Is it worth pointing out that there is a positive correlation between belief and birthrate?

Places where most of the people are religious (Red State US, Muslim world) have positive growth rates. Post-religious societies (Blue State US, Canada, and Western Europe) have negative growth rates.

One interesting thing is that Russia, which was atheistic under Communist rule, has been returning to Orthodox Christianity over the last ten years -- and the Russian birthrate has begun increasing in the last three or four years.

BTW, the effect is quite noticeable in the US. The deep blue states (NY, New England, and the Pacific Coast) have almost European birthrates. The Bible Belt states make up for that difference -- enough so that the US still has a positive birthrate. And yes, these are births to parents of natural-born American citizens, not those coming from south of the border.
 

The increasing Russian birth rate may be coming too late to save them. I've heard that the Chinese are simply walking (or the equivalent) into some parts of Siberia and squatting. Also, given that the death rate is very high among middle-aged men, Russia may soon (ten years or so) run short of conscripts for its military as well as non-coms and middle managers in general.

It's going to get interesting there, in the sense of a giant wreck in which an Amtrak hits a tour bus full of nuns and then has an airliner crash into it interesting.