Natural selection is the process through which populations of living organisms adapt and adjust. Individuals in a population are distinct in some ways making them naturally variable. This means that some individuals have traits better fitted to the environment than others.
Genetic variation refers to differences among the genomes of members of the same species. Genetic variation within a species can result from a few different sources. Gene variation that change gene activity or protein function can offer various traits in an organism. If a trait is advantageous and benefits the individual to endure and recreate, the genetic variation is more likely to be passed to the next generation.