Stabilizing selection: the essence and importance of it in human life

As is known from biology, for example, such a relic plant as ginkgo, or such a cystpiper fish, as the coelacanth, exist practically unchanged for about a million years. How can such stability of species be explained in the presence of a permanent mutational process in nature? The answer to this question is given by the consideration of the concept of "stabilizing selection" - a doctrine that was developed by the famous evolutionist II. Schmalhausen.

This type of selection can be observed only in constant conditions of the environment for a sufficiently long time. That is why in an invariable environment, basically, there are typical and perfectly adapted to it individuals, and somewhat different from them mutants must perish. Stabilizing selection is confirmed by a sufficient number of examples. So, after strong winds and snowfalls in North America, about 136 half-dead stunned sparrows were found, only 72 of them survived. Among them were sparrows with medium wings, due to which they possessed greater endurance than those with wings either very long or very short.

Stabilizing selection can lead to phenotypic homogeneity of the population. With its long-term impact on the environment, it may appear that the species or population is unchanged. However, this immutability is only apparent and can concern only appearance. In this case, the gene pool undergoes certain changes (a mutation takes place).

Stabilizing selection is also characteristic of man. An example is Down's syndrome. After all, it is known that violations of small 21-22 pairs of chromosomes lead to this hereditary disease. In case of deviations in the number and shape of large chromosomes, the death of fertilized eggs occurs. Also spontaneous abortions are often caused by the death of embryos with deviations in the middle chromosomes.

Stabilizing selection for several hundred thousand generations is responsible for the conservation of species from significant changes, rejecting the promutizing forms. Without it, some stability in living nature would not have been achieved.

Along with the already considered stabilization, there is still an individual selection, which is advisable to consider the example of plants. Its main essence is to determine the quality of selected plants with the help of an individual evaluation of their offspring. In contrast to mass selection, individual seeds of selected plants are not mixed, but are sown by families separately in separate areas in order to obtain a qualitative assessment of their offspring. Thanks to this approach, it is possible to obtain a selection by genotype, and not by phenotype.

Unconscious selection is more applicable to man, and is performed without a specific pre-set task. Thus, Darwin proved that, for example, if a peasant has two cows on the farm, he will kill the meat that gives the less milk, and the hens will use bad layers for the meat. In one and the second case, the peasant, in an effort to preserve productive animals, makes a selection without setting himself the goal of breeding new breeds. It is in this somewhat primitive form that Darwin shows unconscious selection.

Studying the life of the peoples of Australia and South Africa, the scientist more and more convinced of the correctness of his judgments. Unconscious selection for a long time was done by a person when taming wild animals. This is what served as the formulation of an important conclusion that in agriculture new species of animals and plants can be obtained only through selection. Thus, from the doctrine of unconscious selection of Darwin, "another", no less important, doctrine of artificial selection "emerges" , which is formulated in the form of a law that subordinates to itself the entire process of breeding new varieties of plants and animal breeds.