Andrew Sabl at Reality Based Community tries to deflate some of the panic over declining populations in Western Europe. I think he misfires on a couple points: Other things equal, cultural dynamism will tend to vary with population size for the familar reason that division of labor depends on the extent of the market. A society consisting of a few thousand people isn't going to be able to support rich communities specializing in different kinds of artistic or scientific production to the same extent a larger one can—though there are very likely sharply diminishing returns to scale here. The key point, though, is that it's silly to freak out over dire scenarios that emerge when you do straight-line extrapolations of current trends. As Sabl notes, for instance, if people are having fewer children partly because population density makes larger houses prohibitively expensive, you can't just presume they'll continue reproducing at the same rate indefinitely, because less dense populations will lower housing prices, and the opposite effect will kick in.