Malthus's Message

At the end of the eighteenth century, Thomas Robert Malthus began the debate on the existence of a universally valid population principle or law. This was one of his contributions to the construction of the liberal (i.e., free market) economic theory. In the first edition of An Essay on the Principle of Population (1798), he highlighted the irreconcilable contrast between the arithmetic proportions of the growth of crops and the geometric growth of human beings, a famous statement that nevertheless is overly simplified. The historical starting point of the debate was the fact that the Europeans colonizing North America at Malthus's time doubled their numbers every 25 years. Although such dynamics cannot be found in many other times and places, Malthus's observation correctly underlined that resources are limited and are therefore not commensurate with the generative capacity of our species. This principle inspired both Darwin and Wallace to formulate the principle of natural selection. Beyond his mistaken representation, Malthus defined the principle of population as “the constant propensity of all living beings to multiply beyond what the available means of subsistence allow” (Malthus 1965, 3). In biology this is called r-selection strategy and it is typical of small organisms. Bigger species, in which procreation is more costly, developed a K-selection strategy that invests more in fewer offspring.

The Malthusian principle therefore advances the idea of a natural propulsion of the population to multiply if resources allow it, and also beyond that. Widely dubbed as “Malthusian,” the theory that the human population has a natural propulsion to grow until it reaches ecological limits, in particular that of food production, actually greatly simplifies Malthus's idea, as he also noted that “the population does invariably increase when the means of subsistence increases, unless this is prevented by some very powerful and evident constraints,” referred to as “moral restriction, vice and misery.”

Following Adam Smith and David Ricardo, Malthus developed his reflections on population trends in the economic law of diminishing returns. The law of diminishing returns states that the yields of a field can be improved with more work or capital (e.g., the purchase of fertilizers, deeper plowing by means of larger and heavier plows and irrigation), but any additional input of one of these “factors of production” (as they are called by free-market theorists) will give an additional yield that is lower and lower.