We tend to think of mutations as something negative or harmful; the term “mutant” ordinarily connotes something abnormal. But because mutations result in genetic variation among individuals and organisms, we are all mutants, different from one another genetically because of mutations, that is, differences in our DNA. Whereas some mutations are harmful, some have no effect on an organism, and some indeed are beneficial. Without mutations, evolution would not be possible. Mutations generate the occasional favorable variants that allow organisms to evolve and become adapted to their environment over time (Chapter 21).