How DNA evolves

Occasionally, there are small errors, or “mutations”, in the copying process and the DNA code is altered slightly. Mutations are the ultimate source of variation and novelty in evolution and we all carry mutations that make us different from our parents. The vast majority of mutations are harmless; in fact, some are good! When the child grows up and eventually has children of his or her own, these mutations will be present in the DNA passed on to the offspring. In this way, mutations are preserved in the genetic code passed on from generation to generation. Over time, these tiny changes accumulate so that one family line develops a unique genetic code that distinguishes that lineage from all others.