The Roots of Progress

The Malthusian Trap, analyzed

May 23, 2017

After writing on the Malthusian Trap, I solicited comments from some friends who are knowledgeable about economics. One thing they confirmed for me is that, yes, it’s literally true that (at least in some places and times, such as Ireland in the early 1800s?) a man’s land would be divided up among his descendants, so that each generation was farming a smaller plot until they could barely sustain themselves.

I also went and read the first few chapters of Malthus’s original book, An Essay on the Principle of Population.

After all this, my general conclusion is that the idea of population growth bumping up against resource limits is real, but that it needs reformulation.

Here again is the formulation from that Atlantic article, the key phrase being “stable supply”:

If lots of people died, incomes tended to go up, as fewer workers benefited from a stable supply of crops. If lots of people were born, however, incomes would fall…

Malthus himself seems to have been a little better: he at least allowed that production could be increased; he just assumed that it could be increased at most linearly. He doesn’t seem to have had much basis for this, except for an argument from failure of imagination:

If I allow that by the best possible policy, by breaking up more land and by great encouragements to agriculture, the produce of this Island may be doubled in the first twenty-five years, I think it will be allowing as much as any person can well demand.

In the next twenty-five years, it is impossible to suppose that the produce could be quadrupled. It would be contrary to all our knowledge of the qualities of land. The very utmost that we can conceive, is, that the increase in the second twenty-five years might equal the present produce. … The most enthusiastic speculator cannot suppose a greater increase than this.

(From the aforementioned Essay, chapter 2. To be fair, the whole of human history up to that point (1798) seemed to bear him out.)

What both formulations gloss over is the fact that humans work to create their own sustenance.

With that fact firmly in mind, the notion of a constant level of production in the face of a rising population, or that of an arithmetically increasing level of production with a geometrically increasing population, implies diminishing productivity per capita as population increases. So what would cause this?

Causal factors might include limits on:

Some part of these limits was technological, some political (e.g., the power of guilds), and some philosophical (tradition and custom).

That formulation I can believe and understand. The “static pool of wealth” theory is simplistic.

Turning Malthus’s principle around, we can say this: In order to support an exponentially growing population, and indeed to increase that population’s quality of life, technology and society have to exponentially increase our ability to take advantage of the resources of the earth. They need to advance fast enough for per-capita productivity to increase, even as the population overall increases and we have to make use of marginal resources.


Thanks to Ray Niles and Rob Tarr for their comments, which influenced this post.

Social media link image credit: Kravietz, CC BY-SA 3.0