Adaptation: The evolutionary process whereby an organism becomes better suited to its environment, through the development of physical or behavioral traits that improve its ability to survive and reproduce.
Genetic Variation: The genetic differences that exist within a population, which allow some individuals to have traits that are advantageous in a given environment.
Survival of the Fittest: The principle that individuals or species best adapted to their environment are more likely to survive and reproduce, passing on their genetic traits to subsequent generations.