By Roger Bacon, “There is no true generation, but of things agreeing in nature. So that things be not made but according to their natures. The elder or oak trees will not bring forth pears; nor can you gather grapes of thorns, or figs of thistles, things bring not forth, but only their like, or what agrees with the in nature, each tree its own fruit.
Thus the wise man does that by art in a short time, which nature cannot perform in less than the revolution of a thousand years.
Yet notwithstanding, it is not we that make the metal, but nature herself that does it.
Nor do or can we change one thing into another; but it is nature that changes them.
We are no more than mere servants in the work.”
The Root of the World, by Roger Bacon, 13th Cen.