Final answer:
Natural selection is the process where organisms best adapted to their environment survive and reproduce, leading to the prevalence of beneficial traits within a species. Genetic variation is key to this process, and adaptations occur as a result, such as the beak shapes of Galapagos finches.
Step-by-step explanation:
Natural selection is a process by which organisms that are best fit for their environment are most likely to survive and reproduce. This is possible because of variation in the genetic traits between individuals in a population. After many generations, the traits that enhance survival become more widespread throughout the population over those that do not. Once all the members of a species have these favorable traits then it would be referred to as an adaptation. This selection has occurred with nearly every species on Earth. The Galapagos medium ground finch, for example, developed a beak shape that is different from other finches on the island. This adaptation occurred due to different food sources.