In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual.
The theory of natural selection is the centerpiece of The Origin of Species and of evolutionary theory. It is this theory that accounts for the adaptations of organisms, those innumerable features that so wonderfully equip them for survival and reproduction; it is this theory that accounts for the divergence of species from common ancestors and thus for the endless diversity of life. Natural selection is a simple concept, but it is perhaps the most important idea in biology.
Mosts scientist are unable to arrive at a specific definition of biological evolution. “Biological evolution is… change in the properties of populations of organisms (you and me) that [happen during] the lifetime of a single individual. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next
