Gigantic Inevitable Famine
Malthus predicted dire consequences for humanity due to the superior (exponential) power of population over (linear) food supply:
"The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction; and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague, advance in terrific array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world." (my bolding)
Malthus provides a classic example:
"Taking the population of the world at any number, a thousand millions for instance, the human species would increase in the ratio of - 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. and subsistence as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 etc. In two centuries and a quarter, the population would be to the means of subsistence as 512 to 10: in three centuries as 4096 to 13, and in two thousand years the difference would be almost incalculable, though the produce in that time would have increased to an immense extent."
Here's Malthus' comparison of the global human exponential population increase and the linear food supply failing miserably to keep up, resulting in famine:
|Available Food Supply||1||2||3||4||5||6||7||8||9||10||11||12||13|
|Ratio of Population to Food Supply||1:1||2:2||4:3||2:1||16:5||4:1||64:7||16:1||256:9||
Table A. Malthus' example of exponential growth of global human population and linear food supply out of balance - there is famine
In my article Malthus - An Exponentialist View and Linear Growth Versus Exponential Growth I explain why I believe Malthus to be wrong. As hinted at by Malthus himself, and in direct contradiction to his assertion that food supply was arithmetic or linear, food supply is also exponential. Also, the true nature of exponential growth is only revealed when we examine variable rates of growth - see What Is Exponential? for more. Essentially it is possible to demonstrate that variable rates of population growth are just as exponential in nature and therefore just as powerful as constant rates of population growth.
The question remains then, if food is exponential and population growth is exponential why do we need to worry about "gigantic inevitable famine" at all?
There are two parts to the answer:
Limits To Growth
In terms of evolutionary theory, fitness (as in "the survival of the fittest") is measured by the population growth rate which is also known as the Malthusian Parameter. Hence, the greater the growth rate the "fitter" a population is. However, what is not commonly appreciated is that fitter populations (those with the highest growth rates) are thrust towards their own limits to growth faster than less fit populations (those with positive growth rates smaller than the fittest populations). Hence evolutionary fitness, as measured by the Malthusian Parameter, is both a Malthusian blessing and a Malthusian curse. Perhaps the wisest course might be sustainable growth within local limits to growth...
I examine Malthus' introduction of the concept of Limits To Growth in his treatment of the Earth as a finite resource in Population Doubling - The Earth. This is echoed in the works of other Famous Exponentialists. Malthus' own treatment depended upon an imbalance between linear food supply and exponential population increase. We know this is incorrect, as food supply also increases exponentially and is thus capable - but not guaranteed - of keeping pace with (or even exceeding) population increase.
My own treatment of the Earth as a finite resource is my article Human Global Ecophagy, which examines how quickly could humans (theoretically) consume the entire planet.
Limits to growth are real and cannot be avoided. Hence, as any population of any species increases it will inevitably face its own limit to growth.
Exponential Growth Versus Exponential Growth
The following tables show just three of an infinite variety of possibilities that examine the balance of exponential forces between a population and its food supply. For simplicity's sake I use the standard exponential series (which could represent thousands, millions, billions etc) to illustrate my point, but in reality all the numbers in between might also apply. However, I believe these three basic scenarios capture the essence of the problem of balancing exponential forces against one another.
In Table B we see that the population and food supply are in balance, and hence there is no food glut and no famine. Nobody need die from famine in such a scenario.
(Food / Population)
Table B. Exponential growth of population and food supply are in balance - no glut and no famine
In Table C we see that the population and food supply are out of balance, with a glut in the food supply. Again, nobody need die from famine in such a scenario.
(Food / Population)
Table C. Exponential growth of population and food supply out of balance - there is a food glut
In Table D we see that the population and food supply are again out of balance, this time with a shortage in the food supply. Gigantic Inevitable Famine is now ready to "level the population of the world" as Malthus advised.
(Food / Population)
Table D. Exponential growth of population and food supply out of balance - there is famine
The purpose of these three scenarios is to illustrate how an imbalance between the exponential food supply and exponential population increase can result in famine that is just as devastating the imbalance between linear food supply and exponential population increase proposed by Malthus. This can apply to any population of any species (including a human population) and its food supply.
The balancing of exponential forces is a precarious business, even for a species as clever as humanity.