Then, beginning at mid-century, there was renewed interest in Malthus, as concern about the relation between means of subsistence and population shifted from an economic perspective to a more demographic outlook. Joseph Spengler's voluminous scholarship in both areas (see Spengler, 1972) was transitional, and a number of scholars, including Kenneth Boulding (1966), Lester Brown (1974), Paul and Anne Ehrlich (1970), and Garrett Hardin (1968), began expressing concern about the runaway growth of world population in the sixties and seventies. This rapid growth came to be seen as a result of the exploitation of nonrenewable resources, an idea that had its roots in Malthus's observations about limitations to growth in the means of subsistence. And the eventual consequences seemed likely to be the "positive checks" that Malthus's name evoked for my father--famine, war, and pestilence.
Malthus had lived in an agrarian society that was as yet little changed by the Industrial Revolution, and when he thought about means of subsistence, he thought about land which, if properly treated, would continue to produce a crop, year after year. When he suggested, for purposes of argument, that means of subsistence might increase arithmetically, he was presenting a best-case scenario. And eventually he came to realize that there was an impediment to the continual improvement of productivity: the law of diminishing returns. One might, for example, increase the productivity of a field with acid soil by putting a hundred pounds of lime on it, but another hundred pounds of lime would not increase productivity again by the same amount, and a third hundred pounds would increase productivity even less.
A new viewpoint that has arisen since Malthus's time sees any increase in productivity as temporary and contingent on special conditions, and sees productivity as more likely to diminish. Farmlands erode, mines are worked out, old-growth timber is used up, fisheries are exhausted. It is still true, as Malthus observed, that population rises to the extent that means of subsistence permit. But the stock of resources upon which subsistence depends does not just rise slower than population; it may actually fall as population rises. In fact, resources may diminish because population rises, so that their availability is inversely proportional to population size.
Malthus noted that constraints to the growth of population were eased in new colonies, where means of subsistence are abundant. So he would not have been surprised that world population grew as the Mississippi Valley and other fertile lands were put to the plow. But another factor that Malthus could not have understood caused population to grow even faster. The new technology that was beginning to develop in his day made it possible to use energy from fossil fuels for human purposes. This completely changed the relationship between the labor that individuals can contribute and the goods they consume. Abundant, cheap energy from fossil fuels can leverage the actual physical energy that humans put into economic activities, so that they get an enormous return for their effort. A man driving a tractor can cultivate acres more than a man with a hoe, or even a man with a team of oxen. The effect of cheap energy from fossil fuels is the same as the effect of abundant resources in new colonies, only far more intense. It makes means of subsistence vastly more plentiful and allows population to expand with great rapidity. But reserves of fossil fuels, as well as other resources exploited through their use, appear to be finite. They are not inexhaustible. So while population grows by using them, it also uses them up, steadily bringing closer a day when remaining reserves will be insufficient to supply the existing population (Catton, 1980).
Opposing this bleak view are many economists who believe that there are no limits to growth. They argue that resources cannot just run out, because their availability is a function of demand. It is unrealistic to see resources as simply present or absent; they exist in a range of different grades. Copper, for example, can sometimes be found in its pure, metallic form, and it can also be found in a variety of ores ranging from those that contain a high percentage of copper to those that contain very little. Resources that can be most easily exploited —like pure, native copper— are used first; but a continuing demand results in the development of techniques to exploit resources of lower grade. As long as demand is great enough, resources will always be available.
Central to this view is the belief that whenever new technologies are needed, they will develop. Those who take this position observe that most of the past century's economic growth resulted from technological progress and conclude that the only limiting factor to economic production is knowledge. The essential means of production is neither capital, natural resources, nor labor, but the ability to manage them; and as long as knowledge advances, the economy will continue to expand (Solow, 1970; Drucker, 1993; Sagoff, 1995). Since humans are unique in the way they can use knowledge to construct their own environment, they are immune from the constraints that would limit the population of other animals (Preston, 1986, p. 69). Growth and expansion have always been characteristic of the human species, and there is no reason why humans of the future cannot go on using yet more energy, growing in population, and establishing, if necessary, colonies on other planets.
At the end of the twentieth century, debate about the relationship between population and subsistence is still polarized by the same difference of underlying assumptions that animated the controversy two hundred years ago. On the one hand are those who believe in the perfectibility of man; who think there is something special about human beings that sets them apart from other animals; who believe that humans can decide what their future should be and make it happen. And on the other hand are those who see no evidence that any special ability has exempted human populations of the past from the principles that govern the populations of other species, and see no reason to believe that such an exemption will prevail in the future.
On the one hand are those who believe that science, knowledge, and invention make all things possible; and on the other hand are those —many of them scientists— who believe that there are some natural processes that humans can understand, but not affect. Daniel and Robert Malthus, father and son, are part of a procession that marches in double file down through the centuries. With Daniel, on the left, are Rousseau, Godwin, Condorcet, Marx and Engels, and today's economists of growth. With Robert, on the right, are Voltaire, Darwin, Wallace, Spencer, and those who now see a threat in continued growth. So little progress has been made in resolving the debate that one might suppose the difference between the two columns to be more a matter of predisposition than force of reason.
But, while the underlying assumptions of the parties to the debate have remained virtually the same, many other things have changed in the two hundred years since Malthus wrote his first Essay. Demographic information has accumulated, the population of the world has grown, and the focus of attention has shifted. The essential ideas associated with the name of Malthus are different at the end of the twentieth century than they were in the nineteenth century.
Malthus had very little hard demographic information at his disposal. He did not even know the population of England. In 1798 there were still people who opposed a national census on the grounds that it would disclose to England's enemies the number of troops that she could field in time of war. The population of the world as a whole was completely unknown; earlier in the eighteenth century, in the absence of empirical data, it had been a topic of philosophical debate. Montesquieu (1734) argued that world population had diminished since the days of the ancient Romans, and Hume (1752) argued that it had grown. Malthus, himself, thought that population fluctuated over the long run, growing until it was cut back by positive checks, and then growing again.
In the last two centuries, the taking of censuses has become a common practice and today a wealth of demographic information is available for study. We have a fairly accurate idea of the whole Earth's population, and we know how it is changing. We can make projections about the future, and techniques have even been developed to approximate world population in times past (McEvedy & Jones, 1978, give a popular summary). We know that when Malthus was writing his first Essay, world population was under one billion, and that it is now nearly six billion —and growing.
And in the last two hundred years the focus of attention has shifted away from Malthus's conclusion and settled on his initial postulates. His explanation of why poverty cannot be eliminated from society has been largely forgotten, but the idea that population tends to grow faster than means of subsistence, which he made no pretense of having originated, has become firmly associated with his name.
Indeed, it is sometimes asserted that Malthus was "wrong" because population has grown more slowly than he predicted, while means of subsistence have grown much faster (Winch, 1987, p. 96). But Malthus never predicted that population and means of subsistence would grow at precisely geometric and arithmetical rates; his mathematical examples were only used to call attention to a qualitative difference in the two parameters. As John Stuart Mill (1864, 1, p. 439) pointed out, "every candid reader knows that Mr. Malthus laid no stress on this unlucky attempt to give numerical precision to things which do not admit of it, and every person capable of reasoning must see that it is wholly superfluous to his argument." What is central to his argument is the claim that population always expands to the limits imposed by means of subsistence. And the evidence continues to show that it does. The more food the world produces, the more its population grows.
Finally, this shift to a broader perspective has induced many of Malthus's intellectual heirs to believe, or at least hope —along with their more idealistic adversaries— that humans may be able to take control of their destiny. They shrink from the implications of their own arguments —as Malthus had done— and with better reason. For in Malthus's view, the primary consequence of the tendency for population to grow to the limits imposed by means of subsistence was poverty, and acknowledging human limitations meant accepting the inevitability of poverty in human society. But today, the apparent consequence of the tendency for population to grow at the expense of its means of subsistence is an impending disaster of such unimaginable proportions that few are willing to accept its inevitability. Almost everyone urges measures to avert the crisis--although strategies differ. And whether human beings can, in fact, take such control of their destiny remains to be seen.
