What is the result of variability, natural selection?

The variability of organisms is of two types: a change in the genotype and a change in the phenotype. In the first case, the changes that have occurred can be passed on to the offspring, and in the second, such a transfer is excluded.
Variability is classified into mutation, modification, and combination.
Mutation occurs as a result of exposure to ultraviolet rays, radiation on the body, which can change deoxyribonucleic acid.
During sexual reproduction, a combination of the genes of the parents occurs, which also affects the future offspring.
Modification changes occur as a result of the impact of the environment on the organism, but this does not change its genotype.