Systematics of organisms
Systematics of organisms, biological systematics - the oldest field of biological sciences, the science of classifying, cataloging and describing organisms based on the study of their diversity, origin and relatedness. Systematics groups organisms into units that are taxa in the hierarchical structure of systematic categories, resulting in a systematic system (system). The rules of classification and systematic nomenclature are determined by taxonomy, and the relationships of evolutionary kinship between taxa - by phylogenetics. Sometimes the term "taxonomy" is extended to cover the whole taxonomy, but in the strict sense it is its section dealing with the methodological, mathematized side. So far, at least 1.75 million species of organisms currently living on Earth and several hundred thousand extinct organisms have been discovered, described and named.
An outline of the history of taxonomy
The oldest attempts at scientific systematization of plants and animals are known from antiquity. The first systematic system of animals, based on the external properties of the structure, was created by Aristotle, and his student and friend Theophrastus of Eresus formulated the differences between the animal and plant worlds and introduced the division of the plant world into 4 groups, maintained until the 16th century. Carl Linnaeus had a significant influence on the development of the systematics of organisms, who described about 10 thousand. plant species and about 6,000 animal species, and popularized the binomial nomenclature of species.
The original attempts to classify organisms relied on artificially selected criteria, usually external morphological or habitat features. This approach functioned until the nineteenth century. Contemporary systematics aims to organize the information collected about individual organisms, to give each of them a unique name and place them in hierarchically systematized systematic categories, in order to establish a systematic system based on the knowledge of relationships.
In the modern systematics of organisms, three basic research methods can be distinguished:
Genealogical systematics, classical evolutionary systematics - is based on simultaneous anatomical comparative, embryological and palaeontological analysis and on four basic criteria: morphological discontinuity, adaptive niche, species richness and monophiletism (in a broader sense).
Phenetic (numerical) systematics - assumes that it is impossible to know phylogeny and groups taxa with the most common features, similar to the oldest systems, starting with Aristotle. Unlike traditional systematics, however, orthodox phenetics rejects the intuitive ranking of features as more or less important in determining systematic distance.
Phylogenetic systematics - as taxonomic units, it defines clades, i.e. natural groups of organisms including the ancestral species and all descendant species.
Units, Categories, Systems
The basic taxonomic unit is the taxon. Related taxa are grouped into higher level taxa.
In the traditional systematics of organisms, taxa are assigned a rank, referred to as a systematic category.
The current state of knowledge about organisms in a given period is illustrated by taxonomists in the form of a systematic system, called a taxonomic system, systematic classification, biological classification or systematic division of organisms. As the state of this knowledge is constantly changing, new groups of organisms are discovered and research methods are improved - the biological classifications proposed by individual authors are constantly subject to modifications.
In the cladistic systematics, the definition of systematic categories is abandoned, and the phylogenetic relationships between individual taxa are defined by means of clades