Editing Irreducible complexity (section)

=== 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>