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It is defined as the process through which evolutionary changes in living organisms occur over time. It mostly affects the organism's survival and reproductive success.

It is highly adapted to the environment, resulting in the persistence of genetic features that are well suited to that environment.

In comparison to organisms that are less adapted to that habitat, survivors who stay in the environment tend to generate more offspring. As a result, the qualities and characteristics of populations vary throughout time.

The directed sectional is an example presented in the question, in which the phenotype is chosen at one end of the existing variation spectrum. The moth was discovered to be light in color before the industrial revolution, allowing it to blend in with light colored trees and lichens.

Following the establishment of factories, the trees darken, making light-colored moths easier to spot. Because of their high survival rate, the moths' color fades with time. They merged in with the sooty trees due to their deeper tint. Because industries have been cleaner in recent years and less soot is emitted into the atmosphere, the moth has switched to a lighter hue.