Editing Class (biology) (section)

==History==
The class as a distinct rank of biological classification having its own distinctive name – and not just called a ''top-level genus'' ''(genus summum)'' – was first introduced by [[France|French]] [[botanist]] [[Joseph Pitton de Tournefort]] in the classification of plants that appeared in his ''[[Eléments de botanique]]'' of 1694.

Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct ''grade'' of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct ''type'' of construction, which is to say a particular layout of organ systems.<ref>{{cite book |last=Huxley |first=Thomas Henry |author-link=Thomas Huxley |editor-last=Henfrey |editor-first=Arthur |title=Scientific memoirs, selected from the transactions of foreign academies of science, and from foreign journals. Natural history |url=https://www.biodiversitylibrary.org/item/70597#page/186/mode/1up |publisher=Taylor and Francis |year=1853 |doi=10.5962/bhl.title.28029}}</ref> This said, the composition of each class is ultimately determined by the subjective judgment of [[taxonomist]]s.

In the first edition of his ''[[Systema Naturae]]'' (1735),<ref>[[Ernst Mayr|Mayr E.]] (1982). ''The Growth of Biological Thought''. Cambridge: The Belknap Press of Harvard University Press. {{ISBN|0-674-36446-5}}</ref> [[Carl Linnaeus]] divided all three of his [[Kingdom (biology)|kingdoms]] of nature ([[mineral]]s, [[plant]]s, and [[animal]]s) into classes. Only in the animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a [[Convenience|convenient]] "artificial key" according to his ''[[Linnaean taxonomy#Classification of plants|Systema Sexuale]]'', largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the [[APG system]] in 1998, which proposed a taxonomy of the [[flowering plant]]s up to the level of orders, many sources have preferred to treat ranks higher than orders as informal [[clade]]s. Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders.<ref>{{citation |last=Chase |first=Mark W. |last2=Reveal |first2=James L. |year=2009 |title=A phylogenetic classification of the land plants to accompany APG III |journal=Botanical Journal of the Linnean Society |volume=161 |issue=2 |pages=122–127 |doi=10.1111/j.1095-8339.2009.01002.x |name-list-style=amp |doi-access=free}}</ref>

The class was considered the highest level of the taxonomic hierarchy until [[George Cuvier]]'s ''embranchements'', first called [[Phylum|Phyla]] by [[Ernst Haeckel]],<ref>Collins, A.G., Valentine, J.W. (2001). [http://si-pddr.si.edu/jspui/bitstream/10088/7403/1/Collins_Valentine_EvDev2001.pdf "Defining phyla: evolutionary pathways to metazoan body plans"] {{webarchive |url=https://web.archive.org/web/20200427032535/https://repository.si.edu/handle/10088/7403 |date=2020-04-27}}. ''Evol. Dev''. '''3''': 432–442.</ref> were introduced in the early nineteenth century.