Natural selection is always the main factor in the transformation of living organisms. It operates according to one mechanism - the strongest survive and leave behind offspring, i.e. the fittest individuals. However, depending on its effectiveness, direction, characteristics of the conditions for the existence of organisms, the forms of natural selection may be different. So, one of its forms is driving selection (directed), which is a response to changes in the environment and contributes to a shift in the average value of a trait or property. For quantitative traits, the average value is equal to the arithmetic mean, for example, the average number of offspring born. And to describe the qualitative properties, the frequency (percentage) of individuals with the necessary trait is determined, for example, the frequency of horned and polled cows.
Analysis of these properties allows you to judge the changes,that appeared in the population in connection with adaptation to changed living conditions. At the same time, motive selection can contribute both to strengthening and weakening of the changed properties of the organism. The so-called industrial melanism can serve as an example of the strengthening of a trait. The type of moth butterfly in non-industrial areas has a light color of the scales covering the body and wings, and in areas with a large number of plants and factories, their color changes to black. The appearance of moths of a color unusual for them is due to the fact that harmful industrial emissions led to the death of lichens that lived on the bark of trees and served as a place for butterflies to settle (protective color). The change in color of the scales increased the butterflies' chance of survival. In this case, the so-called selection criteria worked - the preservation and distribution of a new species of butterflies, which, under changed conditions, are able to continue the genus, i.e. give offspring.
An example of a weakening of a sign is the loss or reduction of an organ and its part in the
due to the fact that it does not carry a functional load - the wings of an ostrich (does not fly), the absence of limbs in snakes.
Propulsive selection is the basis of artificial selection. At the same time, a person, choosing individuals according to certain parameters (phenotype), increases the frequency of this property. It has been empirically proven that such selection for external characteristics leads to some changes in the genotype, and, possibly, the loss of some alleles.
There are such forms of artificialselection - unconscious and methodical. When using unconscious selection, a person, as it were, selects the best on an intuitive level. The result of such a sample is the emergence of new breeds and varieties characteristic of a particular area. The methodical principle is used in breeding to obtain new species of plants and animals adapted to certain conditions of growth and residence (frost-resistant species of ratsenia).
Thus, motive selection is a form of natural selection, the result of which is the emergence of a new, adapted species of organisms that can survive and procreate in changing environmental conditions.
