View source for Systematics

{{Short description|Branch of biology}}
{{redirect|Systematic biology|the journal|Systematic Biology||Systematics (disambiguation)}}
[[File:Phylogenetics.svg|thumb|400px|A comparison of phylogenetic and phenetic (character-based) concepts]]
'''Systematics''' is the study of the diversification of living forms, both past and present, and the [[Correlation and dependence|relationships]] among living things through time. Relationships are visualized as evolutionary trees (synonyms: [[phylogenetic tree]]s, phylogenies).  Phylogenies have two components: branching order (showing group relationships, graphically represented in [[cladograms]]) and branch length (showing amount of evolution).  Phylogenetic trees of species and higher [[taxa]] are used to study the evolution of traits (e.g., anatomical or molecular characteristics) and the distribution of organisms ([[biogeography]]). Systematics, in other words, is used to understand the evolutionary history of life on Earth.

The word systematics is derived from the Latin word of Ancient Greek origin ''[[wikt:systema#Latin|systema]],'' which means systematic arrangement of organisms. [[Carl Linnaeus]] used '[[Systema Naturae]]' as the title of his book.

==Branches and applications==
In the study of biological systematics, researchers use the different branches to further understand the relationships between differing organisms. These branches are used to determine the applications and uses for modern day systematics.{{cn|date=June 2024}}

Biological systematics classifies species by using three specific branches. ''Numerical systematics'', or ''biometry'', uses biological statistics to identify and classify animals. ''Biochemical systematics'' classifies and identifies animals based on the analysis of the material that makes up the living part of a cell—such as the [[Cell nucleus|nucleus]], [[organelle]]s, and [[cytoplasm]]. ''Experimental systematics'' identifies and classifies animals based on the evolutionary units that comprise a species, as well as their importance in evolution itself. Factors such as mutations, genetic divergence, and hybridization all are considered evolutionary units.<ref name=":0">{{Cite news|url=http://www.biologydiscussion.com/animals-2/systematics-meaning-branches-and-its-application/32374|title=Systematics: Meaning, Branches and Its Application|date=2016-05-27|work=Biology Discussion|access-date=2017-04-12|language=en-US}}</ref>

With the specific branches, researchers are able to determine the applications and uses for modern-day systematics. These applications include:  
* Studying the diversity of organisms and the differentiation between extinct and living creatures. Biologists study the well-understood relationships by making many different diagrams and "trees" (cladograms, phylogenetic trees, phylogenies, etc.).  
* Including the scientific names of organisms, species descriptions and overviews, taxonomic orders, and classifications of evolutionary and organism histories.
* Explaining the biodiversity of the planet and its organisms. The systematic study is that of conservation.
* Manipulating and controlling the natural world. This includes the practice of 'biological control', the intentional introduction of natural predators and disease.<ref name=":0" />

==Definition and relation with taxonomy==

[[John Lindley]] provided an early definition of systematics in 1830, although he wrote of "systematic botany" rather than using the term "systematics".<ref>Wilkins, J. S. ''[http://evolvingthoughts.net/2011/02/what-is-systematics-and-what-is-taxonomy/ What is systematics and what is taxonomy?] {{Webarchive|url=https://web.archive.org/web/20160827124330/http://evolvingthoughts.net/2011/02/what-is-systematics-and-what-is-taxonomy/ |date=2016-08-27 }}''. Available on http://evolvingthoughts.net</ref>

In 1970  Michener ''et al.'' defined "systematic biology" and "[[Taxonomy (biology)|taxonomy]]" (terms that are often confused and used interchangeably) in relationship to one another as follows:<ref>Michener, Charles D., John O. Corliss, Richard S. Cowan, Peter H. Raven, Curtis W. Sabrosky, Donald S. Squires, and G. W. Wharton (1970). ''Systematics In Support of Biological Research''. Division of Biology and Agriculture, National Research Council. Washington, D.C. 25 pp.</ref>

<blockquote>
Systematic biology (hereafter called simply systematics) is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced a notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above.
</blockquote>

The term "taxonomy" was coined by [[Augustin Pyramus de Candolle]]<ref>{{Cite book |url= https://books.google.com/books?id=In_Lv8iMt24C&pg=PA20 |title=Plant systematics: An integrated approach |last=Singh |first=Gurcharan |date=2004 |publisher=Science Publishers |isbn=9781578083510 |page=20 |via=Google Books}}</ref> while the term "systematic" was coined by [[Carl Linnaeus]] the father of taxonomy.{{cn|date=June 2024}}

Taxonomy, systematic biology, systematics, biosystematics, scientific classification, biological classification, phylogenetics: At various times in history, all these words have had overlapping, related meanings.  However, in modern usage, they can all be considered synonyms of each other.

For example, Webster's 9th New Collegiate Dictionary of 1987 treats "classification", "taxonomy", and "systematics" as synonyms. According to this work, the terms originated in 1790, {{circa|1828}}, and in 1888 respectively. Some{{who|date=July 2013}} claim systematics alone deals specifically with relationships through time, and that it can be synonymous with [[phylogenetics]], broadly dealing with the inferred hierarchy{{citation needed|date=November 2014}} of organisms.  This means it would be a subset of taxonomy as it is sometimes regarded, but the inverse is claimed by others.{{who|date=July 2013}}

Europeans tend to use the terms "systematics" and "biosystematics" for the study of biodiversity as a whole, whereas North Americans tend to use "taxonomy" more frequently.<ref>Brusca, R. C., & Brusca, G. J. (2003). Invertebrates (2nd ed.). Sunderland, Mass. : Sinauer Associates, p. 27</ref> However, taxonomy, and in particular [[alpha taxonomy]], is more specifically the identification, description, and naming (i.e. nomenclature) of organisms,<ref name="Fortey">
{{Citation |last= Fortey |first= Richard |author-link= Richard Fortey
|year=2008
|title= Dry Store Room No. 1: The Secret Life of the Natural History Museum |location= London
|publisher= Harper Perennial |isbn= 978-0-00-720989-7
}}
</ref> while "classification" focuses on placing organisms within hierarchical groups that show their relationships to other organisms.  All of these biological disciplines can deal with both [[extinct]] and [[extant taxon|extant]] organisms.

Systematics uses taxonomy as a primary tool in understanding, as nothing about an organism's relationships with other living things can be understood without it first being properly studied and described in sufficient detail to identify and classify it correctly.<ref>{{cite journal
| last1 = Zhang
| first1 = G.
| last2 = Feng
| first2 = Q.
| year = 2025
| title = Why we should not describe new taxa without using phylogenetics. Comment on Chen et al. (2025)
| journal = Journal of Natural History
| volume = 59
| issue = 37–40
| pages = 2355–2359
| doi = 10.1080/00222933.2025.2564347
| url = https://doi.org/10.1080/00222933.2025.2564347
| url-access = subscription
}}</ref>  Scientific classifications are aids in recording and reporting information to other scientists and to laymen.  The '''systematist''', a scientist who specializes in systematics, must, therefore, be able to use existing classification systems, or at least know them well enough to skilfully justify not using them.

[[Phenetics]] was an attempt to determine the relationships of organisms through a measure of overall similarity, making no distinction between [[plesiomorph]]ies (shared ancestral traits) and [[apomorph]]ies (derived traits). From the late-20th century onwards, it was superseded by [[cladistics]], which rejects plesiomorphies in attempting to resolve the [[phylogeny]] of Earth's various organisms through time.  {{As of | 2014 | alt = Today's}} systematists generally make extensive use of [[molecular biology]] and of [[computer programs]] to study organisms.{{cn|date=June 2024}}

==Taxonomic characters==
Taxonomic characters are the taxonomic attributes that can be used to provide the evidence from which relationships (the [[phylogeny]]) between taxa  are inferred.<ref>Mayr, Ernst and Peter D. Ashlock (1991). Principles of Systematic Zoology, (2nd edn.) New York: McGraw-Hill, p. 159.</ref> Kinds of taxonomic characters include:<ref>Mayr, Ernst and Peter D. Ashlock (1991), p. 162.</ref>
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* Morphological characters
** General external morphology
** Special structures (e.g. genitalia)
** Internal morphology (anatomy)
** Embryology
** Karyology and other cytological factors
* Physiological characters
** Metabolic factors
** Body secretions
** Genic sterility factors
* Molecular characters
** Immunological distance
** Electrophoretic differences
** Amino acid sequences of proteins
** DNA hybridization
** DNA and RNA sequences
** Restriction endonuclease analyses
** Other molecular differences
{{col-break}}
* Behavioral characters
** Courtship and other ethological isolating mechanisms
** Other behavior patterns
* Ecological characters
** Habit and habitats
** Food
** Seasonal variations
** Parasites and hosts
* Geographic characters
** General biogeographic distribution patterns
** Sympatric-allopatric relationship of populations
{{col-end}}

==See also==
* [[Evolutionary systematics]] – a school of systematics
* [[Global biodiversity]]
* [[16S ribosomal RNA]] – an intensively studied nucleic acid that has been useful in phylogenetics
* [[Phylogenetic comparative methods]] – use of evolutionary trees in other studies, such as [[biodiversity]], comparative biology. adaptation, or evolutionary mechanisms
* [[Lichen systematics]]

== References ==
=== Notes ===
{{Reflist}}

=== Further reading ===
* Brower, Andrew V. Z. and Randall T. Schuh.  2021. ''Biological Systematics:  Principles and Applications, 3rd edn.''  {{ISBN|978-1-5017-5277-3}}
* Simpson, Michael G. 2005.  ''Plant Systematics''. {{ISBN|978-0-12-644460-5}}
* Wiley, Edward O. and Bruce S. Lieberman. 2011. "Phylogenetics: Theory and Practice of Phylogenetic Systematics, 2nd edn." {{ISBN|978-0-470-90596-8}}

== External links ==
* [http://www.sasb.org.au Society of Australian Systematic Biologists]
* [http://www.systbio.org/ Society of Systematic Biologists]
* [http://www.cladistics.org/ The Willi Hennig Society]

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[[Category:Evolutionary biology]]
[[Category:Biological classification]]
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