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{{Grups taxonòmics}}
En [[biologia]], un '''regne''' és un [[rang taxonòmic]] cada una de les grans subdivisions en què es consideren distribuïts els éssers vius, basant-se en les seves característiques comunes.
Com a rang taxonòmic és tradicionalment el rang superior i en el més recent sistema dels tres dominis, el rang zoològic sota el [[domini (biologia)|domini]] biològic.
Els regnes es divideixen en grups més petits anomenats [[fílum]]s (en [[zoologia]]) o divisions in [[botànica]]. La seqüència completa de rangs és [[vida]], [[domini (biologia)|domini]], regne, [[fílum]], [[classe (biologia)|classe]], [[ordre (biologia)|ordre]], [[família (biologia)|família], [[gènere (biologia)|gènere]], i [[espècie]].
Actualment als [[Estats Units]] pocs llibres de text utilitzen el sistema de sis regnes ([[Animalia]], [[Plantae]], [[Fungi]], [[Protista]], [[Archaea]], [[Bacteria]]) mentre que a Gran bretanya, Austràlia i Colòmbia els llibres de text poden descriure cinc regnes ([[Animalia]], [[Plantae]], [[Fungi]], [[Protista]], i [[Prokaryota]] o [[Monera]]).
Històricament el nombre de regnes acceptats ha crescut de dos a sis. Tanmateix la recerca [[filogenètica]] de l'any 2000 cap enllà no recolza cap dels sistemes tradicionals.
==Dos regnes==
La classificació dels éssers vius entre animals i plantes és la més antiga. [[Aristòtil]] (384 aC–322 aC) classificà les espècies animals en el seu llibre [[Història dels animals]], i el seu deixeble [[Teofrast]] (cap a 371–c. 287 aC) escriví un llibre similar en paral·lel ([[Historia Plantarum|Història de les plantes]]).<ref>{{Citation |last=Singer |first=Charles J. |year=1931 |title=A short history of biology, a general introduction to the study of living things |publication-place=Oxford |publisher=Clarendon Press |oclc=1197036 }}</ref>
[[Carolus Linnaeus]] (1707–1778) va fer els fonaments de la moderna [[nomenclatura biològica]], actualment regulada en codis de nomenclatura. Distingí dos regnes d'éssers vius: ''Regnum Animale'' ('regne animal') per als [[animal]]s i ''Regnum Vegetabile'' ('regne dels vegetals') per a les [[plantes]]. (Linnaeus també va incloure els [[mineral]]s, ubicant-los en en tercer regne, ''[[Mineralia|Regnum Lapideum]]''.) Linnaeus dividí cada regne eb tres classes, més tard agrupats en [[fílum|phyla]] per als animals i [[Divisió (biologia)|divisions]] per a les plantes.
{{clade
|1={{clade
|label1=life
|1={{clade
|1=Regnum Vegetabile
|2=Regnum Animale
}}
}}
}}
==Tres regnes==
El 1674, [[Antonie van Leeuwenhoek]], sovint anomenat el "pare de la microscopia", envià a la [[Royal Society]] de Londres una còpia de les seves primeres observacions al microscopi d'organismes unicel·lulars. Fins aquell moment s'ignorava completament que aquells organismes microscopics existissin. De primer aquests organismes es van dividir entre animals i plantes i ubicats en el seu regne apropiat. Tanmateix cap a la meitat dle segle XIX va quedar cklar que "la dicotomia existent entre els regnes de les plantes i dels animals [havia passat] ràpidament a ser borrosa i els seus límits passats de moda".<ref name=Scamardella1999>{{Citation |last=Scamardella |first=Joseph M. |year=1999 |title=Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista |journal=International Microbiology |volume=2 |pages=207–16 |pmid=10943416 |issue=4 }}</ref> El 1866, seguint les propostes de [[Richard Owen]] i [[John Hogg]], [[Ernst Haeckel]] proposà un tercer regne de la vida. Haeckel revisà el contingut d'aquest regne moltes vegades abans d'encabir-lo en una divisió basada en quins organismes eren unicel·lulars (Protista) o pluricel·lulars (animals i plantes).<ref name=Scamardella1999/>
{{clade
|1={{clade
|label1=life
|1={{clade
|1=Kingdom Protoctista
|2=Kingdom Plantae
|3=Kingdom Animalia
}}
}}
}}
==Quatre regnes==
El desenvolupament del microscopi i el [[microscopi electrònic]] en particular, revelaren una distinció important entre els organismes que eren unicel·lulars les cèl·lules dels quals no tenien nucli diferenciat [[procariote]]s, i aquells organismes unicel·lulars o plurice·lulars que sí que en tenien [[eucariote]]s. Elà una classificació en quatre regnes, desplaçant els dos grups procariotes, bacteris i ''algues blaves'', en un regne separat '''Monera'''.<ref name=Scamardella1999/>
{{clade
|1={{clade
|label1=life
|1={{clade
|1=Kingdom Monera (procariotes, és a dir bacteris i "algues blaves")
|2=Kingdom Protista (eucariotes unicel·lulars)
|3=Kingdom Plantae
|4=Kingdom Animalia
}}
}}
}}
<!--
It gradually became apparent how important the prokaryote/eukaryote distinction is, and Stanier and van Niel popularized [[Édouard Chatton]]'s proposal in the 1960s to recognize this division in a formal classification. This required the creation, for the first time, of a rank above kingdom, a superkingdom or empire.<ref name="Stanier">{{Citation |last=Stanier |first=R.Y. |last2=Van Neil |first2=C.B. |year=1962 |title=The concept of a bacterium |journal=Archiv Für Mikrobiologie |volume=42 |pages=17–35 |pmid=13916221 |lastauthoramp=yes |doi=10.1007/BF00425185 }}</ref>
{{clade
|1={{clade
|label1=life
|1={{clade
|1={{clade
|label1=Empire Prokaryota
|1={{clade
|1=Kingdom Monera
}}
}}
|2={{clade
|label1=Empire Eukaryota
|1={{clade
|1=Kingdom Protista
|2=Kingdom Plantae
|3=Kingdom Animalia
}}
}}
}}
}}
}}
==Five kingdoms== <!-- This section is linked from [[Monera]] -->
The differences between [[fungi]] and other organisms regarded as plants had long been recognized. For example, at one point Haeckel moved the fungi out of Plantae into Protista, before changing his mind.<ref name=Scamardella1999/> [[Robert Whittaker]] recognized an additional kingdom for the [[Fungus|Fungi]]. The resulting five-kingdom system, proposed in 1969, has become a popular standard and with some refinement is still used in many works and forms the basis for newer multi-kingdom systems. It is based mainly on differences in [[nutrition]]; his Plantae were mostly multicellular [[autotroph]]s, his Animalia multicellular [[heterotroph]]s, and his Fungi multicellular [[saprotroph]]s. The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies.<ref name="Whittaker1969">{{Citation |last=Whittaker |first=R.H. |year=1969 |title=New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms |journal=Science |volume=163 |issue=863 |pages=150–60 |url=http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=5762760 |month=January |pmid=5762760 }}</ref> The five kingdom system may be combined with the two empire system.
{{clade
|1={{clade
|label1=life
|1={{clade
|1={{clade
|label1=Empire Prokaryota
|1={{clade
|1=Kingdom Monera
}}
}}
|2={{clade
|label1=Empire Eukaryota
|1={{clade
|1=Kingdom Protista
|2=Kingdom Plantae
|3=Kingdom Fungi
|4=Kingdom Animalia
}}
}}
}}
}}
}}
==Six kingdoms==<!-- This section is linked from [[Monera]] -->
From around the mid-1970s onwards, there was an increasing emphasis on molecular level comparisons of genes (initially [[ribosome|ribosomal]] [[RNA]] genes) as the primary factor in classification; genetic similarity was stressed over outward appearances and behavior. Taxonomic ranks, including kingdoms, were to be groups of organisms with a common ancestor, whether [[monophyletic]] (''all'' descendants of a common ancestor) or [[paraphyletic]] (only some descendants of a common ancestor). Based on such RNA studies, [[Carl Woese]] divided the prokaryotes (Kingdom Monera) into two groups, called [[bacterium|Eubacteria]] and [[Archaea|Archaebacteria]], stressing that there was as much genetic difference between these two groups as between either of them and all eukaryotes. Eukaryote groups, such as plants, fungi and animals may look different, but are more similar to each other in their genetic makeup at the molecular level than they are to either the Eubacteria or Archaebacteria. (It was also found that the eukaryotes are more closely related, genetically, to the Archaebacteria than they are to the Eubacteria.) Woese attempted to establish a "three primary kingdom" or "urkingdom" system.<ref name="Woese1977">{{Citation |last=Balch |first=W.E. |last2=Magrum |first2=L.J. |last3=Fox |first3=G.E. |last4=Wolfe |first4=C.R. |year=1977 |title=An ancient divergence among the bacteria |journal=J. Mol. Evol. |volume=9 |issue=4 |pages=305–11 |doi=10.1007/BF01796092 |coauthors=& Woese, C.R. |month=August |pmid=408502 }}</ref> In 1990, the name "domain" was proposed for the highest rank.<ref>{{Citation |last=Woese |first=C.R. |last2=Kandler |first2=O. |last3=Wheelis |first3=M. |year=1990 |title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya |journal=Proc Natl Acad Sci U S A |volume=87 |issue=12 |pages=4576–9 |doi=10.1073/pnas.87.12.4576 |pmid=2112744 |pmc=54159 |lastauthoramp=yes }}</ref> The six-kingdom system shown below represents a blending of the classic five-kingdom system and Woese's [[three-domain system]]. Such six-kingdom systems have become standard in many works.
{{clade
|1={{clade
|label1=life
|1={{clade
|1={{clade
|label1=Domain Bacteria
|1={{clade
|1=Kingdom Bacteria
}}
}}
|2={{clade
|label1=Domain Archaea
|1={{clade
|1=Kingdom Archaea
}}
}}
|3={{clade
|label1=Domain Eukarya
|1={{clade
|1=Kingdom Protista
|2=Kingdom Plantae
|3=Kingdom Fungi
|4=Kingdom Animalia
}}
}}
}}
}}
}}
Woese also recognized that the Protista kingdom was not a monophyletic group and might be further divided at the level of kingdom.
==Cavalier-Smith's six kingdoms==
[[Thomas Cavalier-Smith]] has published extensively on the evolution and classification of life, particularly protists. His views have been influential but controversial, and not always widely accepted.<ref>{{Citation |last=Palaeos.com |title=Origins of the Eukarya |url=http://www.palaeos.com/Eukarya/Eukarya.html |accessdate=2010-04-29 |archiveurl=http://www.webcitation.org/5pLfYf6U7 |archivedate=2010-04-29 }}</ref> In 1998, he published a six-kingdom model,<ref>{{Citation |last=Cavalier-Smith |first=T. |year=1998 |title=A revised six-kingdom system of life |journal=Biological Reviews |volume=73 |pages=203–66 |url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=685 |issue=03 |doi=10.1017/S0006323198005167 }}</ref> which has been revised in subsequent papers. The version published in 2004 is shown below.<ref name="CavalierSmith2004">{{Citation |last=Cavalier-Smith |first=T. |year=2004 |title=Only six kingdoms of life |journal=Proc. R. Soc. Lond. B |volume=271 |pages=1251–62 |url=http://www.cladocera.de/protozoa/cavalier-smith_2004_prs.pdf |accessdate=2010-04-29 |doi=10.1098/rspb.2004.2705 |pmid=15306349 |issue=1545 |pmc=1691724 }}</ref> Cavalier-Smith does not accept the importance of the fundamental eubacteria–archaebacteria divide put forward by Woese and others. His Kingdom Bacteria includes the Archaebacteria as part of a subkingdom along with a group of eubacteria (Posibacteria).>-->
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