As I’ve posted elsewhere, I wanted to demonstrate here the strong inverse relationship that exists between population density and fertility rates. As before, this is best done graphically (from Eurostat):
As can be seen here, with a few exceptions (particularly the Low Countries and the UK), there is a strong inverse relationship between population density and total fertility rate (TFR). It even holds in non-European Turkey. This is primarily because when population density is high, cost of living is high, hence having children become an expensive enterprise, in accordance with Steve Sailer’s affordable family formation theory. These maps have a few caveats, in that—in Western Europe especially—some of this reported fertility comes from non-European immigrants, which is almost certainly the case with the apparently fecund UK, and a good deal the case with purportedly prolific France as well. Indeed, Muslim births seem to be responsible for the high fertility rates seen in the crowded but fecund Low Countries.
However, the pattern holds in East Asia as well—in Japan:
(I would have included South Korea as well, but I couldn’t find a map of its TFR broken down by region. I excluded mainland China because of its one-child policy.)
In accordance with my Pioneer Hypothesis, fertility rates in Europe and East Asia are low because these regions are populated by people who do not descend from recent immigrants, having inhabited these areas since ancient times by in large. Hence, natural selection has favored slowly reproducing individuals (who are only marginally “natalist” to even “anti-natalist”), to keep population under control. But, as can be seen, from the above maps, in general, in areas where habitable land is abundant, fertility rates are higher, as the cost of having children is significantly lower.
The main reason fertility has declined in the developed world is not, fundamentally, because of irreligiosity or excessive materialism (those are merely expressions of the underlying mechanism), but as a response to this:
Slow-breeders are simply more sensitive to environmental inputs when it comes to reproduction, and are more easily dissuaded from breeding.
The Pioneer Hypothesis predicts that, in all these countries, if left to their own devices (i.e., without high-fertility immigrants streaming in), fertility will eventually rebound as the land depopulates and cost of living drops (with fast-breeders coming to make up a higher share of the population), as appears to currently be the case in Eastern Europe (see the previous link). Without immigrants, and even with the technological and social upheavals as of late, this process would exist in a stable negative feedback loop (at least for the foreseeable future). Of course, the quantity of people is a separate issue from their quality, as per the topic of my previous post.
Edit, 9/04/12: See this neat follow-up by The Audacious Epigone.