Mutations Cause DNA Code to Be Changed in Passing From Parent to Offspring. Well Adapted Than Parents. Mutation Tends to Die out. If Mutation Is Minor, Has Little Immediate Effect on Offspring. Mutation Doesn't Die Out, But Is Passed On.
Most Organisms are already Well-Adapted, so any change is likely to be harmful.
Mutations rarely have any immediate effect. If conditions change, then the mutation may be better for the organism, and those organisms without the mutation may die out.