A while back, I criticized Mark Steyn for being overly pessimistic about European Demographics. I've just now discovered this article making a similar point more quantitatively.

First, Western nations aren't the only ones with falling birthrates. The Muslim world is seriously declining as well. Iran, Turkey, Algeria, Morocco, Tunisia, Albania, Lebanon, and Malaysia are all below the 2.1 replacement line, while Bangladesh, Egypt, Indonesia, and the Muslim parts of India are close behind and falling rapidly. A few Muslim nations do indeed have high fertility, but the common denominator is not Islam itself, as Steyn implies, but a lack of modernization. Many non-Muslim countries that also haven't fully modernized have high rates as well, such as Laos, Uganda, and Paraguay.
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Europe, on the other hand, is admittedly a trickier case. Native fertility is indeed low, while Muslim growth rates and levels of extremism have remained high. Over the next 50 years, Europe projects to lose about 100 million people, while European Muslims will double their numbers to about 20% of the total European population. If Turkey joins the EU, Muslim numbers will rise even further.

But will this bring Sharia law, as Steyn fears? I don't think so. Even under the most high-growth projection (which is by no means certain), Muslims will remain a minority on the Continent. Their radicals may want Sharia law, but they won't get it at the ballot box.