Taxonomy

Etymology

Taxonomie would originate in the Greek ταξινομία taxis , “placement”, “put in order” (and indirectly Sanskrit; taksh = “to cut”, “to make”, “to form”), and nomos which means “law”)

Differences between taxonomy and systematic

In the majority of the disciplines of the Life sciences, the taxonomy term is inseparable from that of systematic, science which has as an aim to count and to classify tax them in a certain order, based on various principles.

In practice, the “systematic” term as well indicates the method used (one will say for example “the systematic phylogenetic one”) that the result obtained with this method (the “systematic one of Agaricales”). In the concrete direction of result, two sciences not very distinct and are often confused, because practiced simultaneously by the same people. The taxinomists were from time immemorial appointed systematicians, because after having studied and described organizations, they quite naturally tried to classify them starting from the low level of the species ( alpha taxonomy or “primary taxonomy”).

Those which use especially the direction of method, the phylogeneticians in particular, often name the classification result or “taxonomy”.

History of taxonomy

The term was created in 1813, under the orthography of “taxonomy”, by the Swiss botanist Augustin Pyrame de Candolle (1778-1841) in its elementary Théorie of botany or exposure of the principles of natural classification and art to describe and study the plants , to indicate in its “theory of classifications” at the same time the method and what it described as “bases of philosophical botany” ( Mémoires and memories , Livre III, § 11).

Although, like the method of Jussieu, it uses the binomials linnéens and recommends the “natural method” opposed to the “artificial system” of Carl von Linné, the taxonomy suggested by Candolle deviates some by the importance given to the cuts. Whereas for Linné and Jussieu, nature “ does not make a jump ”, Candolle insists on discontinuities which are at the base of the concept of Taxon, at the same time entity and cut .

The term became of everyday usage today, either in the original C-W communication, but étymologiquement disputed, of taxonomy, or under the C-W communication corrected by Emile Littré of taxonomy, but the other C-W communication remains nevertheless very widespread, in particular because of its conservation in the English translation, taxonomy . On the etymological controversy, to see Fischer and Rey (1983) .

Origin and evolution of the models

All the Classification S are appeared as a tree (arborescent classification), since a root including all the alive beings existing or having existed, until the Individu S.

Each node of the tree defines a Taxon, which groups all under-tax them that the node generates.

But, in the past, it always was not thus. The Naturaliste Swedish Carl von Linné (1707 - 1778) posed the foundations of systematic, and was the author of a classification whose great principles were the base of the systematic scientist until the middle of the 20th century.

Systematic traditional (the sometimes known as “linnéenne”, whose hierarchical order interns Taxons was founded in the beginning on criteria of “morphological” resemblance and supposed affinities. Although strongly anthropocentric and reflecting causes of the diversity of the living beings (divine creation) such as one thought them here 250 years, it still makes, in this beginning of the 21e century, left the common cultural luggage of all the naturalists. But, progressively of advanced thereafter knowledge, in particular starting from work of Lamarck and Darwin, this order quickly had the ambition to give by addition an indication of the evolution.

The anthropocentrism was beaten in breach with Charles Darwin which recommends in 1859 purely a genealogical classification . If there were evolution, the species must be classified according to their degree of evolutionary political alliance. But it will be necessary to wait nearly one century so that we really arrive there, and initially so that us meanings the genealogy as inaccessible (which goes down from which?) for better concentrating us on the phylogeny (which is closer to which?).

In second half of the 20th century, systematic the known as phylogenetic one developed starting from a method of rebuilding which experienced a striking down development: the cladistique one, initiated by Hennig in 1950. This method is overall founded on evolutionary relations for which the fundamental criterion of the choice of classification is that it must reflect phylogeny strictly, i.e. the degrees of political alliance between species. The concept even of such a phylogeny is a consequence of the Théorie of the evolution, and the predictive success of the phylogenetic trees one of the evidence of this theory.

The current phylogenetic approach calls upon the data of the cladistique one, but its requirements are summarized not to accept that tax monophiletic, i.e. correspondent with a Clade given. She asks that tax them are limited to those which observe the two following conditions:

all the individuals of the taxon go down from a particular ancestral individual;
all the descendants of this particular ancestor are in the taxon.

One speaks then only about taxon monophyletic or clade. This constraint brought fundamental modifications of scientific classification, some reversing the “common direction” modelled by the cultural heritage. Thus the Dinosaure S do not have not disappeared, the systematic modern one including the Oiseau X in the grouping “dinosaurs”.

Among other examples, let us tax them traditional like reptiles , fish , algae , dicotylédones , pongidés , do not have established among into systematic phylogenetic, because not considered polyphyletic (multiple origins) or paraphyletic (incomplete). Others survived with some after-effects, like mushrooms . Lastly, some overcame the storm, like animal (Métazoaires) or mammalian . Let us notice that there was nothing obvious so that all the multicellular animals divide a common ancestor who separates them from any plant or mushroom.

Besides that, its structure remains basically of linnéen type and its nomenclature also.

There are several technical approaches to work out the phylogenetic trees.

the cladistic approach seeks in particular to determine the characters specific to a branch, which “sign” a political alliance.
the phenetic approach, a classification only based to measures of distance enters tax (evaluated for example by counting the differences in sequences of DNA) without seeking to make a phylogenetic interpretation.
the probabilistic approach which builds phylogenetic trees by using models of evolution of the characters (generally molecular, but not obligatorily).

According to the publications, one to date finds classifications of any type, since hardly altered traditional classification, until strictly phylogenetic classifications while passing by various mixtures, for example keeping the categories, but aligning oneself on the recent discoveries as regards phylogeny.

Concept of Species

An important concept of classification, rather stable, is that of Espèce. This grouping is relatively well defined, at least for the species with reproduction.

The species is defined as a community of living beings interféconds (or interfertiles , able to reproduce between them), being able to exchange genetic material and producing fertile descendants themselves (indeed, certain individuals of same the kind but pertaining to different species can cross to give an individual Hybride, but this one is generally sterile). In the case of the asexual multiplication strictly , one speaks wrongly about species in the place of line, the grouping being then purely phylogenetic. The case of the entities in extreme cases of alive (Virus, prion S) is still different; they are in general excluded from classifications. Another difficulty of quoting is that of strict symbioses, as the Lichen S (which combine an organization of fungic nature, and an organization capable of photosynthesis, of vegetable nature), but in general, one of the two partners is able to live without joining the other, and one can classify them in two distinct species, with like characteristic of one of the two species being able to survive without the other.

Strictly speaking , the concept of species implicitly supposes a strong Hypothèse which is the transitivity possible interfécondations; in other words, it is supposed that if X1 is interfécond with X2, X2 with X3, etc, X1 will be interfécond with Xn whatever the length of the chain. Konrad Lorenz announces that this assumption is not always true, in particular at marine Oiseaux between continents. It is necessary besides well that this kind of discontinuity exists so that a phenomenon of Spéciation starts to appear him too.

Latin Binomial

The species are named according to the system binominal set up by Carl von Linné. A name of species is the combination of two Latin words (up to three in certain disciplines, for a subspecies, variety or form) generally written in Italiques: a name of kind, follow-up of one or two epithets specific.

Below the row of kind, all the names of let us tax are called combinations. One distinguishes several categories of combinations:

Between kind and species (sub-genus, section, sub-section, series, under-series, etc), the combinations are infrageneric and binominales: name of kind, then after indication of the row, a infrageneric epithet, for example the Cèpe belongs to the section “ Boletus sect. Edules ”;
With the row of species, the combinations are specific and binominales;
Below the species, the combinations are infraspecific and trinominales.

For the details, to see Name binominal and Row taxinomic.

Quotation of authors

When the precision is necessary, one makes follow the binomial of the quotation of authors and the date (the year is enough) of the princeps publication. For example, “ Panthera leo Linnaeus, 1758” indicate the Taxon with the row of species, called in French “lion”, as defined and named by Carl von Linné on this date. See the details on the pages Quotation of authors in botany and Quotation of authors in zoology

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