People are having fewer children later in life. What do smaller families mean for society? : Everyone loves a mystery, and today we have one for you. Why are birthrates falling across so much of the world? We once feared cataclysmic overpopulation. Now it seems the global population might shrink before the end of the century. No one has definitive answers. But in exploring the issue in a series of stories this week, Simon Montlake is asking the important questions about how it might reshape our world.