Here's why:
* Mutations are changes in the DNA sequence. These changes can be small (a single nucleotide change) or large (deletions, insertions, rearrangements).
* Mutations introduce new alleles (versions of genes) into a population. This increases the diversity of traits within a population.
* Natural selection acts on this existing variation. Individuals with traits better suited to their environment are more likely to survive and reproduce, passing on their beneficial alleles.
* Over time, this process of mutation and natural selection can lead to significant evolutionary change.
It's important to note that other factors like gene flow (migration) and sexual reproduction can also contribute to genetic variation, but they don't introduce *new* alleles like mutations do.
