Is Population Growth Good or Bad? Posner's Comment
There is much in Becker's posting with which I agree, in particular that population growth will not cause us to run out of natural resources. I also agree that a combination of preventing carbon dioxide emissions from reaching the atmosphere and removing carbon dioxide from the atmosphere may eventually (though possibly at enormous cost, and possibly too late) solve the global-warming problem; this is an issue that I have addressed in my book on catastrophe.
And yes, increasing the extent of the market does permit greater specialization (hence lower costs and prices) and tends to increase the innovation rate by enabling the fixed costs of innovation to be spread further, although the extent of the market depends on incomes and not just on population. But innovation is a mixed blessing. It is like evolution (which in fact it resembles) in having no necessary relation to social welfare. The technologies of warfare are merely the most obvious example. The benefits of (for example) medical technology accrue mainly to the elderly, and by extending the life of the elderly advances in that technology increase their political heft, resulting in still more redistribution from young to old. Although historically the net social benefits of technological progress have been positive, there is no compelling theoretical reason to expect this always to be the case. The smallpox virus will be synthesized within five years, at which point the destructive capabilities of terrorists will jump by orders of magnitude.
Becker argues that the effect of medical technology in keeping people alive longer can be offset by population growth. That is true if the growth results from a high birthrate. But there are no prospects for even a replacement-level birthrate in Europe and Japan, and I do not think Becker would support efforts to subsidize births in order to offset the growth in the relative size of the elderly population. It seems that the only way in which these countries can sustain a youthful population is by immigration, which seems no longer to be an attractive option for Europe and has never been one for the insular Japanese.
I think Becker himself is at least slightly ambivalent about the effects of an ever-growing world population, because he seems to approve of the effect of female education in lowering the birth rate. And I wonder whether he actually thinks that it's a mistake for China to limit the growth of its population. I do not mean that the "one child" policy is sensible; but I do think it is plausible that the net effect on social welfare of a greater population in that country would be negative (why else is the Chinese government enforcing such an unpopular policy?). Finally, as I discuss in my book and mentioned in passing in my posting on sustainable growth, there is much cause to worry that depletion of species--a consequence in large part of human population growth--will have long-term negative effects on human welfare.
A neglected negative effect of population growth is on political governance. There seem to be strong diseconomies of scale in government. Increases in population, and concomitant increases in economic activity, crime, demand for medical services, and so forth make the job of government more difficult. What seems to be an incipient crisis of competence in the U.S. government may be at least distantly related to the doubling of the U.S. population since 1948.