In the roughly 250 years since the Industrial Revolution the world’s population, like its wealth, has exploded. Before the end of this century, however, the number of people on the planet could shrink for the first time since the Black Death. The root cause is not a surge in deaths, but a slump in births. Across much of the world the fertility rate, the average number of births per woman, is collapsing. Although the trend may be familiar, its extent and its consequences are not. Even as artificial intelligence (AI) leads to surging optimism in some quarters, the baby bust…