Final answer:
The balance between mutation and selection explains the persistence of traits within populations. Mutations introduce genetic variation, while selection acts on this variation, favoring traits that increase relative fitness in a given environment.
Step-by-step explanation:
The balance between mutation and selection explains the persistence of genetic diversity and specific traits within a population. Mutations are random changes to an organism's DNA, which can result in new traits. These mutations are one of the main sources of genetic variation among individuals. Whether a mutation is beneficial or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. On the other hand, selection (including natural selection and sexual selection) acts on this genetic variation, preferentially amplifying certain traits that increase an individual's relative fitness within the environment they live in.
For instance, light-colored mice living on a beach may be well-camouflaged in the sand, while dark-colored mice blend in with grass patches. An intermediate, medium-colored coat would be disadvantageous since it provides neither camouflage advantage, making those mice more susceptible to predation. Therefore, disruptive selection may maintain both light and dark-colored individuals within the population because stabilizing selection for an intermediate coat color would be maladaptive.