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The Logical Structure of Malthusianism

Malthusianism is more than simply a theory about the social interaction effects of population dynamics and food production. Logically speaking, it is the study of how different functions, which are all essential to social production and reproduction, enable and constrain each other. In abstract formal terms, this logical structure can be visually expressed by the following general scheme (Fig. 4.2).

At the heart of the model, there are two functions which are both vital to social production and reproduction. The first function (ƒ1) outpaces and strains the second one (ƒ2). For a while, this is obfuscated by the fact that time lags built into the system enable a temporary overshoot. In the long run, however, there is an inexorable mechanism by which the second function (ƒ2) constrains the first one (ƒ1). The way the mechanism operates is that the decline of ƒ2 leads to significant problems, which at the end of the day disrupt the unsustainable growth of ƒ1.

As we have seen, in classical Malthusianism population growth (ƒ1) outpaces and strains food supply (ƒ2) because the former function is exponential while the latter is only linear. Overshoot is possible for a while, for example due to a series of good harvests. In the long run, however, food supply (ƒ2) inexorably constrains population growth (ƒ1) because caloric intake per capita cannot fall below subsistence level. Famine and other calamities are then unavoidable. According to Malthus, “vice and misery” will ultimately bring population levels down.

Fig. 4.2 The logical structure of Malthusianism

Why Malthus Was Wrong

The theory is axiomatically true if one assumes, with Malthus, that the growth of food production is at best linear while population growth is inherently exponential. Or, more mildly, if one assumes that population growth outpaces but is ultimately constrained by the means of subsistence. Quite obviously, this is not how modern history has unfolded. So far, overpopulation has neither led to mass starvation nor to planetary pandemics or other forms of catastrophic rebalancing.

With hindsight, there are four reasons why Malthus has not been vindicated. First, his assumption of exponential population growth was largely correct at the time but is less so today. As a result of the so-called demographic transition, world population is moving away from familiar patterns of exponential growth. It is still projected to grow by another two billion people, from around seven billion in 2011 to about nine billion in 2050. But, at the same time, population growth has started to level off in most parts of the world (Lutz and Samir 2010; UN 2011).

Second, growth in food production has been far more than linear. Since the nineteenth century, industrial inputs such as chemical fertilizer and motorized machinery have dramatically intensified agricultural productivity. Thanks to an abundant supply of such inputs, food production has been largely able to keep pace with population growth. For the last couple of centuries, agricultural innovation has eluded Malthusian predictions over and over again (Trewavas 2002).

Third, globalization has enabled an unprecedented growth of both world population and food production. In line with circumstances in the early modern period, Malthus saw population levels as constrained by food production at the local level. Over the last two centuries, however, mobility and trade have shifted the territorial frame of reference first from the local to the national level, then to the international, and finally to the global level. To begin with, Europeans were able to move to “underpopulated” landmasses such as America and Siberia and to import raw materials and foodstuffs from the colonies. Subsequently the globalization of trade, and more recently of aid, has had similar effects, although in the reverse direction, buttressing indigenous population levels in developing countries.

Fourth, vulgar forms of Malthusianism tend to assume that any given resource base can sustain only a fixed number of individuals of some species, commonly called carrying capacity. For example, wild deer can for some time overgraze the available herbs on an island, but their population level will inevitably be adjusted downward to carrying capacity after a period of overshoot. While this notion of carrying capacity is suitable for simple cases of population biology, for example algal growth constrained by the surface of a lake, it is far too static for the study of more complex constellations.[1] When applied to human populations, carrying capacity can only be understood as a dynamic cultural concept, depending inter alia on technological innovation and social choice (Cohen 1995; Seidl and Tisdell 1999). The carrying capacity for irrigation agriculture is higher than for rain-fed agriculture, and the carrying capacity for a population of vegans riding on bicycles is higher than for a population of meat lovers driving about in SUVs.

  • [1] Even in the case of wild deer, overshoot may lead to a lowering of overall carrying capacity due to various forms of ecological damage. For example, after a cycle of overgrazing an island may be able to sustain fewer deer than previously
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