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|caption=Homologous structures. Note how the same basic structure appears repeatedly in different types of forelimbs of different species.}}
;Vestigial structures
Homology includes a unique group of shared structures referred to as ''[[vestigial structures]]''. ''Vestigial'' refers to anatomical parts that are of minimal, if any, value to the organism that possesses them. These apparently illogical structures are remnants of organs that played an important role in ancestral forms. Such is the case in [[whale]]s, which have small vestigial bones that appear to be remnants of the leg bones of [[Evolution of cetaceans|their ancestors]] which walked on land.<ref>{{Harv |Pagel|2002| p=}}</ref> <ref>{{cite web |url= http://www.talkorigins.org/pdf/comdesc.pdf |format= pdf| title=29+ Evidences for Macroevolution Part 2: Past History|accessdate=2008-01-27 |last= Theobald |first= Douglas |coauthors= |date=2004 |work= The Talk.Origins Archive|publisher= The TalkOrigins Foundation }}</ref> Humans also have vestigial structures, including the [[Intrinsic muscles of external ear|ear muscles]], the [[wisdom teeth]], the [[Vermiform appendix|appendix]], the [[tail bone]], [[body hair]] (including [[goose bumps]]), and the [[Plica semilunaris of the conjunctiva|semilunar fold]] in the corner of the [[human eye|eye]].<ref name= johnson>{{citation |last= Johnson|first=George | year =2002 | publication-date = | contribution =Vestigial Structures | contribution-url =http://www.txtwriter.com/backgrounders/Evolution/EVpage12.html| title =The Evidence for Evolution| publisher = 'On Science' column in St. Louis Post Dispatch| url =http://www.txtwriter.com/backgrounders/index.html |format = web resource|accessdate=2008-01-23 }}.</ref>
;Convergent evolution
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