Studying the composition of DNA is an important task. The availability of such information makes it possible to identify the characteristic features of all living organisms and study them.
Definition
View is the main form of organization of terrestrial life. It is he who is considered the main unit of classification of biological objects. Those problems that are associated with this term are best analyzed in a historical aspect.
History Pages
The term "species" has been used since ancient times to characterize the names of biological objects. Carl Linnaeus (Swedish naturalist) suggested using this term to characterize the discreteness of biological diversity.
Differences between individuals in terms of the minimum number of external parameters were taken into account when selecting species. This method was called the typological approach. When assigning an individual to a species, its characteristics were compared with the description of those species that were already known.
In those cases where it was not possible to make a comparison according to ready-made diagnoses, a new species was described. In some cases, incidental situations arose: females and males belonging to the same species were described as representatives of different classes.
KBy the end of the 19th century, when there was enough information about mammals and birds living on our planet, the main problems of the typological approach were identified.
In the last century, genetics has developed significantly, so the species began to be considered as a population that has a unique similar gene pool that has a certain “protection system” for its integrity.
It was in the 20th century that the similarity in biochemical parameters became the basis of the concept of species, the author of which was Ernst Mayer. Such a theory detailed the biochemical criterion of species.
Reality and Appearance
Ch. Darwin's book "The Origin of Species" deals with the possibility of mutual transformation of species, the gradual "emergence" of organisms with new features.
A species can be considered a set of ecologically and geographically similar populations that are capable of interbreeding under natural conditions. They have similar biochemical properties, common morphophysical features.
View criteria
They mean the sum of some features inherent in only one species. Each has its own characteristic parameters that need to be analyzed in more detail.
The physiological criterion is the similarity of life processes, for example, reproduction. Interbreeding between members of different species is not expected.
Morphological criterion implies an analogy in the external and internal structure of individuals of the same species.
Biochemical species criterion linked to specificitynucleic acids and proteins.
A genetic trait implies a specific set of chromosomes that differ in structure and complexity.
Ethological criterion is related to habitat. Each species has its own areas of occurrence in the natural environment.
Main Features
View is considered a qualitative stage of wildlife. It can exist as a result of various intraspecific relationships that ensure its evolution and reproduction. Its main feature is a certain stability of the gene pool, which is maintained by the reproductive isolation of some individuals from other similar species.
To maintain unity, free interbreeding between individuals is used, leading to a constant flow of genes within the tribal community.
Each species for several generations adapts to the conditions of a certain area. The biochemical criterion of a species involves a gradual restructuring of its genetic structure, caused by evolutionary mutations, recombinations, and natural selection. Such processes lead to the heterogeneity of the species, its disintegration into races, populations, subspecies.
To achieve genetic isolation, it is necessary to separate related groups by seas, deserts, mountain ranges.
The biochemical criterion of a species is also associated with ecological isolation, which consists in a mismatch in the timing of reproduction, the habitat of animals in different tiers of the biocenosis.
If interspecific crossing occurs or hybrids with weakenedcharacteristics, then this is an indicator of the qualitative isolation of the species, its reality. K. A. Timiryazev believed that a species is a strictly defined category that does not involve modifications, and therefore does not exist in real nature.
Ethological criterion explains the process of evolution in living organisms.
Population
The biochemical criterion of the species, examples of which can be considered for different populations, is of particular importance for the development of the species. Within the range, individuals of the same species are distributed unevenly, since in wildlife there are no identical conditions for reproduction and existence.
For example, mole colonies spread only in certain meadows. There is a natural decay of the population of the species into populations. But such distinctions do not remove the possibility of interbreeding between individuals located in the border areas.
The physiological criterion is also connected with the fact that the population density undergoes significant fluctuations in different seasons and years. A population is a form of existence in certain environmental conditions, it is rightfully considered a unit of evolution.
It can be considered a set of individuals of the same species capable of free interbreeding.
They exist for a long time in some part of the range, to some extent isolated from other populations. What is the biochemical criterion of a species? If individuals of one population have a significant number of similar characters, internalcrossing. Despite this process, populations are characterized by genetic heterogeneity due to the constantly emerging hereditary variability.
Darwinian divergence
How does the theory of divergence of characteristics of the properties of descendants explain the biochemical criterion of the species? Examples of different populations prove the possibility of existence with external homogeneity of a significant number of differences in genetic traits. This is what allows the population to evolve. Survive under harsh natural selection.
View types
Separation is based on two criteria:
- morphological, which involves identifying differences between species;
- reproductive isolation assessing the degree of genetic individuality.
When describing new species, some difficulties often arise, which are associated with the incompleteness and gradualness of the process of speciation, as well as with the ambiguous correspondence of criteria to each other.
The biochemical criterion of species, the definition of which has different interpretations, makes it possible to single out such “types”:
- monotypic is characterized by an unbroken vast range, on which geographical variability is weakly expressed;
- polytypic implies the inclusion of several geographically isolated subspecies at once;
- polymorphic implies the existence within one population of several morpho-groups of individuals thatdiffer significantly in color, but can interbreed. The genetic basis of the phenomenon of polymorphism is quite simple: the differences between morphs are explained by the influence of different alleles of the same gene.
Polymorphism examples
Adaptive polymorphism can be seen on the example of the praying mantis. It is characterized by the existence of brown and green morphs. The first option is difficult to detect on green plants, and the second one is perfectly camouflaged in dry grass, tree branches. When transplanting mantises of this species to a different background, adaptive polymorphism was observed.
Hybridogenic polymorphism will be considered on the example of the Spanish wheatear. Males of this species are in black-throated and white-throated morphs. Depending on the characteristics of the area, this ratio has certain differences. As a result of laboratory studies, a hypothesis was put forward about the formation of the black-throated morph in the process of hybridization with the bald wheatear.
Twin Species
They can live together, but there is no crossing between them, slight morphological differences are observed. The problem of distinguishing similar species is determined by the difficulty of identifying their diagnostic characteristics, since such twin species are well versed in their “taxonomy”.
This phenomenon is typical for those groups of animals that use smell when looking for a partner, for example, rodents, insects. Only in some cases, a similar phenomenon is observed in organisms that use acoustic and visual signaling.
Klesty pine and spruceare an example of sibling species among birds. They are characterized by cohabitation over a large area that covers the Scandinavian Peninsula and Northern Europe. But, despite this, interbreeding is not typical for birds. The main morphological differences between them are in the size of the beak, which is significantly thicker in the pine.
Semi-species
Given that the process of speciation is lengthy and thorny, forms may appear in which it is rather problematic to distinguish the status. They did not become a separate species, but they can be called a semi-species, since there are significant morphological differences between them. Biologists call such forms "borderline cases", "semi-species". In nature, they are quite common. For example, in Central Asia, the common sparrow coexists with the black-breasted sparrow, which is close to it in characteristics, but has a different color.
Despite having one habitat, there is no hybridization between them. In Italy, there is a different form of sparrow, which appeared as a result of the hybridization of the Spanish and brownies. In Spain, they co-exist, but hybrids are considered rare.
In closing
In order to explore the diversity of life, man had to create a certain system of classification of organisms to divide them into separate species. View is the minimum structural unit that has developed historically.
It is characterized as a set of individuals similar in physiological, morphological, biochemical characteristics, giving high-quality offspring,adapted to specific environmental conditions. Such signs allow biologists to keep a clear classification of living organisms.
