This is not simply a matter of affordability, the buzzword so often invoked to explain why people are choosing to have smaller families. Government support for parents can help, but overall, people are having fewer children both in countries that offer very little and in those renowned for their generous family benefits; moreover, the trend holds among those who are struggling to make ends meet and among those who, like the Riveras, have advanced degrees and salaried jobs. What unites these disparate cultures, policy environments and demographics, researchers are now realizing, is young people’s inescapable and crushing sense that the future is too uncertain for the lifelong commitment of parenthood. Call it the vibes theory of demographic decline.