They deal with this issue in his book.
I like a quote by Michelangelo best:
"To copy each one of those things after its kind seems to me to be indeed to imitate the work of God; but that work of painting will be most noble and excellent which copies the noblest object and does so with the most delicacy and skill. And who is so barbarous as to not understand that the foot of a man is nobler than his shoe, and his skin nobler than that of the sheep with which he is clothed, and not be able to estimate the worth and degree of each accordingly?"
