In the course of practical human activity evolved the concept of form.In describing the animal has already applied this concept by Aristotle.However, a sufficiently long period, the definition of "species" were not endowed with scientific content and is used as a logical term.The status of the unit, consider the notion acquired in the development of taxonomy.John Ray (English naturalist) developed the idea of the form as a component of systematics.At the same time the scientists had identified three major characteristics of this unit.So, look, according to Ray, is a variety of organisms, which are characterized by a common origin.This systematic unit combines similar morphological and physiological characteristics of the organism.In addition, she is a self-playing system.
Origin Rey considered the main indicator.For example, one type of naturalist attributed similar plants reproduce from seeds of its own kind.
significant expansion of the species concept and its deepening happen through the work of
Lamarck declared in his writings about the situation is that in nature there is no invariable taxonomic units of plants and animals.Forms are constantly transformed, changed, transformed into other types.In this regard, according to Lamarck old systematic unit can not be separated from the new.Thus, the French naturalist concluded that the denial of the reality of the species, arguing that the idea of development.
Darwinian doctrine was based on a different position.This has been scientifically proved.In accordance with this kind of real-paced due to the historical development under the influence of natural selection.In accordance with the teachings of Darwin carried out a comprehensive study of systematic units.Thus, the study was conducted morphological criteria species, as well as experimental, genetic study of the structure and the ways of its formation.These activities have been crucial in justifying the systematic aspects of population units as the main form of development and existence of the organic world as a whole.
Today, it is believed that the organic medium includes a variety of life forms.This "look" is a universal phenomenon in all of nature.Examine systemic unit is formed in the course of evolutionary changes caused by natural selection.As a result, it represents a concrete step (link) the development of living organisms and is the main form of existence of life on the planet.
one species differs from another set of common characteristics - criteria.Together, these attributes form the reality of systematic units.
morphological criteria based on the type of presence in all individuals of a species specific hereditary characteristics.Individuals within the same taxonomic units, in other words, have similar internal and external structure.Morphological criteria of the type considered sufficiently convenient and simple sign.Moreover, this characteristic was used earlier taxonomists and other features for a specific period is essential.However, it should be noted that the morphological criteria of the form rather relative.This feature is a necessary but not sufficient.Morphological criteria distinguish between species does not allow systematic units having a substantial similarity in structure, but do not interbreed with each other.For example, the systematic unit-doubles.Thus, the name "anopheles" includes about fifteen species indistinguishable in appearance, but previously considered a single species.It was found that about 5% of all taxonomic units are doubles.Thus, the morphological criteria of the form can not be the only sign of distinction.