Newly returned from a week in Paris and well sated with delicious cheeses, magnificent art, and glorious (inexpensive!) wines, one is disinclined to reflect upon the decline of Europe. But the demographic reality so scathingly limned in Mark Steyn’s America Alone cannot be long avoided. Those adorable French babies are not quite as scarce as, say, Lithuanian ones (a 2.1 total fertility rate is required for a society to maintain itself — Lithuania’s rate is 1.2), but...