Evolution is the process by which organisms change over time. Mutations produce genetic variation in populations, and the environment interacts with this variation to select those individuals best adapted to their surroundings. The best-adapted individuals leave behind more offspring than less well-adapted individuals. Given enough time, one species may evolve into many others.
1: A process of change in a certain direction <tumor evolution and progression -- I. J. Fidler et al>.
2. A: The historical development of a biological group (as a race or species): phylogeny. B: A theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations.