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However, the vermiform appendix of hominoid in particular is often simply called "the appendix"."/> <link rel="alternate" type="application/x-wiki" title="Edit" href="/w/index.php?title=Appendix&action=edit"/> <link rel="edit" title="Edit" href="/w/index.php?title=Appendix&action=edit"/> <link rel="shortcut icon" href="/favicon.ico"/> <link rel="search" type="application/opensearchdescription+xml" href="/w/opensearch_desc.php" title="RationalWiki (en)"/> <link rel="EditURI" type="application/rsd+xml" href="https://rationalwiki.org/w/api.php?action=rsd"/> <link rel="license" href="/wiki/RationalWiki:Copyrights"/> <link rel="alternate" type="application/atom+xml" title="RationalWiki Atom feed" href="/w/index.php?title=Special:RecentChanges&feed=atom"/> <meta property="og:type" content="article"/> <meta property="og:site_name" content="RationalWiki"/> <meta property="og:title" content="Appendix"/> <meta property="og:description" content="An appendix is, anatomically, a section at the end of an organ. 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margin: 0 0 0.5em 0.5em; text-align:left; border: 1px solid #5959DA; width:175px;"> <tbody><tr> <td style="font-size: 95%; text-align:center; color:White; background-color:#5959DA"><b>We're all Homo here</b><br /><a href="/wiki/Evolution" title="Evolution"><font size="5" color="White"><b>Evolution</b></font></a> </td></tr> <tr> <td style="background-color:#E0E0F0;" align="center"><a href="/wiki/Category:Evolution" title="Category:Evolution"><img alt="Icon evolution.svg" src="/w/images/thumb/5/5c/Icon_evolution.svg/100px-Icon_evolution.svg.png" decoding="async" width="100" height="100" srcset="/w/images/thumb/5/5c/Icon_evolution.svg/150px-Icon_evolution.svg.png 1.5x, /w/images/thumb/5/5c/Icon_evolution.svg/200px-Icon_evolution.svg.png 2x" data-file-width="200" data-file-height="200" /></a> </td></tr> <tr> <td style="font-size: 95%; color:White; background-color:#5959DA; text-align:center;"><b>Relevant Hominids</b> </td></tr> <tr> <td style="font-size: 95%; background-color:#E0E0F0;"> <ul><li><a href="/wiki/Charles_Darwin" title="Charles Darwin">Charles Darwin</a></li> <li><a href="/wiki/Alfred_Russel_Wallace" title="Alfred Russel Wallace">Alfred Russel Wallace</a></li> <li><a href="/wiki/Gregor_Mendel" title="Gregor Mendel">Gregor Mendel</a></li> <li><a href="/wiki/Richard_Dawkins" title="Richard Dawkins">Richard Dawkins</a></li> <li><a href="/wiki/Jerry_Coyne" title="Jerry Coyne">Jerry Coyne</a></li></ul> </td></tr> <tr> <td style="font-size: 95%; color:White; background-color:#5959DA; text-align:center;"><b>A Gradual Science</b> </td></tr> <tr> <td style="font-size: 95%; background-color:#E0E0F0;"> <ul><li><a href="/wiki/Human" title="Human">Human</a></li> <li><a href="/wiki/Reptile" title="Reptile">Reptile</a></li> <li><a href="/wiki/Richard_Owen" title="Richard Owen">Richard Owen</a></li> <li><a href="/wiki/Norman_Macbeth" title="Norman Macbeth">Norman Macbeth</a></li></ul> </td></tr> <tr> <td style="font-size: 95%; color:White; background-color:#5959DA; text-align:center;"><b>Plain Monkey Business</b> </td></tr> <tr> <td style="font-size: 95%; background-color:#E0E0F0;"> <ul><li><a href="/wiki/Young_Earth_Creationism" class="mw-redirect" title="Young Earth Creationism">Young Earth Creationism</a></li> <li><a href="/wiki/Old_Earth_Creationism" class="mw-redirect" title="Old Earth Creationism">Old Earth Creationism</a></li> <li><a href="/wiki/Intelligent_Design" class="mw-redirect" title="Intelligent Design">Intelligent Design</a></li> <li><a href="/wiki/Microevolution" class="mw-redirect" title="Microevolution">Microevolution</a> vs. <a href="/wiki/Macroevolution" class="mw-redirect" title="Macroevolution">Macroevolution</a></li></ul> <div class="vte plainlinks" style="font-size:smaller; text-align:center;"><a href="/wiki/Template:Evolution" title="Template:Evolution">v</a> - <a href="/wiki/Template_talk:Evolution" title="Template talk:Evolution">t</a> - <a rel="nofollow" class="external text" href="https://rationalwiki.org/w/index.php?title=Template:Evolution&action=edit">e</a></div> </td></tr></tbody></table> <p>An <b>appendix</b> is, anatomically, a section at the end of an organ. However, the vermiform appendix of <a href="/wiki/Hominid" title="Hominid">hominoid</a> in particular is often simply called "<i>the</i> appendix". </p> <div id="toc" class="toc" role="navigation" aria-labelledby="mw-toc-heading"><input type="checkbox" role="button" id="toctogglecheckbox" class="toctogglecheckbox" style="display:none" /><div class="toctitle" lang="en" dir="ltr"><h2 id="mw-toc-heading">Contents</h2><span class="toctogglespan"><label class="toctogglelabel" for="toctogglecheckbox"></label></span></div> <ul> <li class="toclevel-1 tocsection-1"><a href="#Hominoid_vermiform_appendix"><span class="tocnumber">1</span> <span class="toctext">Hominoid vermiform appendix</span></a> <ul> <li class="toclevel-2 tocsection-2"><a href="#Function"><span class="tocnumber">1.1</span> <span class="toctext">Function</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-3"><a href="#Appendices_in_other_animals"><span class="tocnumber">2</span> <span class="toctext">Appendices in other animals</span></a></li> <li class="toclevel-1 tocsection-4"><a href="#External_links"><span class="tocnumber">3</span> <span class="toctext">External links</span></a></li> <li class="toclevel-1 tocsection-5"><a href="#References"><span class="tocnumber">4</span> <span class="toctext">References</span></a></li> </ul> </div> <h2><span class="mw-headline" id="Hominoid_vermiform_appendix">Hominoid vermiform appendix</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Appendix&action=edit&section=1" title="Edit section: Hominoid vermiform appendix">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>In the digestive system of <a href="/wiki/Humans" class="mw-redirect" title="Humans">humans</a> and other <a href="/wiki/Ape" class="mw-redirect" title="Ape">apes</a>, there exists a <a href="/wiki/Vestigial" class="mw-redirect" title="Vestigial">vestigial</a> extension of the cecum called the vermiform appendix ('vermiform' is <a href="/wiki/Latin" title="Latin">Latin</a> for 'worm-shaped'). It is generally only a few centimetres long, but like many vestiges, the size and orientation is quite variable. Other <a href="/wiki/Primate" title="Primate">primates</a> also have cecal appendices of some sort.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[1]</a></sup> </p><p>The vermiform appendix is particularly vulnerable to inflammation (appendicitis). Appendicitis occurs when the entrance to the appendix becomes blocked, for various reasons, causing the appendix to swell with mucus and, ultimately, burst. As appendicitis is a particularly dangerous condition, due to the risk of peritonitis (infection of the abdominal cavity with gut <a href="/wiki/Bacteria" title="Bacteria">bacteria</a>) leading to sepsis (infection of the entire body), appendicitis may often warrant the removal of the appendix in an appendectomy. </p> <h3><span class="mw-headline" id="Function">Function</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Appendix&action=edit&section=2" title="Edit section: Function">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="thumb tleft"><div class="thumbinner" style="width:202px;"><a href="/wiki/File:Appendix_function_diagram.svg" class="image"><img alt="" src="https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Appendix_function_diagram.svg/200px-Appendix_function_diagram.svg.png" decoding="async" width="200" height="210" class="thumbimage" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Appendix_function_diagram.svg/300px-Appendix_function_diagram.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Appendix_function_diagram.svg/400px-Appendix_function_diagram.svg.png 2x" data-file-width="410" data-file-height="430" /></a> <div class="thumbcaption"><div class="magnify"><a href="/wiki/File:Appendix_function_diagram.svg" class="internal" title="Enlarge"></a></div>A hypothesized function of the human appendix is a safe house for beneficial bacteria in the recovery from diarrhea.</div></div></div> <p>It is sometimes claimed that the appendix plays a role in the immune system, since its walls contain aggregated lymphoid tissue, which are involved in the gut immune system.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2">[2]</a></sup> However, this lymphoid tissue is not confined to the appendix but is found throughout the gut, forming the gut-associated lymphoid tissue. It is therefore not the reason for the appendix: it is clearly not a specialised organ for housing lymphoid tissue, but rather a vestigial part of the colon that keeps its immune function, perhaps just to defend against bacterial infection of the appendix itself. </p><p>In addition, one of the common causes of appendicitis is lymphoid hyperplasia — a growth of the lymphoid tissue around the appendix causing it to become occluded.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3">[3]</a></sup> A part of the immune system which, by its very 'design', frequently leads to infection! The appendix has also been implicated in increasing the risk of Parkinson's disease.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4">[4]</a></sup> </p><p>The purpose of the hominoid appendix still remains something of a physiological mystery; however, several possible answers have been suggested. One <a href="/wiki/Hypothesis" title="Hypothesis">hypothesis</a> states that the human appendix may have once served the same purpose it does in present-day herbivores, such as ruminant mammals — to harbor colonies of bacteria that help in the digestion of cellulose in plant material. Therefore, the hominoid appendix would be a reduced vestige, as the primate diet contains fruit and meat, which contain far richer sources of energy than cellulose.<sup id="cite_ref-held_5-0" class="reference"><a href="#cite_note-held-5">[5]</a></sup><sup class="reference" style="white-space:nowrap;">:127</sup> </p><p>Another hypothesis suggests that the human appendix — as well as the tonsils, the spleen, lymph nodes, and bone marrow — manufacture the antibody-producing white blood cells called <a href="https://en.wikipedia.org/wiki/B_lymphocytes" class="extiw" title="wp:B lymphocytes" rel="nofollow"><span style="color:#477979 !important;" title="Wikipedia: B lymphocytes">B lymphocytes</span></a>.<sup><img alt="" src="https://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/Wikipedia%27s_W.svg/12px-Wikipedia%27s_W.svg.png" decoding="async" width="12" height="12" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/Wikipedia%27s_W.svg/18px-Wikipedia%27s_W.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/Wikipedia%27s_W.svg/24px-Wikipedia%27s_W.svg.png 2x" data-file-width="128" data-file-height="128" /></sup><sup id="cite_ref-held_5-1" class="reference"><a href="#cite_note-held-5">[5]</a></sup><sup class="reference" style="white-space:nowrap;">:127</sup> </p><p>A third hypothesis is that the appendix may "attract" infections within the body. In that way, infections become localized in one organ that is not critical to body function. If this was shown to be the case, then it could be argued that the appendix is a derived organ rather than a vestige. </p><p>Regardless of what the function may be, there is no evidence that a person with a removed or congenitally absent appendix has any noticeable consequences due their lack of the structure. Therefore, any function it may have is clearly very minor indeed.<sup id="cite_ref-held_5-2" class="reference"><a href="#cite_note-held-5">[5]</a></sup><sup class="reference" style="white-space:nowrap;">:127-128</sup> </p><p>Information published in 2007 indicates that the appendix is essentially a safe-house for normal flora (i.e. good bacteria) during episodes of diarrhea, a function more useful in developing countries or in historical times.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6">[6]</a></sup> </p> <h2><span class="mw-headline" id="Appendices_in_other_animals">Appendices in other animals</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Appendix&action=edit&section=3" title="Edit section: Appendices in other animals">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>Some other animals, such as the wombat, oppossum and the rabbit (and some rodents) have a vermiform appendix also, however phylogenic analyses have shown that these are not homologous to the appendix of apes.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7">[7]</a></sup> That is, they were developed multiple times — examples of <a href="/wiki/Convergent_evolution" class="mw-redirect" title="Convergent evolution">convergent evolution</a>.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8">[8]</a></sup> </p> <h2><span class="mw-headline" id="External_links">External links</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Appendix&action=edit&section=4" title="Edit section: External links">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <ul><li><a rel="nofollow" class="external text" href="http://www.talkorigins.org/faqs/vestiges/appendix.html">The Vestigiality of the Human Vermiform Appendix</a> by Doug Theobald of <a href="/wiki/Talk.origins" title="Talk.origins">talk.origins</a></li></ul> <h2><span class="mw-headline" id="References">References</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Appendix&action=edit&section=5" title="Edit section: References">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <div class="references-small" style="-moz-column-count:2; -webkit-column-count:2; column-count:2; font-size:80%;"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text">Fisher, Rebecca. 2000. "The Primate Appendix: A Reassessment" <i>Anat. Rec.</i> <b>261</b>(6):228-236, 18 Dec 2000. [<a rel="nofollow" class="external text" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11135184">PubMed</a>]</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text">Bergman, Jerry. 2000. <a rel="nofollow" class="external text" href="http://www.answersingenesis.org/tj/v14/i2/vestigial.asp">Do any vestigial organs exist in humans?</a> <i>Technical Journal</i> <b>14</b>(2):95-98, August 2000</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><a href="#cite_ref-3">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.ajronline.org/doi/10.2214/AJR.15.14846Lymphoid">Hyperplasia of the Appendix: A Potential Pitfall in the Sonographic Diagnosis of Appendicitis</a> by Yingding Xu et al. (2016) <i>American Journal of Roentgenology</i> 206:189-194.</span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><a href="#cite_ref-4">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.sciencenews.org/article/appendix-implicated-parkinsons-disease">The appendix is implicated in Parkinson’s disease: Having an appendectomy lowered the risk of developing the neurodegenerative disease</a> by Aimee Cunningham (2:00pm, October 31, 2018) <i>Science News</i>.</span> </li> <li id="cite_note-held-5"><span class="mw-cite-backlink">↑ <sup><a href="#cite_ref-held_5-0">5.0</a></sup> <sup><a href="#cite_ref-held_5-1">5.1</a></sup> <sup><a href="#cite_ref-held_5-2">5.2</a></sup></span> <span class="reference-text"><i>Quirks of Human Anatomy: An Evo-Devo Look at the Human Body</i> by Lewis I. Held, Jr. (2009) Cambridge University Press. ISBN 0521732336.</span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><a href="#cite_ref-6">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.sciencedaily.com/releases/2007/10/071008102334.htm">Appendix Isn't Useless At All: It's A Safe House For Good Bacteria</a> October 8, 2007 <i>ScienceDaily</i>.</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><a href="#cite_ref-7">↑</a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r2708880">/* Errors processing stylesheet [[:Module:Citation/CS1/styles.css]] (rev 2708880): • Invalid or unsupported value for property ⧼code⧽background⧼/code⧽ at line 44 character 14. • Invalid or unsupported value for property ⧼code⧽background⧼/code⧽ at line 50 character 14. • Invalid or unsupported value for property ⧼code⧽background⧼/code⧽ at line 55 character 14. • Invalid or unsupported value for property ⧼code⧽background⧼/code⧽ at line 64 character 14. • Invalid or unsupported value for property ⧼code⧽color⧼/code⧽ at line 96 character 9. • Invalid or unsupported value for property ⧼code⧽color⧼/code⧽ at line 100 character 9. • Invalid media query at line 138 character 8. */ .mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{}.mw-parser-output .id-lock-subscription.id-lock-subscription a{}.mw-parser-output .cs1-ws-icon a{}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none}.mw-parser-output .cs1-visible-error{}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation journal cs1">"<span class="cs1-kern-left"></span>"Higher Taxonomic Relationships among Extant Mammals Based on Morphology, with Selected Comparisons of Results from Molecular Data"<span class="cs1-kern-right"></span>". <i>Mol. Phylogenet. Evol.</i>: 572-584. June 1998.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Mol.+Phylogenet.+Evol.&rft.atitle=%22Higher+Taxonomic+Relationships+among+Extant+Mammals+Based+on+Morphology%2C+with+Selected+Comparisons+of+Results+from+Molecular+Data%22&rft.pages=572-584&rft.date=1998-06&rfr_id=info%3Asid%2Frationalwiki.org%3AAppendix" class="Z3988"></span> <span class="cs1-visible-error citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_journal" title="Template:Cite journal">cite journal</a>}}</code>: </span><span class="cs1-visible-error citation-comment">Unknown parameter <code class="cs1-code">|authors=</code> ignored (<a href="/wiki/Help:CS1_errors#parameter_ignored" title="Help:CS1 errors">help</a>)</span>; <span class="cs1-visible-error citation-comment">Unknown parameter <code class="cs1-code">|part=</code> ignored (<a href="/wiki/Help:CS1_errors#parameter_ignored" title="Help:CS1 errors">help</a>)</span>; <span class="cs1-visible-error citation-comment">Unknown parameter <code class="cs1-code">|vol=</code> ignored (<code class="cs1-code">|volume=</code> suggested) (<a href="/wiki/Help:CS1_errors#parameter_ignored_suggest" title="Help:CS1 errors">help</a>)</span><span class="cs1-maint citation-comment">CS1 maint: date and year (<a href="/wiki/Category:CS1_maint:_date_and_year" title="Category:CS1 maint: date and year">link</a>)</span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><a href="#cite_ref-8">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://onlinelibrary.wiley.com/doi/10.1002/ar.21357/abstract;jsessionid=679A25FA39A9D1EEFB175AC4F3B0DFEF.f04t02">The Cecal Appendix: One More Immune Component With a Function Disturbed By Post-Industrial Culture</a> by Michel Laurin et al. 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