The Encyclopedia of Evolution. by Richard Milner

Pages 157- 160

By "evolution" biologists mean that the change in gene frequencies of populaions over the generations in time produces new species.
Darwin called it "descent with modification": a slow process, usually operating over hundreds of thousands, and even millions, of years.

There are four commonly confused meanings of evolution, which should be kept separate and distinct:

1. The general process of populational and species change, which is considered an established scientific fact;
2. Inevitable "progress"from lower to higher life forms, a discredited notion;
3. the particular histoory of the "branching bush" of life and the origin of various groups, or phylogenies, which are interpreted from the fossil record and biochemical studies; and
4. the mechanism, or "engine," of evolution, which Darwin and Wallace proposed as "natural selection," but which is currently being investigated and modified by research.



That is how the book started out.