Practica De Biologia

Biological classification, or scientific classification in biology, is a method of scientific taxonomy used to group and categorize organisms hierarchically. Rank-based systems use a fixed number of levels in the hierarchy, such as kingdom, family, genus or species. Rankless systems use an arbitrary number of levels. The groups in the classification are known as taxa (singular: taxon).

Modern biological classification has its root in the work of Carolus Linnaeus, who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent.

With the introduction of the cladistic method in the early 20th century, formalized by Willi Hennig in the mid-20th century, phylogenetic taxonomy in which organisms are grouped purely on inferred evolutionary relatedness (based either on classical evidence of morphology, chemistry, physiology, ecology or molecular evidence or both) has become common in biology.[1] Molecular phylogenetics, which uses DNA sequences as data, has driven many recent revisions and is likely to continue doing so. Biological classification belongs to the science of systematics.

Contents [hide]

1 Definition

2 Biological types

3 Taxonomic ranks

4 Early systems

4.1 Ancient through medieval times

4.2 Renaissance through Age of Reason

4.3 Early methodists

4.4 Linnaean taxonomy

5 Modern system

5.1 Kingdoms and domains

6 Authorities (author citation)

7 Globally unique identifiers for names

8 See also

9 References

10 Bibliography

Definition[edit]

Biological classification has been defined by Ernst Mayr as "The arrangement of entities in a hierarchical series of nested classes, in which similar or related classes at one hierarchical level are combined comprehensively into more inclusive classes at the next higher level." A class is defined as "a collection of similar entities".[2] (Note that the word "class" is used quite separately for one of the levels in the biological hierarchy.)

Biological classification is based on shared descent from their nearest common ancestor. Accordingly, the important attributes or traits for biological classification are 'homologous', i.e., inherited from common ancestors.[3] These must be separated from traits that are analogous. Thus birds and bats both have the power of flight, but this similarity is not used to classify them into a taxon (a "class"), because it is not inherited from a common ancestor. In spite of all the other differences between them, the fact that bats and whales both feed their young on milk is one of the features used to classify both of them as mammals, since it was inherited from a common ancestor(s).

Determining whether similarities are homologous or analogous can be difficult. Thus until recently, golden moles, found in South Africa, were placed in the same taxon (insectivores) as Northern Hemisphere moles, on the basis of morphological and behavioural similarities. However, molecular analysis has shown that they are not closely related, so that their similarities must be due to convergent evolution and not to shared descent, and so should not be used to place them in the same taxon.[4]

Biological types[edit]

Main article: Type (biology)

The scientific names of taxa are formally attached to a type, which is one particular specimen (or in some cases a group of specimens, or in some cases an illustration) of the organism, preserved in a museum. The type is the example that serves to anchor or centralize the defining features of each particular taxon.

Taxonomic ranks[edit]

Main article: Taxonomic rank

A classification

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