Answer:
mutations
Step-by-step explanation:
Mutations are changes in DNA sequence that can create genetic variation within the population and thus are the ultimate source of new alleles . Mutations are important for evolution because of their ability to form a new genetic variant (allele) that can be spread to the offspring. If a new variant of a trait formed by a mutation is advantageous and helps the organism to survive and reproduce, it is going to be favourable by natural selection. That variation will more likely be passed to the next generation and remain over time.