When a wound does not heal properly, it leaves a scar. Similarly, mutations—which are permanent changes to genetic code—are often the result of damaged DNA that has not been properly repaired. Mutations can impede the function of genes and lead to disease and aging, but they are also the source of genetic variation, which allows new traits to emerge and facilitates the evolutionary process. Scientists still do not fully understand why some damaged DNA segments are successfully repaired while others are not. ...read more read less