What are the grounds for believing that the Malthusian constraint has been vanquished for the long horizon? None at all that I can see. Under Malthusianism, the mechanism of mean reversion is obvious. But if we have exactly as many children who survive to reproduce as is convenient to us, what guarantees that we will choose exactly replacement? Or a little less than replacement? Or a little more?

I fear that the answer to this question will be disagreeable. But this is surely the most consequential question in human society, more consequential even than global warming. The person who can answer it will deserve a dozen Nobel prizes, and if you can steer a PhD candidate toward a successful answer then you will have achieved, by proxy, an immortal victory.

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That with modern birth control and long life expectancy, human population appears to head for—or head below—zero population growth. But this does assume that technology can substitute for resources and deliver ever-rising living standards indefinitely. When that fails, Malthus returns in a different form...

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Reproduction below replacement is clearly not a stable equilibrium. Human society is heterogeneous with respect to reproductive propensity. That is to say, selection operates on humans as strongly on us as on fruit flies, but it seems that selection will operate on cultural rather than genetic features ...

What we would like is a cultural system with a mean reversion level of population freely chosen, rather than a level dictated by available resources. But so far as I know, that is not even a dream in our discourse ...

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