noun, plural: evolutions
In order for evolution to occur, there must be genetic variation. Genetic variation brings about evolution. Without it there will be no evolution. There are two major mechanisms that drive evolution. First is natural selection. Individuals with advantageous traits are more likely to reproduce successfully, passing these traits to the next generation. This kind of evolution driven by natural selection is called adaptive evolution. Another mechanism involves genetic drift, which produces random changes in the frequency of traits in a population. Evolution that arises from genetic drift is called neutral evolution.
See also: Darwinism.