But there is no reason to think that GDP would fall along with population. The capital base of society, its productive plant as broadly understood, will not dissolve as population declines. Moreover, assume that population fell but GDP fell less — or even grew. Per capita GDP would rise and, by that measure, the population would be more prosperous than before.

One of the key variables mitigating the problem of decreasing population would be continuing advances in technology to increase productivity. We can call this automation or robotics, but growths in individual working productivity have been occurring in all productive environments from the beginning of industrialization, and the rate of growth has been intensifying. Given the smooth and predictable decline in population, there is no reason to believe, at the very least, that GDP would not fall less than population. In other words, with a declining population in advanced industrial societies, even leaving immigration out as a factor, per capita GDP would be expected to grow.

Changes in the Relationship Between Labor and Capital

A declining population would have another and more radical impact. World population was steady until the middle of the 16th century. The rate of growth increased in about 1750 and moved up steadily until the beginning of the 20th century, when it surged. Put another way, beginning with European imperialism and culminating in the 20th century, the population has always been growing. For the past 500 years or so, the population has grown at an increasing rate. That means that throughout the history of modern industrialism and capitalism, there has always been a surplus of labor. There has also been a shortage of capital in the sense that capital was more expensive than labor by equivalent quanta, and given the constant production of more humans, supply tended to depress the price of labor.

For the first time in 500 years, this situation is reversing itself. First, fewer humans are being born, which means the labor force will contract and the price of all sorts of labor will increase. This has never happened before in the history of industrial man. In the past, the scarce essential element has been capital. But now capital, understood in its precise meaning as the means of production, will be in surplus, while labor will be at a premium. The economic plant in place now and created over the next generation will not evaporate. At most, it is underutilized, and that means a decline in the return on capital. Put in terms of the analog, money, it means that we will be entering a period where money will be cheap and labor increasingly expensive.

The only circumstance in which this would not be the case would be a growth in productivity so vast that it would leave labor in surplus. Of course if that happened, then we would be entering a revolutionary situation in which the relationship between labor and income would have to shift. Assuming a more incremental, if intensifying, improvement in productivity, it would still leave surplus on the capital side and a shortage in labor, sufficient to force the price of money down and the price of labor up.

That would mean that in addition to rising per capita GDP, the actual distribution of wealth would shift. We are currently in a period where the accumulation of wealth has shifted dramatically into fewer hands, and the gap between the upper-middle class and the middle class has also widened. If the cost of money declined and the price of labor increased, the wide disparities would shift, and the historical logic of industrial capitalism would be, if not turned on its head, certainly reformulated.

We should also remember that the three inputs into production are land, labor and capital. The value of land, understood in the broader sense of real estate, has been moving in some relationship to population. With a decline in population, the demand for land would contract, lowering the cost of housing and further increasing the value of per capita GDP.

The path to rough equilibrium will be rocky and fraught with financial crisis. For example, the decline in the value of housing will put the net worth of the middle and upper classes at risk, while adjusting to a world where interest rates are perpetually lower than they were in the first era of capitalism would run counter to expectations and therefore lead financial markets down dark alleys. The mitigating element to this is that the decline in population is transparent and highly predictable. There is time for homeowners, investors and everyone else to adjust their expectations.

This will not be the case in all countries. The middle- and third-tier countries will be experiencing their declines after the advanced countries will have adjusted — a further cause of disequilibrium in the system. And countries such as Russia, where population is declining outside the context of a robust capital infrastructure, will see per capita GDP decline depending on the price of commodities like oil. Populations are falling even where advanced industrialism is not in place, and in areas where only urbanization and a decline of preindustrial agriculture are in place the consequences are severe. There are places with no safety net, and Russia is one of those places.

The argument I am making here is that population decline will significantly transform the functioning of economies, but in the advanced industrial world it will not represent a catastrophe — quite the contrary. Perhaps the most important change will be that where for the past 500 years bankers and financiers have held the upper hand, in a labor-scarce society having pools of labor to broker will be the key. I have no idea what that business model will look like, but I have no doubt that others will figure that out.