These days, it's lonely at the top. For 5,000 years, nearly everyone agreed that the best thing in life was to belong to elites of birth and wealth. "When the poor catch sight of [the elite] they murmur, they groan, they praise," St. Augustine wrote in the fifth century. "In between their praises, they say: 'These are the only ones who matter; these are the only ones who know how to live." But now everything seems to be different. The world appears to have passed a great watershed. Today, only merit matters. Privilege gained by birth or marriage has become a drawback....