Many organisms that once lived are now extinct. Organisms vary, and these variations are inherited, at least in part, by their offspring Organisms produce more offspring than can possibly survive. There must be differential survival and reproduction associated with the possession of that trait.
Natural selection can only choose among existing variation in a population.
Ultimate or new source of variation. The proposed mechanism is still somewhat theoretical. Probably because of profound philosophical implications. The path of evolution and the observed harmony of nature is without purpose. Evolution is not inherently progressive.