Homology

[[File:Limb homology.png|thumb|right|300px|Forelimb homology among vertebrates, with colors indicating homologous parts: A=[[human]], B=[[dog]], C=[[bird]], D=whale]]
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'''Homology''', also known as '''comparative anatomy''', in biology is the occurrence and study of shared traits between different taxa due to [[common descent]]. The term ''homology'' was coined by the infamous [[British]] [[paleontologist]] and anatomist [[Richard Owen]] in 1845, and was later explained as a result of [[Darwin]]'s [[theory]] of [[evolution]] after the publication of the ''Origin'' in 1859.<ref>{{cite book |author=Owen, Richard |title=Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, Delivered at the Royal College of Surgeons in 1843 |publisher=Longman, Brown, Green, and Longmans |date=1843 |url=https://www.biodiversitylibrary.org/item/29826#page/5/mode/1up |pages=374, 379}}</ref><ref>{{cite journal |last1=Sommer |first1=R. J. |title=Homology and the hierarchy of biological systems |journal=BioEssays |date=July 2008 |volume=30 |issue=7 |pages=653–658 |pmid=18536034}}</ref>

==Definition==
Homology, as stated above, refers to the occurrence of shared traits or structures in different but related taxa that is a result of shared ancestry. Homology therefore implies divergent evolution from a common ancestor, for example, many [[insects]] share two sets of wings, this shared feature among insects is a result of common ancestry, and therefore is considered to be a ''homologous structure''.<ref>{{cite book |last=Wagner |first=Günter P. |title=Homology, Genes, and Evolutionary Innovation |url=https://books.google.com/books?id=g7vzAgAAQBAJ&pg=PA53 |year=2014 |publisher=Princeton University Press |isbn=978-1-4008-5146-1 |pages=53–54 |quote=elytra have very little similarity with typical wings, but are clearly homologous to forewings. Hence butterflies, flies, and beetles all have two pairs of dorsal appendages that are homologous among species.}}</ref><ref>{{cite book |last=Lipshitz |first=Howard D. |title=Genes, Development and Cancer: The Life and Work of Edward B. Lewis |url=https://books.google.com/books?id=8g4GCAAAQBAJ&pg=PA240 |year=2012 |publisher=Springer |isbn=978-1-4419-8981-9 |page=240 |quote=For example, wing and haltere are homologous, yet widely divergent, organs that normally arise as dorsal appendages of the second thoracic (T2) and third thoracic (T3) segments, respectively.}}</ref>

Aside from the aforementioned double pair of wings found in insects, other examples of homology include the forearm structure of tetrapod limbs, this is perhaps the most famous example of homology, and is featured in many textbooks. The flippers of dolphins, the wings of bats and birds, and the arms and grasping hands of humans are all homologous to each other, each resulting from a shared ancestor akin to something like ''[[Acanthostega gunnari]]'' or the famous "fishapod" ''[[Tiktaalik]]''.<ref>{{Cite journal | last1=Scotland | first1=R. W. | title=Deep homology: A view from systematics | journal=BioEssays | volume=32 | issue=5 | pages=438–449 | year=2010 | pmid=20394064}}</ref>
===Difference between homology and analogy===
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While homology and analogy both concern themselves with similarities, the former differs from the latter in that homology refers to any similar structure found in related taxa that has been inherited as a result of common descent, whereas analogy refers to similar structures that have been derived independently of one another in different, unrelated taxa.<ref>"[https://explainry.com/homologous-analogous-structures/ Homologous and analogous structures: What's the difference?]"</ref>

==Science==
The field of [[evolutionary developmental biology]] can identify homologous structures found present during the development of the fetus in the womb. While it's not true that "ontogeny recapitulates phylogeny" as {{wpl|Haeckel}} so famously put it, it is true that similar stages of development can be found during embryonic genesis among various closely related taxa. These include the presence of budding limbs in [[snake]] embryos and the presence of budding teeth in the embryos of baleen whales.<ref>{{cite web |title=Homologies: developmental biology |url=http://evolution.berkeley.edu/evolibrary/article/lines_07 |publisher=UC Berkeley |accessdate=15 December 2016}}</ref> 

In addition, it has been found that there are deep homologies present in the very genomes of disparately related taxa, these genes are highly ancient, and determine growth patterns for many different taxa, demonstrating that structures once thought to be purely analogous turn out to be homologous to some extent after all.<ref name="Stanislav">{{cite journal |title=Squid Pax-6 and eye development | first=Stanislav I. |last=Tomarev |first2=Patrick |last2=Callaerts |first3=Lidia |last3=Kos |first4=Rina |last4=Zinovieva |first5=Georg |last5=Halder |first6=Walter |last6=Gehring |first7=Joram |last7=Piatigorsky | year=1997 |journal=Proceedings of the National Academy of Sciences |volume=94 |issue=6 |pages=2421–2426 | pmid=9122210}}</ref> These genes also demonstrate that the highly diverse range of [[eye]] morphology present in the [[animal]] kingdom come from a single common ancestor dating back many hundreds of millions of years, and that eye formation is dictated by one of these ancient genes, the gene in question being called ''Pax6'' and its variants.<ref name="Stanislav" />

==References==
{{reflist}}

[[Category:Biology]]
[[Category:Anatomy]]

Categories: Biology, Anatomy