View source for Polyphyly

{{short description|Property of a group not united by common ancestry}}
[[File:Clade-grade II.svg|thumb|300px|In this [[phylogenetic tree]], the blue and red groups (which are both ''monophyletic'') do not share an immediate common ancestor. If they are grouped together because they share characteristics which appear to be similar, then their combination forms a ''polyphyletic group''.]]
[[File:Monophyly, paraphyly, polyphyly.svg|thumb|300px|[[Cladogram]] of the [[primate]]s, showing a [[monophyly]] (the simians, in yellow), a [[paraphyly]] (the prosimians, in cyan, including the red patch), and a polyphyly (the night-active primates, the [[loris]]es and the [[tarsier]]s, in red).]]
[[File:Phylogenetic-Groups.svg|thumbnail|300px|Phylogenetic groups: A monophyletic taxon (in yellow, the clade [[Sauropsida]] grouping "reptiles and birds") contains a common ancestor and all of its descendants. A paraphyletic taxon (in cyan, the "reptiles") contains its most recent common ancestor, but does not contain all the descendants of that ancestor. A polyphyletic taxon (in red, the group [[Haemothermia]] containing [[Homeothermy|warm-blooded tetrapods]]) does not contain the most recent common ancestor of all its members.]]

A '''polyphyletic''' group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor.<ref>{{Cite book |last=Urry |first=Lisa A. |title=Campbell Biology |publisher=Pearson |year=2016 |isbn=978-0-134-09341-3 |edition=11th |pages=558}}</ref> The term is often applied to groups that share similar features known as [[Homoplasy|homoplasies]], which are explained as a result of [[convergent evolution]]. The arrangement of the members of a polyphyletic group is called a '''polyphyly''' {{IPAc-en|ˈ|p|ɒ|l|ɪ|ˌ|f|aɪ|l|i}}.<ref name="OED">{{Cite OED|polyphyly|access-date = 28 December 2021}}. [Source for pronunciation.]</ref> It is contrasted with [[monophyly]] and [[paraphyly]].

For example, the biological characteristic of [[warm-blooded]]ness evolved separately in the ancestors of mammals and the ancestors of birds; "warm-blooded animals" is therefore a polyphyletic grouping.<ref>{{Cite book |last=Archibald |first=J. David |url=https://books.google.com/books?id=VgkZBQAAQBAJ&pg=PA162 |title=Aristotle's Ladder, Darwin's Tree: The Evolution of Visual Metaphors for Biological Order |date=2014-07-15 |publisher=[[Columbia University Press]] |isbn=9780231164122 |language=en}}</ref> Other examples of polyphyletic groups are [[algae]], [[C4 photosynthesis|C4 photosynthetic plants]],<ref name="Sage-2004">{{Cite journal|last=Sage|first=Rowan F.|date=2004-02-01|title=The evolution of C4 photosynthesis |journal=[[New Phytologist]] |language=en |volume=161 |issue=2 |pages=341–370 |doi=10.1111/j.1469-8137.2004.00974.x |pmid=33873498 |issn=1469-8137|doi-access=free}}</ref> and [[Xenarthra#Evolutionary relationships|edentates]].<ref name="Delsuc2008">{{Cite book |last1=Delsuc |first1=Frédéric |title=The biology of the Xenarthra |last2=Douzery |first2=Emmanuel J. P. |publisher=[[University Press of Florida]] |year=2008 |isbn=9780813031651 |editor-last1=Vizcaíno |editor-first1=Sergio F. |location=Gainesville |pages=11–23 |chapter=Recent advances and future prospects in xenarthran molecular phylogenetics |oclc=741613153 |editor-last2=Loughry |editor-first2=W. J.}}</ref>

Many [[taxonomist]]s aim to avoid homoplasies in grouping taxa together, with a goal to identify and eliminate groups that are found to be polyphyletic. This is often the stimulus for major revisions of the classification schemes. Researchers concerned more with ecology than with systematics may take polyphyletic groups as legitimate subject matter; the similarities in activity within the fungus group ''[[Alternaria]]'', for example, can lead researchers to regard the group as a valid [[genus]] while acknowledging its polyphyly.<ref>{{cite journal |first1=Erik T. |last1=Aschehoug |first2=Kerry L. |last2=Metlen |first3=Ragan M. |last3=Callaway |first4=George |last4=Newcombe |year=2012 |title=Fungal endophytes directly increase the competitive effects of an invasive forb |journal=Ecology |volume=93 |issue=1 |pages=3–8 |doi=10.1890/11-1347.1 |pmid=22486080 |doi-access=free |bibcode=2012Ecol...93....3A }}</ref> In recent research, the concepts of monophyly, paraphyly, and polyphyly have been used in deducing key genes for [[DNA barcoding|barcoding]] of diverse groups of species.<ref>{{cite journal |doi=10.1016/j.gene.2019.143967 |pmid=31279710 |title=Diagnosis of mitogenome for robust phylogeny: A case of Cypriniformes fish group |journal=Gene |volume=713 |pages=143967 |year=2019 |last1=Parhi J., Tripathy P.S., Priyadarshi, H. |first1=Mandal S.C., Pandey P.K. |s2cid=195828782 }}</ref>

== Etymology ==
The term ''polyphyly'', or ''polyphyletic'', derives from the two [[ancient greek|Ancient Greek]] words {{wikt-lang|grc|πολύς}} ({{grc-transl|πολύς}}) 'many, a lot of', and {{wikt-lang|grc|φῦλον}} ({{grc-transl|φῦλον}}) 'genus, species',<ref name="Bailly1981">{{Cite book |last=Bailly |first=Anatole |title=Abrégé du dictionnaire grec français |date=1981-01-01 |publisher=[[Hachette (publisher)|Hachette]] |isbn=978-2010035289 |location=Paris |oclc=461974285}}</ref><ref name="Tabularium">{{Cite web |url=http://www.tabularium.be/bailly/ |title=Greek-French dictionary online |last=Bailly |first=Anatole |website=www.tabularium.be |access-date=March 2, 2018}}</ref> and refers to the fact that a polyphyletic group includes organisms (e.g., genera, species) arising from ''multiple'' ancestral sources.

Conversely, the term ''[[monophyly]]'', or ''monophyletic'', employs the ancient Greek adjective {{wikt-lang|grc|μόνος}} ({{grc-transl|μόνος}}) 'alone, only, unique',<ref name="Bailly1981"/><ref name="Tabularium"/> and refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a ''unique'' common ancestor.

By comparison, the term ''[[paraphyly]]'', or ''paraphyletic'', uses the ancient Greek preposition {{wikt-lang|grc|παρά}} ({{grc-transl|παρά}}) 'beside, near',<ref name="Bailly1981"/><ref name="Tabularium"/> and refers to the situation in which one or several monophyletic subgroups are ''left apart'' from all other descendants of a unique common ancestor.

== Avoidance ==
{{See also|Phylogenetic nomenclature#Philosophy}}

In many schools of [[Taxonomy (biology)|taxonomy]], the recognition of polyphyletic groups in a classification is discouraged. [[Monophyletic]] groups (that is, [[clades]]) are considered by these schools of thought to be the only valid groupings of [[organism]]s because they are diagnosed ("defined", in common parlance) on the basis of [[synapomorphy|synapomorphies]], while paraphyletic or polyphyletic groups are not.  From the perspective of ancestry, clades are simple to define in purely [[Phylogenetics|phylogenetic]] terms without reference to clades previously introduced: a [[Phylogenetic nomenclature#Phylogenetic definitions of clade names|node-based clade definition]], for example, could be "All descendants of the last common ancestor of species X and Y". On the other hand, polyphyletic groups can be delimited as a conjunction of several clades, for example "the flying vertebrates consist of the bat, bird, and pterosaur clades".

From a practical perspective, grouping species monophyletically facilitates prediction far more than does polyphyletic grouping. For example, classifying a newly discovered grass in the monophyletic family [[Poaceae]], the true grasses, immediately results in numerous predictions about its structure and its developmental and reproductive characteristics, that are synapomorphies of this family. In contrast, Linnaeus' assignment of plants with two [[stamen]]s to the polyphyletic class Diandria, while practical for identification, turns out to be useless for prediction, since the presence of exactly two stamens has developed convergently in many groups.<ref>{{cite journal |first=Clive A. |last=Stace |author-link=Clive A. Stace |year=2010 |title=Classification by molecules: What's in it for field botanists? |journal=Watsonia |volume=28 |pages=103–122 |url=http://www.archive.bsbi.org.uk/Wats28p103.pdf |access-date=July 31, 2013 |archive-url=https://web.archive.org/web/20121015135726/http://archive.bsbi.org.uk/Wats28p103.pdf |archive-date=October 15, 2012 |url-status=dead |df=mdy-all }}</ref>

== Polyphyletic species ==
[[Species]] have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification.<ref>{{cite journal|last1=Queiroz|first1=Kevin|last2=Donoghue|first2=Michael J.|title=Phylogenetic Systematics and the Species Problem|journal=Cladistics|date=December 1988|volume=4|issue=4|pages=317–338|doi=10.1111/j.1096-0031.1988.tb00518.x|pmid=34949064 |s2cid=40799805}}</ref> It is usually implicitly assumed that species are monophyletic (or at least [[paraphyletic]]). However, [[hybrid speciation]] arguably leads to polyphyletic species.<ref>{{Cite journal|last1=Hörandl |first1=E. |last2=Stuessy |first2=T.F.|title=Paraphyletic groups as natural units of biological classification|journal=Taxon|date=2010|volume=59|issue=6|pages=1641–1653|doi=10.1002/tax.596001 |bibcode=2010Taxon..59.1641H }}</ref> Hybrid species are a common phenomenon in nature, particularly in plants where [[polyploidy]] allows for rapid speciation.<ref>{{cite journal|last=Linder|first=C.R.|author2=Risenberg, L.H.|title=Reconstructing patterns of reticulate evolution in plants|journal=American Journal of Botany|date=22 June 2004|volume=91|pages=1700–1708|issue=10|doi=10.3732/ajb.91.10.1700|pmid=18677414|pmc=2493047|bibcode=2004AmJB...91.1700L }}</ref> Some [[Cladistics|cladist]] authors do not consider species to possess the property of "-phyly", which they assert applies only to groups of species.<ref>{{Cite journal |last1=Nixon |first1=Kevin C. |last2=Wheeler |first2=Quentin D. |date=September 1990 |title=An amplification of the phylogenetic species concept |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1096-0031.1990.tb00541.x |journal=Cladistics |language=en |volume=6 |issue=3 |pages=211–223 |doi=10.1111/j.1096-0031.1990.tb00541.x |issn=0748-3007}}</ref><ref>{{Cite book |last1=Brower |first1=Andrew V. Z. |title=Biological systematics: principles and applications |last2=Schuh |first2=Randall T. |date=2021 |publisher=Comstock Publishing Associates, an imprint of Cornell University Press |isbn=978-1-5017-5277-3 |edition=3 |location=Ithaca, New York}}</ref>

== See also ==
* [[Carcinisation]]
* [[Convergent evolution]]

== References ==
{{reflist}}

==Bibliography==
* {{RefTudgeVariety}}
* {{Cite web|url=http://www.blackwellpublishing.com/ridley/a-z/Polyphyletic_group.asp|title=Evolution - A-Z - Polyphyletic group|website=www.blackwellpublishing.com|access-date=2018-02-24}}

==External links==
* Funk, D. J., and Omland, K. E. (2003). "Species-level paraphyly and polyphyly: Frequency, cause and consequences, with insights from animal mitochondrial DNA" ''Annu. Rev. Ecol. Evol. Syst.'' '''34''': 397–423. at ftp://137.110.142.4/users/bhhanser/Subspecies%20general%20literature/FunkEtal2003AnnuRevEcolEvolV34pp397-423.pdf{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}

{{Phylogenetics}}

[[Category:Phylogenetics]]