Cumulative change in the characteristics of organisms or populations from generation to generation. Any pair of organisms produces far more offspring than it needs to replace that pair.
Organisms possess variation.
Variations in the genotype are expressed in the phenotype. These organisms will pass characteristics onto offspring. Through genetic inheritance, these characters persist in offspring. Populations gradually change through time in genotype and phenotype. When changes are so great that organisms can no longer interbreed, a new species is formed.