Concept 12 Evolution begins with the inheritance of gene variations.

Key to the theory of evolution by natural selection are new trait variations that arise spontaneously and make an organism more competitive in the struggle for survival. Following publication of Darwin's On the Origin of Species, in 1859, field stations were established where scientists could study the unique characteristics of organisms that had evolved to inhabit different environments. However, field observation could not explain the origin of variation or how new traits are inherited.

The new sub-discipline of experimental evolution emerged at the turn of the 20th century with the goal to recreate evolution in controlled experiments with agricultural plants and animals. It soon became clear that mutations in genes are the source of variation and that Mendelian genetics offered a statistical method for analyzing the inheritance of new mutations. By the early 1920's, experimental evolutionists had quietly become the first generation of geneticists.