NATURAL SELECTION AND EVOLUTION A. The Role Of Natural Selection Evolution is the continuous genetic adaptation of a population of organisms to its environment over time. Evolution results when there are changes in genes present in a population . There are three factors that interact to determine how a species changes over time: environmental factors that affect organisms, sexual reproduction among the individuals in the gene pool, and the generation of genetic variety within the gene pool. The idea that some individuals whose gene combinations favor life in their surroundings will be most likely to survive, reproduce, and pass their genes on to the next generation is known as the theory of natural selection. The theory of natural selection was first proposed by Charles Darwin and Alfred Wallace and was clearly set forth in 1859 by Darwin in his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Stru...