Evolution, at least the model thereof, wasn't handed down by some omnipotent being, since the definition excludes such a being. Rather, it was developed in spurts by many people from at least 600 B.C., culminating with Darwin, the synthesizer of all the ideas. Simply put, the source is man.
Below are various ideas pertaining to the evolutionary model (some are dated and rejected today but helped form the foundation), the people who originated them, and my comments.
- Water (a secondary cause) was the origin of everything - Thales, section 3. Water is indeed a reducing agent (the Miller-Urey experiments required a reducing atmosphere) and is used in many biological reactions.
- One species can become another species over time - Anaximander, bottom of page. The definition of "species" has been in at least a little flux for quite some time now, but this concept is definitely a building block in the evolutionary model.
- Chance (a secondary cause) is a productive force by itself - Empedocles, top half of page. There's a technical definition of "chance" used by scientists in a slightly different way than the rest of the population uses it, but look at the web page and see what its understanding of "chance" is.
- Spontaneous generation (life from non-life) is a mechanism to produce life - Aristotle. At the bottom of the page is something interesting: while Pasteur's experiments demonstrated that life cannot under today's conditions (an oxidizing atmosphere, different gas proportions, etc.) originate from dead organic matter, scientists hold firm that it could have under different conditions. It must have, in order for the evolutionary model to be true. But those conditions are for another day.
- Uniformitarianism is a main process through history - Hutton and Lyell, both geologists. Again, this will be discussed in more detail on another day. But Hutton's reasoning behind a conclusion of uniformitarianism is very interesting. Go read it.