Natural selection is a process by which organisms that are most suited to their environment survive and reproduce most successfully; also called survival of the fittest.
Natural Selection occurs in any situation in which more individuals are born than can survive, there is natural heritable variation, and there is variable fitness among individuals.
It occurs through adaptation because it is heritable characteristic that increases an organism's ability to survive and reproduce in an environment
It occurs through fitness because it is how well an organism can survive and reproduce in its environment
Evidence of Evolution
Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors