Answer:
Natural Selection
Step-by-step explanation:
Genetic variations are one of the most important factors in the evolution of organisms. Mutations are fundamental in this process. When a mutation is produced in an organism, and that mutation produces an 'attractive' trait that will potentially help the organism to reproduce, then, this trait (if the mutation is hereditary) will be passed on to the subsequent generations and will stay in the population as it is beneficial.
This perfectly illustrates natural selection, which refers to a process in which a trait that is advantageous will stay in a given species if it helps the individual to survive and reproduce. In other words, nature "selects" the organisms that possess the 'best' traits so they can pass them from generation to generation and increase their chances of survival.