Iconography becomes even more revealing when processes or concepts, rather than objects, must be depicted for the constraint of a definite 'thing' cedes directly to the imagination. How can we draw 'evolution' or 'social organization,' not to mention the more mundane 'digestion' or 'self-interest,' without portraying more of a mental structure than a physical reality? If we wish to trace the history of ideas, iconography becomes a candid camera trained upon the scholar's mind.