Life Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! == Classification == {{Main|Biological classification}} === Antiquity === {{main|Aristotle's biology}} The first classification of organisms was made by the Greek philosopher Aristotle (384β322 BC), who grouped living things as either plants or animals, based mainly on their ability to move. He distinguished animals with blood from animals without blood, which can be compared with the concepts of [[vertebrate]]s and [[invertebrate]]s respectively, and divided the blooded animals into five groups: viviparous quadrupeds ([[mammal]]s), oviparous quadrupeds (reptiles and [[amphibian]]s), birds, fishes and [[Cetacea|whales]]. The bloodless animals were divided into five groups: [[cephalopod]]s, [[crustacean]]s, insects (which included the spiders, [[scorpion]]s, and [[centipede]]s), shelled animals (such as most [[mollusc]]s and [[echinoderm]]s), and "[[zoophyte]]s" (animals that resemble plants). This theory remained dominant for more than a thousand years.<ref>{{Cite web |url=http://www.ucmp.berkeley.edu/history/aristotle.html |title=Aristotle |publisher=University of California Museum of Paleontology |access-date=15 November 2016 |url-status=dead |archive-url=https://web.archive.org/web/20161120124920/http://www.ucmp.berkeley.edu/history/aristotle.html |archive-date=20 November 2016}}</ref> === Linnaean === In the late 1740s, [[Carl Linnaeus]] introduced his system of [[binomial nomenclature]] for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning.<ref>{{Cite journal |author1-last=Knapp |author1-first=Sandra |author1-link=Sandra Knapp |author2-last=Lamas |author2-first=Gerardo |author3-last=Lughadha |author3-first=Eimear Nic |author4-last=Novarino |author4-first=Gianfranco |title=Stability or stasis in the names of organisms: the evolving codes of nomenclature |journal=[[Philosophical Transactions of the Royal Society of London B]] |volume=359 |issue=1444 |pages=611β622 |date=April 2004 |pmid=15253348 |pmc=1693349 |doi=10.1098/rstb.2003.1445}}</ref> The fungi were originally treated as plants. For a short period Linnaeus had classified them in the taxon [[Vermes]] in Animalia, but later placed them back in Plantae. [[Herbert Copeland]] classified the Fungi in his [[Protoctista]], including them with single-celled organisms and thus partially avoiding the problem but acknowledging their special status.<ref>{{Cite journal |title=The Kingdoms of Organisms |journal=Quarterly Review of Biology |volume=13|issue=4 |doi=10.1086/394568 |year=1938 |page=383 | last1 = Copeland | first1 = Herbert F.|s2cid=84634277 }}</ref> The problem was eventually solved by [[Robert Whittaker (ecologist)|Whittaker]], when he gave them their own [[Kingdom (biology)|kingdom]] in his [[five-kingdom system]]. [[Evolutionary history of life|Evolutionary history]] shows that the fungi are more closely related to animals than to plants.<ref>{{Cite journal |last1=Whittaker |first1=R.H. |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=3863 |pages=150β160 |date=January 1969 |pmid=5762760 |doi=10.1126/science.163.3863.150 |bibcode=1969Sci...163..150W |citeseerx=10.1.1.403.5430}}</ref> As advances in [[microscopy]] enabled detailed study of [[cell (biology)|cells]] and microorganisms, new groups of life were revealed, and the fields of [[cell biology]] and [[microbiology]] were created. These new organisms were originally described separately in [[protozoa]] as animals and [[thallophyte|protophyta/thallophyta]] as plants, but were united by [[Ernst Haeckel]] in the kingdom [[Protista]]; later, the [[prokaryote]]s were split off in the kingdom [[Monera]], which would eventually be divided into two separate groups, the Bacteria and the [[Archaea]]. This led to the [[six-kingdom system]] and eventually to the current [[three-domain system]], which is based on evolutionary relationships.<ref name="Woese1990"/> However, the classification of eukaryotes, especially of protists, is still controversial.<ref name="Adl 05">{{Cite journal |last1=Adl |first1=S.M. |last2=Simpson |first2=A.G. |last3=Farmer |first3=M.A. |title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists |journal=Journal of Eukaryotic Microbiology |volume=52 |issue=5 |pages=399β451 |year=2005 |pmid=16248873 |doi=10.1111/j.1550-7408.2005.00053.x|s2cid=8060916 |doi-access=free }}</ref> As microbiology developed, viruses, which are non-cellular, were discovered. Whether these are considered alive has been a matter of debate; viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses have been classed into "species" based on their [[genetics]], but many aspects of such a classification remain controversial.<ref>{{Cite journal |last=Van Regenmortel |first=M.H. |title=Virus species and virus identification: past and current controversies |journal=Infection, Genetics and Evolution |volume=7 |issue=1 |pages=133β144 |date=January 2007 |pmid=16713373 |doi=10.1016/j.meegid.2006.04.002|s2cid=86179057 }}</ref> The original Linnaean system has been modified many times, for example as follows:<!--the table is potentially highly misleading: it is not the case that Cavalier-Smith represents the latest thinking and indeed his classification of the Eukaryotes is not widely accepted--> {{Biological systems}} The attempt to organise the Eukaryotes into a small number of kingdoms has been challenged. The Protozoa do not form a [[clade]] or natural grouping<!--i.e. they're polyphyletic or paraphyletic-->,<ref name="SimpsonRoger2004">{{cite journal |title=The real 'kingdoms' of eukaryotes |last1=Simpson |first1=Alastair G.B. |last2=Roger |first2=Andrew J. |journal=[[Current Biology]] |volume=14 |issue=17 |pages=R693βR696 |doi=10.1016/j.cub.2004.08.038 |pmid=15341755|year=2004 |s2cid=207051421 |doi-access=free}}</ref> and nor do the [[Chromista]] (Chromalveolata).<ref>{{cite journal |last1=Harper |first1=J.T. |last2=Waanders |first2=E. |last3=Keeling |first3=P.J. |year=2005 |title=On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes |journal=[[International Journal of Systematic and Evolutionary Microbiology]] |volume=55 |issue=Pt 1 |pmid=15653923 |pages=487β496 |doi=10.1099/ijs.0.63216-0 |df=dmy-all |doi-access=free}}</ref> === Metagenomic === The ability to sequence large numbers of complete [[genome]]s has allowed biologists to take a [[Metagenomics|metagenomic]] view of the [[phylogeny]] of the whole [[Tree of life (biology)|tree of life]]. This has led to the realisation that the majority of living things are bacteria, and that all have a common origin.<ref name="Woese1990"/><!--"Woese1990" is defined in {{biological systems}}--yes, I know what you think of that--><ref name="NM-20160411">{{cite journal |last1=Hug |first1=Laura A. |last2=Baker |first2=Brett J. |last3=Anantharaman |first3=Karthik |last4=Brown |first4=Christopher T. |last5=Probst |first5=Alexander J. |last6=Castelle |first6=Cindy J. |last7=Butterfield |first7=Cristina N. |last8=Hernsdorf |first8=Alex W. |last9=Amano |first9=Yuki |last10=Ise |first10=Kotaro |last11=Suzuki |first11=Yohey |last12=Dudek |first12=Natasha |last13=Relman |first13=David A. |last14=Finstad |first14=Kari M. |last15=Amundson |first15=Ronald |date=11 April 2016 |title=A new view of the tree of life |journal=[[Nature Microbiology]] |volume=1 |issue=5 |at=16048 |doi=10.1038/nmicrobiol.2016.48 |pmid=27572647 |doi-access=free |last16=Thomas |first16=Brian C. |last17=Banfield |first17=Jillian F.}}</ref> <gallery class=center mode="nolines" heights="300" widths="300">File:Phylogenetic tree of life LUCA.svg|[[Phylogenetic]] tree based on [[rRNA]] [[gene]]s data (Woese ''et al.'', 1990)<ref name="Woese1990"/> showing the 3 life [[Domain (biology)|domains]], with the [[last universal common ancestor|last universal common ancestor (LUCA)]] at its root File:A Novel Representation Of The Tree Of Life.png|A 2016 [[Metagenomics|metagenomic]] representation of the [[Tree of life (biology)|tree of life]], unrooted, using [[ribosomal protein]] sequences. Bacteria are at top (left and right); [[Archaea]] at bottom; [[Eukaryote]]s in green at bottom right.<ref name="NM-20160411"/> </gallery> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page