Phylogenetic classification

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The phylogenetic classification is a system of classification Systématique of the living beings. It tries to replace the scientific Classification traditional based on multiple features: biological, phenotypical (anatomical) and physiological (physicochemical phenomena, nutrition). One of the characteristics of the phylogenetic approach is that this classification upsets classifications creationists like that developed by Carl von Linné. The binomial nomenclature of Linné was based on the proverb that all the species appeared at the same time and that those were fixed. Whereas phylogenetic classification illustrates the principles of evolutions and relationship of the species.

Presentation

Willi Hennig is at the origin of phylogenetic classification in 1950, it revolutionized thereafter, after the translation in English of its work, all the Systématique starting from the end of the Années 1960. The anatomical characters of the living beings then were analyzed differently, joined soon by the molecular characters. Phylogenetic classification is a system of classification of the living beings initially founded on what the living beings have (at the morphological level as at the molecular level), and not, in first authority, on what they do not have (one will avoid then “invertebrate”) or on what they make (one will avoid then “viviparous”, “digger”). It is not an ecological classification nor anthropocentric. It gathers the living beings on a particular type of resemblance, those of the resemblances which are évolutivement innovating within the sample of species to classify. She is opposed in that to classifications Phénétique S which do not sort the resemblance and make classifications starting from the total resemblance. She replaces the traditional classification based on a crowd of criteria, morphological but so ecological, ethologic, anthropocentric, and preferences nutritional.

Phylogenetic classification validates only groups Monophylétique S, whatever the characters used, molecular, morphological, anatomical, caryologic, genomic. The characters used to build a Phylogenetic tree are valid only if those are characters Apomorphe S shared by at least two Taxon S. (a character apomorphe is an ancestral character which was transformed. This character apomorphe divided is a Synapomorphie. Only the synapomorphies (or characters derived) characterize a Clade or groups monophyletic. A group Monophylétique (or clade) is a group including/understanding an ancestor (or node) and all his descendants.

The first hierarchy is thus made up of three fields:

  1. Archée S
  2. Bacterium S
  3. Eucaryote S

To know which of these three groups divide a common ancestor which distinguishes them from the third is a subject of research.

Systematic the phylogenetic in its modern version rejects any categorization of the hierarchical levels. For practical reasons, the Arbre of alive the gives itself the hierarchy which the old categories tried to provide. The tree of alive is, indeed, a whole of branchpoints. Each level is compared to a Taxon. A taxon is a regrouping of organization defined by a whole of synapomorphies. The points or nodes are obligatorily a theoretical organization which would have the synapomorphies posterior nodes in the cladogramme. If this organization is discovered (fossils or others) a new tree must be built. In the long term, if the tree restores the totality of the relations of relationship, all the connections should be binary. The direction of the dichotomies has nothing to do with sexuality nor with binary speciations, because the tree is not a genealogy (" who goes down from qui"), but reflects only one explanatory capacity maximum of the tree: a completely dichotomic tree succeeds in restoring all the relations of relationship (" who is closer to qui").

The systematic modern one takes into account all the characters héritables, since what is visible (anatomy and morphology, base traditional classification) until the sequences of DNA and ARN, while passing by the Protéine S and the data of the Paléontologie. The sequencing of certain parts of the Genome, like DNA of the Mitochondries or ARN of the Ribosomes made it possible in the last years to make important progress in classification and to solve many secular problems.

The tree is obtained starting from many criteria and is called upon complex algorithms. Different algorithms can give different results. In this case, that which will answer more the criteria of parsimonies will be retained. I.e. the tree asking for the minimum of transformation of characters. Current classification is continuously altered according to new information. The site treebase refers. The examples which follow can have to be modified.

Example of the Man

A detailed example makes it possible to have an idea of the difference in result, compared to the traditional approach. The example impossible to circumvent is that of the Man. Here part of the successive nodes allowing to classify the man (certain intermediaries were omitted arbitrarily) such as appearing in phylogenetic Classification of alive the (Guillaume Lecointre and Herve Guyader, Belin edition) (description associated with each clade is not very rigorous and just aims at fixing the ideas):

  • Species Homo sapiens

  • Kind Homo : includes the fossil species like Néanderthal or erectus
  • Hominines: the kinds Australopithecus and Homo
  • Homininés: two species of chimpanzees and the hominines
  • Family Hominides: gorilla and Homininés
  • Hominoïdés: one adds the orang-outang
  • Hominoïdes: one adds gibbons them
  • Catarrhiniens: monkeys of the old world
  • Simiiformes: Monkey S
  • Haplorrhiniens: monkeys and Tarsier S
  • Order Primate S ( strictly speaking ): most of the old order of the primates
  • Primate S ( lato sensu ): the Scandentiens (toupayes) are added
  • Archontes: are added the Chiroptère S (bat) and the Dermoptère S
  • Preptothériens: are added the majority of the placental mammals
  • Euthériens: the pangolins and fourmiliers (Xénarthres) are added to supplement the placental mammals
  • Thériens: the marsupials
  • Classe Mammifère S are added: the old class of the same name, precedents plus the Monotrème S (ornithorhynques and echidnas)
  • Amniote S: the old class of the reptiles and the birds
  • Tétrapode S are added: approximately the Amphibians
  • Sarcoptérygien S are added: are added Dipneuste S then Coelacanthe S
  • Ostéichthyen S: the actinoptérygiens are added (the major part of “osseous fish”)
  • Vertébré S : the Requin S then the Lamproie S
  • Craniates are added: the Myxine S
  • Embranchement Chordé S are added: amphioxus and ascidies
  • Deutérostomien S are added: Echinodermata are added (starfishes, sea urchins,…)
  • Bilatériens : symmetrical animals: are added to the precedents, inter alia, the protostomiens which include, between many others, various groups of worms, the arthropods (insects), the molluscs (snails)
  • Eumétazoaires: organized animals, are added to the precedents the cnidaires for example
  • Métazoaires: the old animal kingdom, are added to the precedents various groups of sponges

  • Opisthocontes : are added, inter alia, the mushrooms

  • Domaine Eucaryote S: living beings with cells with core; are added to the precedents listed above the green line (green algas, red algas, plants with flowers), the brown line (brown algas,…) and a whole collection of unicellular groupings of species

Differences with traditional classification

Let us quote finally some examples of spectacular changes compared to the traditional classification.

  • All the ancestors of the Dinosaure S are also ancestors of the Oiseau X, which brings to regard those as the descendants of a group of small alive flying dinosaurs to the Crétacé. The concept of “Reptile” is abandoned.
Let us specify the relation between birds and dinosaurs. For certain authors, the Vélociraptor is regarded as nearer to the birds than the Tyrannosaure, and this last is considered nearer to the birds than Diplodocus.
  • more the close relatives of the Cétacé S would be the Hippopotame S. the concept of “Artiodactyle S” is abandoned.
  • more the alive close relatives of the birds are the Crocodile S.
  • the Poisson S osseous are closer to the mammals than Requin S. the concept of “fish” is abandoned.
  • the old group of the “Algue S” explodes in all directions, some being grouped with the house plants, others with the Bactérie S.
  • the concept of “Protiste” is abandoned, with the profit of groups which can mix multicellular beings and monocellulaires (for example the Straménopile S gather the brown Algue S - of which the Kelp, up to 60 m of length - and the unicellular Diatomée S).
  • Procaryotic division between S and Eucaryote S is abandoned, with the profit of division into three of the alive one.
  • the application of this classification to the Angiosperme S is illustrated by the Classification APG (Angiosperms Phylogeny Group).

With reading

See too

External bonds

  • Tree of the life

  • svt 44
  • Treebase
  • Project Tree off Life

Simple: Domain (biology)

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