How does Genetic Variation relate to Selection?

Genetic variation is a measure of the genetic differences that exist within a population. Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population. Genetic variation is caused by: mutation.

Genetic variation is important to the processes of natural selection and biological evolution. The genetic variations that arise in a population happen by chance, but the process of natural selection does not. Natural selection is the result of the interactions between genetic variations in a population and the environment.