| rich people have to buy sculptures made of human dung just to keep up.

This explanation of modern art seems incomplete. For many artists now, bleeding edge art is an exercise in "conceptual" problem solving and game-playing. (For discussion see, e.g., Kosuth 1969.) The economic forces described by Bell/Pinker do put selection pressure on which art gets distributed, displayed and, to a small extent, produced. But to describe these pressures without some reference to the noble and useful productions behind them seems to imply the common error of dismissing modern art as a bluff, a bullshit or some other mostly-useless activity.