What is the ability of a population to adapt (adapt) to new conditions?

Since every population is usually well adapted to its habitat, large changes usually reduce this fitness, just as significant random changes in the watch mechanism (removing some spring or adding a wheel) lead to a malfunction in their work. In populations, there are large stocks of such alleles that do not bring her any benefit in a given place or at a given time; they remain in the population in a heterozygous state until, as a result of changes in environmental conditions, they are suddenly useful. As soon as this happens, their frequency under the influence of selection begins to increase, and ultimately they become the main genetic material. This is where the ability of the population to adapt, that is, to adapt to new factors – climate change, the emergence of a new predator or competitor, and even human pollution.
An example of such adaptation is the evolution of insect species that are resistant to insecticides. Events in all cases develop in the same way: when a new insecticide (poison acting on insects) is introduced into practice, a small amount of it is enough to successfully combat a pest insect. Over time, the concentration of the insecticide has to be increased until, finally, it is not effective. The first report on insect resistance to an insecticide appeared in 1947 and related to the resistance of a housefly to DDT. Subsequently, resistance to one or more insecticides was found in no less than 225 species of insects and other arthropods. Genes capable of providing insecticide resistance were obviously present in each of the populations of these species; their action and ultimately ensured a decrease in the effectiveness of poisons used to control pests