Natural selection occurs through a 5 step process: 1) Variation exists within populations, 2) Organisms compete for limited resources, 3) Organisms produce more offspring than can survive, 4) Genetic traits are passed to offspring, 5) Those organisms with traits most beneficial to survival and reproduction are more likely to survive and reproduce. The document also lists key terms related to biological evolution such as mass extinction, homologous structures, and vestigial structures.