The Malthusian Doom is really problem number one in the study of Economics; not unemployment or The Great Depression or Stagflation. The problem comes in two or three different flavors, the most basic being the simple observation that population has a tendency to compound, and grow in a geometric pattern, while production of necessities has no such tendency and so grows more or less linearly. If a population is growing, its growth tends to actually accelerate, simply because if each couple produces an average of 2.5 children (for example), the following generation is larger, and so the following round of 2.5 children per couple is applied to a larger number of couples, and so the growth is compounded each generation. The danger of this is that eventually such acceleration must cause population to overrun the production of necessities, and starvation begin to hit.
That is the most basic version, in fact I heard it elementary school. In that description, the crisis point seems to be projected way off in the future somewhere. A subtler version of the same problem is to suggest (during the bad times this is sometimes suggested) that we have already hit the crisis point, and that the level of economic hardship in the world is a consequence of population being too great. The implication of this conception of the Malthusian Doom is that we are witnessing population straining to grow higher but being held back by scarcity. This implies that any effort to reduce the scarcity will fail to improve quality of life, but will succeed in increasing population. If a million more bushels of wheat are produced, they will not, in this vision, reduce hunger at all because more mouths will simply be produced to consume that wheat, and we’ll be right back where we started.
To me, the most interesting thing about the Malthusian Doom is how wrong it is about everything. Population does not necessarily grow geometrically; production does not necessarily or even generally grow linearly. The revelation that economic growth is a compounding phenomenon has been a great ray of hope to economists, but it has long been known that procreation is a voluntary function and not bound to behave in any particular way, especially a self-destructive and counter-incentive way. The stabilizing or even declining populations of modern societies unaffected by starvation simply makes empirically obvious GK Chesterton’s remark on Malthus in 1927: “Nothing depending on the human will can proceed by geometrical progression, and population certainly does not proceed by anything of the sort.”