Gombrich not only has all the most relevant information 
about the rise of the pictorial mode; he has all the right 
difficulties. He ends his Art and Illusion  by commenting (pp. 
117­18):

     There is finally the history of Greek painting as we can 
     follow it in painted pottery, which tells of the discovery of 
     foreshortening and the conquest of space early in the 
     fifth century and of light in the fourth. . . . Emanuel Loewy 
     at the turn of the century first developed his theories 
     about the rendering of nature in Greek art that stressed 
     the priority of conceptual modes and their gradual 
     adjustment to natural appearances. . . . But in itself it 
     explains very little. For why was it that this process 
     started comparatively so late in the history of mankind? 
     In this respect our perspective has very much changed. To