There are few things more important than fertility in determining a nation's future viability.Demographers suggest that a country needs a fertility rate of just over two children per woman to hit "replacement fertility" - the rate at which new births fill the spaces left behind by deaths.
But because of certain cultural and economic forces, only about half of the world's 224 countries currently hit replacement fertility.
For those that don't, encouraging people to have sex can involve strategies that range from highly explicit to downright bizarre.