On Twitter today, I was asked:
The article in question has an interesting analysis.
1. What is the "Muslim world"? In total, there are about 1.7 billion Muslims in the world today; 80% (1.37 billion) are found in a handful of countries (shown on the chart below). While Muslims make up the majority of many of these countries, several are not Muslim-majorities: India (14%), Nigeria (45%), Ethiopia (34%), China (2%), Russia (12%).
2. Is fertility falling in these countries? Fertility rates are measured as the number of children per woman. This data is tracked by the United Nations in its regular population forecasts. The Hoover article, in 2012, argued fertility among Muslims would fall to levels lower than non-Muslim counterparts--that the then-UN figures were overestimated. The new 2015 Population Prospects estimated the following fertility rates for 2010 (blue) and 2050 (red) for each of these countries:
What happens to fertility rates in the "small" Muslim populations really doesn't affect the global result. Population trends among the Big 8 are the ones to watch. The estimate projects the total fertility rate in 2050 to be 1.9 in North America and 1.75 in Europe. While the estimate doesn't seem to think fertility will fall across the board in all Muslim countries, it does estimate an equivalent fertility rate for five of the Big 8 Muslim populations (Indonesia, India, Bangladesh, Iran, and Turkey), while projecting higher rates in Pakistan, Nigeria and Egypt.
What is the end result of falling fertility rates? Will Islam decline? The Hoover article did not project a result in terms of population. But if we use the UN's new estimate and maintain the current % Muslim in each of the above countries, their Muslim populations in 2050 would total to 2.3 billion (this is in line with the projection of the Center of the Study of Global Christianity of 2.6 billion globally), out of 9.7 billion total (about 23%). Even with these declining fertility rates, then, we are not looking for a decline in the total number of Muslims. In fact, the current estimate is for an increase of nearly 900 million by 2050.