What is a mutation? At first, it may sound like a bad thing, and sometimes it is. However, life as we know it today could not exist without mutations. They are the reason that organisms have changed over the course of time. What does this mean? Mutations generate the raw material for natural selection and are the main source for genetic variation in the gene pool. Mutations can be harmful, beneficial, or neutral (meaning they have no effect on the organism in which the mutation occurs). Let’s look at mutations, how they occur, and how they contribute to genetic variation.