"I believe that the arts which aim at imitating the creations of nature originated in the following way: in a tree trunk, a lump of earth, or in some other thing were accidentally discovered one day certain contours that needed only a very slight change to look strikingly like some natural object. Noticing this, people tried to see if it were not possible by addition or subtraction to complete what still was lacking for a perfect likeness. Thus by adjusting and removing outlines and planes in the way demanded by the object itself, men achieved what they wanted, and not without pleasure. From that day, man's capacity to create images grew apace until he was able to create any likeness, even when there was no vague outline in the material to aid him."
On Sculpture by Leon Battista Alberti (1464)