The variety in a species comes through in DNA. When a new and helpful mutation arises, it will help individuals in the species to better . Over the following generations, the new trait will become more prominent in a population (or even essential) since it increases the chances of . (For example, the first bats to fly would have had an advantage over other bats who did not have the new genes necessary. The flight gene likely quickly during the following generations since it is so useful for survival.)