A decade ago, the psychiatrist Peter Kramer published a book called Listening to Prozac, which claimed that our understanding of neurochemistry was so advanced that we would soon be able to design- and no doubt to vary- our personalities according to our tastes. Henceforth there would be no more angst. He based his prediction upon the case histories of people given the supposed wonder drug who not merely recovered from depression but emerged with new, improved personalities. Yet the prescription of the drug (and others like it) to millions of people has not noticeably reduced the sum total of human...