Big Idea 1: The process of evolution drives the diversity and unity of life Enduring Understanding 1.A- Change in the genetic makeup of a population over time is evolution Essential knowledge 1.A.1: Natural selection is a major mechanism of evolution According to Darwin's theory of natural selection, competition for limited resources results in differential survival. Individuals with more favorable phenotypes are more likely to survive and produce more offspring thus passing traits to subsequent generation. (Fitness) Evolutionary fitness is measured by reproductive success Genetic variation and mutation play roles in natural selection. A diverse gene pool is important for the survival of a species in a changing environment.