The morphological criterion of the form

In the process of practical human activity, the notion of a species evolved. Aristotle applied this concept to the description of animals. However, for quite a long period, the definition of "species" was not endowed with scientific content and was used as a logical term. The status of the unit of classification the concept in question has acquired in the development of systematics. John Ray (English naturalist) has developed an idea of the form as a component of taxonomy. At the same time three important characteristics of this unit were singled out to scientists. Thus, in the opinion of Rhea, the species is a set of organisms, for which a common origin is characteristic. This systematic unit combines organisms similar in morphological and physiological characteristics. In addition, it is a self-reproducing system.

The origin of Rey considered the main indicator. For example, a naturalist referred to similar plants, reproducing from their seeds to themselves.

A significant extension of the concept of the species, as well as its deepening, was due to the work of Linnaeus, who showed that the species is a real elementary and stable unit of living nature, detached from other species. This concept was used as the main classification of animals and plants. However, in those days the species was viewed as a consequence of creative action.

Lamarck proclaimed in his writings the thesis that in nature there are no fixed systematic units of plants and animals. The species are constantly changing, changing, changing into other species. In this regard, according to Lamarck, the old systematic unit can not be separated from the new one. Thus, the French naturalist came to the conclusion about denying the reality of the species, while affirming the idea of development.

Darwin's doctrine was based on a different situation. This provision was scientifically justified. In accordance with it, the developing real species is conditioned by historical development under the influence of natural selection. In accordance with the Darwinian doctrine, a comprehensive study of systematic units was carried out. Thus, the study of the morphological criterion of the species, as well as an experimental, genetic study of the structure and ways of its formation were carried out. These measures were of decisive importance in justifying the population aspect of the systematic unit as the main form of development and existence of the organic world as a whole.

Today it is believed that the organic environment includes a variety of life forms. In this case, the "species" is a universal phenomenon for the whole living nature. The considered systematic unit is formed in the course of evolutionary transformations, conditioned by natural selection. As a result, it represents a concrete stage (link) of the development of living organisms and is the main form of existence on the planet of life.

One species differs from the other in a set of common features - criteria. In a complex these attributes form the reality of systematic units.

Morphological criteria of the species are based on the presence in all individuals of one species of certain hereditary traits. Individuals within a single systematic unit, in other words, have a similar external and internal structure. The morphological criterion of a species is considered quite convenient and a simple sign. Moreover, this characteristic was applied by taxonomists earlier than other characteristics and for a certain period was the main one. However, it should be noted that the morphological criterion of the species is rather relative. This sign is necessary, but insufficient. The morphological criterion of the species does not allow us to distinguish between systematic units having a significant similarity in structure, but not interbreeding with each other. For example, systematic units are twins. So, the name "malarial mosquito" includes about fifteen species, indistinguishable externally, but previously considered one species. It is established that about 5% of all systematic units are twins. Thus, the morphological criterion of a species can not be the only sign of difference.