When John Maynard Keynes was five, his great-grandmother wrote to him, "You will be expected to be very clever, having lived always in Cambridge." The advice came late. Precocious Maynard, with the assistance of his father, a Cambridge don, had already begun collecting stamps and would soon go on to collect butterflies, pen nibs and numbers. Any numbers. Cricket statistics, people's heights and weights, train schedules.
Still, it took a while for the very clever boy to tally his sums and become an economist: he did not read Adam Smith until he was 27, and it took him even longer to...