DOES not the fact that all of the things which furnish man's subsistence have the power to multiply many fold — some of them many thousand fold, and some of them many million or even billion fold — while he is only doubling his numbers, show that, let human beings increase to the full extent of their reproductive power, the increase of population can never exceed subsistence? This is clear when it is remembered that though in the vegetable and animal kingdoms each species, by virtue of its reproductive power, naturally and necessarily presses against the conditions which limit its further increase, yet these conditions are nowhere fixed and final. No species reaches the ultimate limit of soil, water, air, and sunshine; but the actual limit of each is in the existence of other species, its rivals, its enemies, or its food. Thus the conditions which limit the existence of such of these species as afford him subsistence man can extend (in some cases his mere appearance will extend them), and thus the reproductive forces of the species which supply his wants, instead of wasting themselves against their former limit, start forward in his service at a pace which his powers of increase cannot rival. If he but shoot hawks, food-birds will increase: if he but trap foxes the wild rabbits will multiply; the bumble bee moves with the pioneer, and on the organic matter with which man's presence fills the rivers, fishes feed. — Progress & Poverty — Book II, Chapter 3: Population and Subsistence: Inferences from Analogy
read the corresponding passage in Bob Drake's abridgement:
The strength of the reproductive force in the animal and vegetable kingdoms is constantly cited, from Malthus to current textbooks. For instance, if protected from their natural enemies, a single pair of salmon might fill the entire ocean, or a pair of rabbits overrun a continent. Many plants scatter seeds by the hundreds, and some insects deposit eggs by the thousands. Each species constantly tends to press against the limits of subsistence, and when not limited by its enemies, apparently does so.
These examples attempt to prove that human population also tends to press against subsistence. Unless restrained by other means, this must necessarily result in low wages and poverty. And if that is not enough, then actual starvation will keep it within the limits of subsistence.
But is this analogy valid?
The human food supply is drawn from the animal and vegetable kingdoms. The reproductive force in the vegetable and animal kingdoms is greater than among humans. Hence, this analogy simply proves the power of subsistence to increase faster than population. All of the things that furnish human subsistence have the power to multiply many fold, sometimes a million fold. Meanwhile, humanity is merely doubling (even according to Malthus). Doesn't this show that even if human beings increase to the full extent of their reproductive power, population can never exceed subsistence?
There is one additional fact. The actual limit to each species lies in the existence of other species: its rivals, its enemies, or its food.
Humans, however, can extend the conditions that normally limit those species giving our sustenance. (In some cases, our mere appearance will accomplish this.) The reproductive forces of these species then begin to work in service of humans. This increase continues at a pace that our own powers of increase cannot rival. If we shoot hawks, birds will increase; if we trap foxes, rabbits will multiply.
This distinction between humans and all other forms of life destroys the analogy. Of all living things, only humans can manipulate reproductive forces stronger than their own to supply themselves with food. Bird, insect, beast, and fish take only what they find. They increase at the expense of their food. But the increase of humans will increase their food. The population of the United States, once small, is now forty-five million. Yet there is much more food per capita.
It is not the increase of food that has caused the increase of humans -- rather, the increase of humans has brought about an increase of food. There is more food simply because there are more people. This is the difference: Both humans and hawks eat chickens -- but the more hawks, the fewer chickens; while the more humans, the more chickens.