Studying the composition of DNA is an important task. The presence of such information allows us to identify the characteristic signs of all living organisms, to study them.
Definition
View is the main form of organization of earthly life. It is he who is considered the main unit of classification of biological objects. Those problems associated with this term are best analyzed in the historical aspect.
Pages of history
The term “species” has been used since ancient times to describe the names of biological objects. Karl Linney (Swedish naturalist) suggested using this term to characterize the discreteness of biological diversity.
When isolating species, differences between individuals by the minimum number of external parameters were taken into account. This method has been called the typological approach. When classifying an individual as a species, its characters were compared with a description of those species that were already known.
In those cases when it was not possible to compare the prepared 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.
By the end of the 19th century, when there was already enough information about mammals and birds living on our planet, the main problems of the typological approach were identified.
In the last century, genetics received significant development, so the species began to be considered as a population with a unique similar gene pool, which has a certain “protection system” for its integrity.
It was in the 20th century that similarity in biochemical parameters became the basis of the concept of the species, the author of which was Ernst Mayer. A similar theory described in detail the biochemical criterion of the species.
Reality and view
In the book of C. Darwin, “The Origin of Species,” we are talking about the possibility of the mutual transformation of species, the gradual “nucleation” of organisms with new traits.
The 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 characteristics.
View criteria
They mean the sum of some features inherent in only one species. Each has its own characteristic parameters that need to be disassembled in more detail.
The physiological criterion is the similarity of vital processes, for example, reproduction. Crossing between representatives of different species is not supposed.
The morphological criterion assumes an analogy in the external and internal structure of individuals of the same species.
The biochemical criterion for the species is related to the specificity of nucleic acids and proteins.
A genetic trait suggests a specific set of chromosomes that differ in structure and complexity.
The ethological criterion is associated with the habitat. Each species has its own areas of presence in the natural environment.
Main features
The species is considered a quality step in 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 supported by the reproductive isolation of some individuals from other similar species.
To maintain unity, free crossing 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 particular area. The biochemical criterion of a species involves a gradual restructuring of its genetic structure caused by evolutionary mutations, recombinations, and natural selection. Similar processes lead to heterogeneity of a species, its decay into races, populations, subspecies.
To achieve genetic isolation, it is necessary to separate related groups by the seas, deserts, mountain ranges.
The biochemical criterion of the species is also associated with environmental isolation, which consists in a mismatch in the breeding dates, and the habitat of animals in different tiers of the biocenosis.
If interspecific crossing occurs or hybrids with weakened characteristics appear, 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.
The ethological criterion explains the process of evolution in living organisms.
Population
The biochemical criterion of a 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 one species are distributed unevenly, since in living nature there are no identical conditions for reproduction and existence.
For example, mole colonies are distributed only in individual meadows. There is a natural decay of the population of the species into populations. But such distinctions do not remove the possibility of crossing between individuals located on border areas.
The physiological criterion is also associated with the fact that population density undergoes significant fluctuations in different seasons and years. A population is a form of existence under certain environmental conditions; it is rightly considered a unit of evolution.
It can be considered a collection of individuals of the same species, capable of free crossbreeding.
They exist over a long time period in some part of the range, to some extent isolated from other populations. What is the biochemical criterion of the species? If individuals of one population have a significant number of similar characteristics, internal crossbreeding is allowed. Despite a similar process, populations are characterized by genetic heterogeneity due to constantly appearing hereditary variability.
Darwin divergence
How does the theory of the divergence of traits of the properties of the descendants explain the biochemical criterion of the species? Examples of different populations prove the possibility of a significant number of differences in genetic traits with external uniformity. This is what enables the population to evolve. Survive in tough natural selection.
Types of species
Separation is based on two criteria:
- morphological, which involves the identification of differences between species;
- reproductive isolation assessing the degree of genetic identity.
When describing new species, some difficulties often arise that are associated with the incompleteness and gradualness of the process of speciation, as well as with the ambiguous correspondence of the criteria to each other.
The biochemical criterion of a species, the definition of which has different interpretations, allows us to distinguish such "types":
- monotypic is distinguished by an unbroken vast area on which geographical variability is weakly expressed;
- polytypic implies the inclusion of several subspecies isolated geographically;
- polymorphic implies the existence within the same population of several morpho-groups of individuals that differ 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 effect of different alleles of the same gene.
Examples of polymorphism
Adaptation polymorphism can be seen in the example of a mantis. It is characterized by the existence of a brown and green morph. The first option is difficult to detect on green plants, and the second is perfectly masked in dry grass, tree branches. When transplanting mantis of this species to a different background, adaptive polymorphism was observed.
Hybrid polymorphism we consider on the example of the Spanish Kamenka. Males of this species in black-necked and white-necked morphs. Depending on the characteristics of the range, this ratio has certain differences. As a result of laboratory studies, a hypothesis was put forward on the formation of a black-necked morph in the process of hybridization with a bald-headed stone.
Double species
They can live together, but there is no crossing between them, weak morphological differences are observed. The problem of differences between similar species is determined by the complexity of identifying their diagnostic characteristics, since such twin species are well versed in their “taxonomy”.
A similar phenomenon is characteristic of those groups of animals that use the smell, for example, rodents, insects, when searching for a partner. Only in some cases a similar phenomenon is observed in organisms that use acoustic and visual signaling.
Crossbills pine and spruce are examples of twin species among birds. They are characterized by cohabitation on a large territory that covers the Scandinavian Peninsula and Northern Europe. But, despite this, birds are not characterized by interbreeding. The main morphological differences between them are in the size of the beak; it is significantly thicker in the pine tree.
Half-species
Considering that the process of speciation is long and thorny, forms may appear in which it is rather problematic to single out 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 found quite often. For example, in Central Asia, the common sparrow coexists with the black-chested sparrow, which is similar in characteristics to it, but has a different color.
Despite 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 Spanish and brownie. In Spain, they exist together, but hybrids are considered rare.
Finally
In order to explore the diversity of life, a person had to create a certain system of classification of organisms to subdivide them into separate species. A view is a minimal structural unit that has developed historically.
It is characterized as a collection of individuals similar in physiological, morphological, biochemical characteristics, giving high-quality offspring adapted to specific environmental conditions. Such signs allow biologists to clearly classify living organisms.