Final answer:
Natural selection is a major mechanism of evolution. It acts on existing variations in a population, selecting individuals with traits that are better adapted to their environment.
Step-by-step explanation:
Natural selection is a major mechanism of evolution. It acts on existing variations in a population, selecting individuals with traits that are better adapted to their environment. This process leads to the survival and reproduction of individuals with advantageous traits, resulting in the evolution of populations over time. However, natural selection does not create new traits; it works with the genetic variation that already exists within a population.