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My 2011 book How Civilizations Die (and Why Islam is Dying, Too) assembled evidence that the decline of Islam as a religion explained collapsing fertility, just as the decline of Catholicism explained collapsing fertility in lands once blessed by large families — Spain, Italy, Poland, Ireland, and Quebec. Iran’s total fertility rate plunged to an estimated 1.6% in 2010, barely above Europe’s rate of 1.5 children per female. In 1979, when the Islamists took power in Iran, the average woman bore seven children. Nothing like this sudden snapping shut of the national womb has ever happened before in all of history. And the rest of the Muslim world is headed in the same direction.