author-link=Maarten Boudry |last2=Blancke |first2=Stefaan |last3=Braeckman |first3=Johan |author-link3=Johan Braeckman |title=Irreducible Incoherence and Intelligent Design: A Look into the Conceptual Toolbox of a Pseudoscience |journal=[[Quarterly Review of Biology]] |volume=85 |issue=3 |pages=473–82 |date=September 2010 |url=http://sites.google.com/site/maartenboudry/irreducible-incoherence |doi=10.1086/656904 |pmid=21243965 |url-status=live |archive-url=https://web.archive.org/web/20101130095300/http://sites.google.com/site/maartenboudry/irreducible-incoherence |archive-date=2010-11-30 |hdl=1854/LU-952482 |s2cid=27218269 |hdl-access=free }}</ref> [[Natural selection]] can lead to complex biochemical systems being built up from simpler systems, or to existing functional systems being recombined as a new system with a different function.<ref name="kitz74" /> For example, one of the clotting factors that Behe listed as a part of the clotting cascade ([[Factor XII]], also called Hageman factor) was later found to be absent in whales, demonstrating that it is not essential for a clotting system.<ref>{{cite journal |vauthors=Semba U, Shibuya Y, Okabe H, Yamamoto T |title=Whale Hageman factor (factor XII): prevented production due to pseudogene conversion |journal=Thromb Res |year=1998 |pages=31–7 |volume=90 |issue=1 |pmid=9678675 |doi= 10.1016/S0049-3848(97)00307-1}}</ref> Many purportedly irreducible structures can be found in other organisms as much simpler systems that utilize fewer parts. These systems, in turn, may have had even simpler precursors that are now extinct. Behe has responded to critics of his clotting cascade arguments by suggesting that [[homology (biology)|homology]] is evidence for evolution, but not for natural selection.<ref>Behe, Michael [http://www.arn.org/docs/behe/mb_indefenseofbloodclottingcascade.htm "In Defense of the Irreducibility of the Blood Clotting Cascade: Response to Russell Doolittle, Ken Miller and Keith Robison"] {{webarchive|url=https://web.archive.org/web/20100917181325/http://arn.org/docs/behe/mb_indefenseofbloodclottingcascade.htm |date=2010-09-17 }}</ref>

The "improbability argument" also misrepresents natural selection. It is correct to say that a set of simultaneous mutations that form a complex protein structure is so unlikely as to be unfeasible, but that is not what Darwin advocated. His explanation is based on small accumulated changes that take place without a final goal. Each step must be advantageous in its own right, although biologists may not yet understand the reason behind all of them—for example, [[jawless fish]] accomplish blood clotting with just six proteins instead of the full ten.<ref>[https://www.newscientist.com/article/mg18725073.800 Creationism special: A sceptic's guide to intelligent design] {{webarchive|url=https://web.archive.org/web/20150506100626/http://www.newscientist.com/article/mg18725073.800 |date=2015-05-06 }}, New Scientist, 9 July 2005</ref>

=== Eye ===
{{Main|Evolution of the eye}}
[[File:Stages in the evolution of the eye.png|thumb|300px|Stages in the evolution of the eye<br />(a) A pigment spot<br />(b) A simple pigment cup<br />(c) The simple optic cup found in [[abalone]]<br />(d) The complex lensed eye of the marine snail and the octopus]]
The [[eye]] is frequently cited by intelligent design and creationism advocates as a purported example of irreducible complexity. Behe used the "development of the eye problem" as evidence for intelligent design in ''Darwin's Black Box''. Although Behe acknowledged that the evolution of the larger anatomical features of the eye have been well-explained, he pointed out that the complexity of the minute biochemical reactions required at a molecular level for light sensitivity still defies explanation. Creationist [[Jonathan Sarfati]] has described the eye as evolutionary biologists' "greatest challenge as an example of superb 'irreducible complexity' in God's creation", specifically pointing to the supposed "vast complexity" required for transparency.<ref name="aig">[[Jonathan Sarfati|Sarfati, Jonathan]] (2000). [http://www.answersingenesis.org/home/area/re2/chapter10.asp Argument: 'Irreducible complexity'] {{webarchive|url=https://web.archive.org/web/20051123070148/http://www.answersingenesis.org/home/area/re2/chapter10.asp|date=2005-11-23}}, from ''[[Refuting Evolution]]'' ([[Answers in Genesis]]).</ref>{{failed verification|redirects to http://www.answersingenesis.org/get-answers/topic/design-features, an unauthored blog|date=June 2012}}{{primary source inline|date=September 2020}}

In an often misquoted<ref>{{cite web|url=http://www.talkorigins.org/indexcc/CA/CA113_1.html|title=CA113.1: Evolution of the eye.|first=Mark|last=Isaak|website=www.talkorigins.org|access-date=7 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171003062117/http://www.talkorigins.org/indexcc/CA/CA113_1.html|archive-date=3 October 2017}}</ref> passage from ''[[On the Origin of Species]]'', [[Charles Darwin]] appears to acknowledge the eye's development as a difficulty for his theory. However, the quote in context shows that Darwin actually had a very good understanding of the evolution of the eye (see [[fallacy of quoting out of context]]). He notes that "to suppose that the eye ... could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree". Yet this observation was merely a [[procatalepsis|rhetorical device]] for Darwin. He goes on to explain that if gradual evolution of the eye could be shown to be possible, "the difficulty of believing that a perfect and complex eye could be formed by natural selection ... can hardly be considered real". He then proceeded to roughly map out a likely course for evolution using examples of gradually more complex eyes of various species.<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=204 pages 186ff, Chapter VI] {{webarchive|url=https://web.archive.org/web/20070927190830/http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=204 |date=2007-09-27 }}</ref>

[[File:Evolution eye.svg|thumb|left|200px|The eyes of vertebrates (left) and invertebrates such as the [[octopus]] (right) developed independently: vertebrates evolved an inverted [[retina]] with a [[blind spot (vision)|blind spot]] over their [[optic disc]], whereas octopuses avoided this with a non-inverted retina. (1 photo-receptors, 2 neural tissue, 3 optic nerve, 4 blind spot)]]

Since Darwin's day, the eye's ancestry has become much better understood. Although learning about the construction of ancient eyes through fossil evidence is problematic due to the soft tissues leaving no imprint or remains, genetic and comparative anatomical evidence has increasingly supported the idea of a common ancestry for all eyes.<ref>{{cite journal |vauthors=Halder G, Callaerts P, Gehring WJ |title=New perspectives on eye evolution |journal=Current Opinion in Genetics & Development |volume=5 |issue=5 |pages=602–9 |date=October 1995 |pmid=8664548 |doi=10.1016/0959-437X(95)80029-8 }}</ref><ref>{{cite journal |vauthors=Halder G, Callaerts P, Gehring WJ |title=Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila |journal=Science |volume=267 |issue=5205 |pages=1788–92 |date=March 1995 |pmid=7892602 |doi=10.1126/science.7892602 |bibcode=1995Sci...267.1788H|s2cid=9646449 }}</ref><ref>{{cite journal |vauthors=Tomarev SI, Callaerts P, Kos L, etal |title=Squid Pax-6 and eye development |journal=Proc Natl Acad Sci USA |volume=94 |issue=6 |pages=2421–6 |date=March 1997 |pmid=9122210 |pmc=20103 |doi=10.1073/pnas.94.6.2421 |bibcode=1997PNAS...94.2421T|doi-access=free }}</ref>

Current evidence does suggest possible evolutionary lineages for the origins of the anatomical features of the eye. One likely chain of development is that the eyes originated as simple patches of [[photoreceptor cell]]s that could detect the presence or absence of light, but not its direction. When, via random mutation across the population, the photosensitive cells happened to have developed on a small depression, it endowed the organism with a better sense of the light's source. This small change gave the organism an advantage over those without the mutation. This genetic trait would then be "selected for" as those with the trait would have an increased chance of survival, and therefore progeny, over those without the trait. Individuals with deeper depressions would be able to discern changes in light over a wider field than those individuals with shallower depressions. As ever deeper depressions were advantageous to the organism, gradually, this depression would become a pit into which light would strike certain cells depending on its angle. The organism slowly gained increasingly precise visual information. And again, this gradual process continued as individuals having a slightly shrunken [[aperture]] of the eye had an advantage over those without the mutation as an aperture increases how [[collimated]] the light is at any one specific group of photoreceptors. As this trait developed, the eye became effectively a [[pinhole camera]] which allowed the organism to dimly make out shapes—the [[nautilus]] is a modern example of an animal with such an eye. Finally, via this same selection process, a protective layer of transparent cells over the aperture was differentiated into a crude [[lens (anatomy)|lens]], and the interior of the eye was filled with humours to assist in focusing images.<ref>Fernald, Russell D. (2001). [http://www.karger.com/gazette/64/fernald/art_1_1.htm The Evolution of Eyes: Why Do We See What We See?] {{webarchive|url=https://web.archive.org/web/20060319045945/http://www.karger.com/gazette/64/fernald/art_1_1.htm |date=2006-03-19 }} ''Karger Gazette'' 64: "The Eye in Focus".</ref><ref>{{cite book |author=Fernald, RD |chapter=Aquatic Adaptations in Fish Eyes |editor=Atema, J |title=Sensory biology of aquatic animals |publisher=Springer-Verlag |location=Berlin |year=1988 |isbn=978-0-387-96373-0}}</ref><ref>{{cite journal |author=Fernald, RD |title=The evolution of eyes |journal=Brain Behav. Evol. |volume=50 |issue=4 |pages=253–9 |year=1997 |pmid=9310200 |doi=10.1159/000113339|s2cid=46796856 }}</ref> In this way, eyes are recognized by modern biologists as actually a relatively unambiguous and simple structure to evolve, and many of the major developments of the eye's evolution are believed to have taken place over only a few million years, during the [[Cambrian explosion]].<ref>{{cite book |author=Conway-Morris, S |title=The Crucible of Creation: The Burgess Shale and the Rise of Animals |publisher=Oxford University Press |location=Oxford [Oxfordshire] |year=1999 |isbn=978-0-19-286202-0 |url=https://archive.org/details/crucibleofcreati00conw }}</ref> Behe asserts that this is only an explanation of the gross anatomical steps, however, and not an explanation of the changes in discrete biochemical systems that would have needed to take place.<ref>{{Cite book|title=Darwin's Black Box|last=Behe|first=Michael|publisher=Free Press|year=2006|isbn=978-0-7432-9031-9|pages=38}}</ref>

Behe maintains that the complexity of light sensitivity at the molecular level and the minute biochemical reactions required for those first "simple patches of photoreceptor[s]" still defies explanation, and that the proposed series of infinitesimal steps to get from patches of photoreceptors to a fully functional eye would actually be considered great, complex leaps in evolution if viewed on the molecular scale. Other intelligent design proponents claim that the evolution of the entire visual system would be difficult rather than the eye alone.<ref>{{cite book|title=A Meaningful World|url=https://archive.org/details/meaningfulworldh00wike|url-access=limited|year=2006|first1=Benjamin |last1=Wiker |first2=Jonathan |last2=Witt |page=[https://archive.org/details/meaningfulworldh00wike/page/n41 44]|publisher=InterVarsity Press |isbn=978-0-8308-2799-2}}</ref>

=== Flagella ===
{{Main|Evolution of flagella}}

The [[flagella]] of certain bacteria constitute a [[molecular motor]] requiring the interaction of about 40 different protein parts. The flagellum (or cilium) developed from the pre-existing components of the eukaryotic cytoskeleton.<ref>{{Citation |last=Mitchell |first=David R. |title=The Evolution of Eukaryotic Cilia and Flagella as Motile and Sensory Organelles |date=2007 |url=https://doi.org/10.1007/978-0-387-74021-8_11 |work=Eukaryotic Membranes and Cytoskeleton: Origins and Evolution |pages=130–140 |access-date=2023-06-25 |series=Advances in Experimental Medicine and Biology |volume=607 |place=New York, NY |publisher=Springer |language=en |doi=10.1007/978-0-387-74021-8_11 |isbn=978-0-387-74021-8 |pmc=3322410 |pmid=17977465}}</ref><ref>{{Cite journal |last1=Wickstead |first1=Bill |last2=Gull |first2=Keith |date=2011-08-22 |title=The evolution of the cytoskeleton |url=https://doi.org/10.1083/jcb.201102065 |journal=Journal of Cell Biology |volume=194 |issue=4 |pages=513–525 |doi=10.1083/jcb.201102065 |issn=1540-8140 |pmc=3160578 |pmid=21859859}}</ref> In bacterial flagella, strong evidence points to an evolutionary pathway from a Type III secretory system, a simpler bacterial secretion system.<ref>{{Cite journal |last1=Milne-Davies |first1=Bailey |last2=Wimmi |first2=Stephan |last3=Diepold |first3=Andreas |date=March 2021 |title=Adaptivity and dynamics in type III secretion systems |journal=Molecular Microbiology |language=en |volume=115 |issue=3 |pages=395–411 |doi=10.1111/mmi.14658 |pmid=33251695 |issn=0950-382X|doi-access=free }}</ref> Despite this, Behe presents this as a prime example of an irreducibly complex structure defined as "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", and argues that since "an irreducibly complex system that is missing a part is by definition nonfunctional", it could not have evolved gradually through [[natural selection]].<ref name="Flagellum Unspun" /> However, each of the three types of flagella—eukaryotic, bacterial, and archaeal—has been shown to have evolutionary pathways. For archaeal flagella, there is a molecular homology with bacterial Type IV pili, pointing to an evolutionary link.<ref>{{Cite journal |last1=Faguy |first1=David M. |last2=Jarrell |first2=Ken F. |last3=Kuzio |first3=John |last4=Kalmokoff |first4=Martin L. |date=1994-01-01 |title=Molecular analysis of archaeal flagellins: similarity to the type IV pilin – transport superfamily widespread in bacteria |url=http://www.nrcresearchpress.com/doi/10.1139/m94-011 |journal=Canadian Journal of Microbiology |language=en |volume=40 |issue=1 |pages=67–71 |doi=10.1139/m94-011 |pmid=7908603 |issn=0008-4166|url-access=subscription }}</ref> In all these cases, intermediary, simpler forms of the structures are possible and provide partial functionality.

'''Reducible complexity'''. In contrast to Behe's claims, many proteins can be deleted or mutated and the flagellum still works, even though sometimes at reduced efficiency.<ref>{{cite journal |vauthors=Rajagopala SV, Titz B, Goll J, Parrish JR, Wohlbold K, McKevitt MT, Palzkill T, Mori H, ((Finley RL Jr)), Uetz P |year= 2007 |title= The protein network of bacterial motility |journal= Mol Syst Biol |volume= 3 |page= 128 |doi= 10.1038/msb4100166 |pmid= 17667950 |pmc=1943423}}</ref> In fact, the composition of flagella is surprisingly diverse across bacteria with many proteins only found in some species but not others.<ref>{{cite journal |vauthors=Titz B, Rajagopala SV, Ester C, Häuser R, Uetz P |date= Nov 2006 |title= Novel conserved assembly factor of the bacterial flagellum |journal= J Bacteriol |volume= 188 |issue= 21 |pages= 7700–6 |doi= 10.1128/JB.00820-06 |pmid= 16936039 |pmc=1636259}}</ref> Hence the flagellar apparatus is clearly very flexible in evolutionary terms and perfectly able to lose or gain protein components. Further studies have shown that, contrary to claims of "irreducible complexity", flagella and the [[Type three secretion system|type-III secretion system]] share several components which provides strong evidence of a shared evolutionary history (see below). In fact, this example shows how a complex system can evolve from simpler components.<ref>{{cite journal |last1= Pallen |first1= M. J. |last2= Gophna |first2= U. |doi= 10.1159/000107602 |title= Bacterial Flagella and Type III Secretion: Case Studies in the Evolution of Complexity |journal= Gene and Protein Evolution |series= Genome Dynamics |volume= 3 |pages= 30–47 |year= 2007 |isbn= 978-3-8055-8340-4 |pmid= 18753783}}</ref><ref>{{cite journal |last1= Clements |first1= A. |last2= Bursac |first2= D. |last3= Gatsos |first3= X. |last4= Perry |first4= A. |last5= Civciristov |first5= S. |last6= Celik |first6= N. |last7= Likic |first7= V. |last8= Poggio |first8= S. |last9= Jacobs-Wagner |first9= C. |last10= Strugnell |first10= R. A. |last11= Lithgow |first11= T. |title= The reducible complexity of a mitochondrial molecular machine |journal= Proceedings of the National Academy of Sciences of the United States of America |volume= 106 |issue= 37 |pages= 15791–15795 |year= 2009 |pmid= 19717453 |pmc= 2747197 |doi= 10.1073/pnas.0908264106|bibcode= 2009PNAS..10615791C|doi-access= free }}</ref> Multiple processes were involved in the evolution of the flagellum, including [[horizontal gene transfer]].<ref>{{cite journal|last1=Zuckerkandl|first1=Emile|title=Intelligent design and biological complexity|journal=Gene|date=December 2006|volume=385|pages=2–18|doi=10.1016/j.gene.2006.03.025|pmid=17011142}}</ref>

'''Evolution from type three secretion systems'''. The basal body of the flagella has been found to be similar to the [[Type three secretion system|Type III secretion system]] (TTSS), a needle-like structure that pathogenic germs such as ''[[Salmonella]]'' and ''[[Yersinia pestis]]'' use to inject [[toxin]]s into living [[eukaryote]] cells.<ref name="Flagellum Unspun">Miller, Kenneth R. [http://www.millerandlevine.com/km/evol/design2/article.html The Flagellum Unspun: The Collapse of "Irreducible Complexity"] {{webarchive|url=https://web.archive.org/web/20140214024810/http://www.millerandlevine.com/km/evol/design2/article.html |date=2014-02-14 }} with reply here {{cite web |url=http://www.designinference.com/documents/2003.02.Miller_Response.htm |title=The Bacterial Flagellum: Still Spinning Just Fine |access-date=2006-04-26 |url-status=dead |archive-url=https://web.archive.org/web/20060403013818/http://designinference.com/documents/2003.02.Miller_Response.htm |archive-date=2006-04-03 }}</ref><ref>{{cite journal |last1=Pallen |first1=M.J. |last2=Matzke |first2=N.J. |year=2006 |title=From ''The Origin of Species'' to the origin of bacterial flagella |journal=Nature Reviews Microbiology |volume=4 |issue= 10|pages=784–790 |doi=10.1038/nrmicro1493 |pmid=16953248|s2cid=24057949 }}</ref> The needle's base has ten elements in common with the flagellum, but it is missing forty of the proteins that make a flagellum work.<ref>[https://www.youtube.com/watch?v=RQQ7ubVIqo4 Kenneth Miller's The Collapse of Intelligent Design: Section 5 Bacterial Flagellum] {{webarchive|url=https://web.archive.org/web/20161017080729/https://www.youtube.com/watch?v=RQQ7ubVIqo4 |date=2016-10-17 }} (Case Western Reserve University, 2006 January 3)</ref> The TTSS system negates Behe's claim that taking away any one of the flagellum's parts would prevent the system from functioning. On this basis, [[Kenneth R. Miller|Kenneth Miller]] notes that, "The parts of this supposedly irreducibly complex system actually have functions of their own."<ref>[https://web.archive.org/web/20071010035647/http://debatebothsides.com/showthread.php?t=38338 Unlocking cell secrets bolsters evolutionists] (Chicago Tribune, 2006 February 13)</ref><ref>[http://www.talkdesign.org/faqs/flagellum.html Evolution in (Brownian) space: a model for the origin of the bacterial flagellum] {{webarchive|url=https://web.archive.org/web/20160919205453/http://www.talkdesign.org/faqs/flagellum.html |date=2016-09-19 }} (Talk Design, 2006 September)</ref> Studies have also shown that similar parts of the flagellum in different bacterial species can have different functions despite showing evidence of common descent, and that certain parts of the flagellum can be removed without eliminating its functionality.<ref>{{cite book |last1=Maloy |first1=Stanley |title=Brenner's Encyclopedia of Genetics (Second Edition)|date=1 January 2013 |pages=112–114   |publisher=Academic Press |doi=10.1016/B978-0-12-374984-0.00806-8|isbn=978-0-08-096156-9 }}</ref> Behe responded to Miller by asking "why doesn't he just take an appropriate bacterial species, knock out the genes for its flagellum, place the bacterium under selective pressure (for mobility, say), and experimentally produce a flagellum—or any equally complex system—in the laboratory?"<ref>{{Cite web |last=Michael |first=Behe |author-link=Michael Behe |date=2016-10-27 |title=Philosophical Objections to Intelligent Design: A Response to Critics |url=https://evolutionnews.org/2016/10/philosophical_o/ |access-date=2022-10-12 |website=Evolution News |language=en-US}}</ref> However a laboratory experiment has been performed where "immotile strains of the bacterium Pseudomonas fluorescens that lack flagella [...] regained flagella within 96 hours via a two-step evolutionary pathway", concluding that "natural selection can rapidly rewire regulatory networks in very few, repeatable mutational steps".<ref name=":0">{{Cite journal |last1=Taylor |first1=Tiffany B. |last2=Mulley |first2=Geraldine |last3=Dills |first3=Alexander H. |last4=Alsohim |first4=Abdullah S. |last5=McGuffin |first5=Liam J. |last6=Studholme |first6=David J. |last7=Silby |first7=Mark W. |last8=Brockhurst |first8=Michael A. |last9=Johnson |first9=Louise J. |last10=Jackson |first10=Robert W. |date=2015-02-27 |title=Evolution. Evolutionary resurrection of flagellar motility via rewiring of the nitrogen regulation system |url=https://pubmed.ncbi.nlm.nih.gov/25722415/ |journal=Science |volume=347 |issue=6225 |pages=1014–1017 |doi=10.1126/science.1259145 |issn=1095-9203 |pmid=25722415|s2cid=206561157 |hdl=10871/16523 |hdl-access=free }}</ref>

Dembski has argued that phylogenetically, the TTSS is found in a narrow range of bacteria which makes it seem to him to be a late innovation, whereas flagella are widespread throughout many bacterial groups, and he argues that it was an early innovation.<ref>{{cite web|url=http://www.evolutionnews.org/2010/01/spinning_tales_about_the_bacte031141.html|title=Spinning Tales About the Bacterial Flagellum – Evolution News|date=21 January 2010|website=evolutionnews.org|access-date=7 May 2018|url-status=live|archive-url=https://web.archive.org/web/20160304053315/http://www.evolutionnews.org/2010/01/spinning_tales_about_the_bacte031141.html|archive-date=4 March 2016}}</ref><ref>Dembski, [https://web.archive.org/web/20051026133901/http://www.designinference.com/documents/2005.09.Expert_Rebuttal_Dembski.pdf Rebuttal to Reports by Opposing Expert Witnesses, p. 52]</ref> Against Dembski's argument, different flagella use completely different mechanisms, and publications show a plausible path in which bacterial flagella could have evolved from a secretion system.<ref name="CB200.1:">{{cite web |last= Isaak |first= Mark |title= CB200.1: Bacterial flagella and Irreducibly Complexity |url= http://www.talkorigins.org/indexcc/CB/CB200_1.html |publisher= TalkOrigins Archive |year= 2006 |access-date= 25 June 2013 |url-status= live |archive-url= https://web.archive.org/web/20130704075446/http://www.talkorigins.org/indexcc/CB/CB200_1.html |archive-date= 4 July 2013 }}</ref>

=== Cilium motion ===

The [[cilium]] construction of [[axoneme]] microtubules movement by the sliding of [[dynein]] protein was cited by Behe as an example of irreducible complexity.<ref>page 90: "Just as a mousetrap does not work unless all of its constituent parts are present, ciliary motion simply does not exist in the absence of microtubules, connectors, and motors.  Therefore we can conclude that the cilium is irreducibly complex – an enormous monkey wrench thrown into its presumed gradual, Darwinian evolution."{{cite book| title = Signs of Intelligence, article Darwin's Breakdown: Irreducible Complexity and Design at the Foundation of Life| author = Behe, Michael| year = 1999| publisher = Brazos Press| isbn = 978-1-58743-004-6| author-link = Michael Behe| url-access = registration| url = https://archive.org/details/signsofintellige0000unse}}</ref>  He further said that the advances in knowledge in the subsequent 10 years had shown that the complexity of [[intraflagellar transport]] for two hundred components cilium and many other cellular structures is substantially greater than was known earlier.<ref>pg 95 {{cite book| title = The Edge of Evolution | url = https://archive.org/details/isbn_9780743296205 | url-access = registration | author = Behe, Michael| year = 2007| publisher = FreePress division of Simon & Schuster| isbn = 978-0-7432-9622-9| author-link = Michael Behe}}</ref>