The concern on the natural resources shortage, caused by the population growth, has undoubtedly been the main debate topic historically discussed within the matter of the population-environment relationships. As we are going to see in the next section, nowadays, this topic is still current, to a certain extent.
The issue was firstly set out by Thomas Robert Malthus (1798), whose theory states that ‘the power of population is indefinitely greater than the power in the earth to produce subsistence for man’, i.e. the population growth is superior to the Earth’s capacity of natural resources production (especially food supply), since the first value grows geometrically and the second one, arithmetically. The consequences of this fact are the hunger and the mortality increase, and also the marriage delaying and the family size reduction. All of them contribute to the demographic growth slowing down. However, Malthus’s theory, which has been developed before the agricultural revolution, has received many criticisms, and the major one states that the theory is based on the belief that the natural resources production and also the land are steady, without taking into account the technological advances derived from the development.
In spite of the criticisms, the Malthusian theory had a large influence on the posterior studies, as it has been the start point of the carrying capacity concept development
David Ricardo, as Malthus, is concerned about the population growth, but he extends his analysis to all the resources, not only to land’s one. However, he states that the problem is not the finiteness of the resources, but the variability of their quality and location; and that these aspects are the responsible for the differential use of the resources and their relative shortage. Then, each author considers the resources shortage issue in a different way: whereas from the Malthusian viewpoint the shortage is seen as an absolute lack, caused by the finiteness and the homogeneity of the resources, from the Ricardo’s perspective, the shortage is relative and it is the result of the differential availability of resources, in terms of quality and location.
The second point of view is also upheld by the John Stuart Mill, who inserted an external conditioning factor to the demographic dynamics itself, which he has called the ‘civilisation progress’. This factor means the incorporation of the technologic changes (the agricultural knowledge and technologies, the insertion of new food, etc) as the essential aspect for avoiding the shortage. Therefore, it is the first attempt to break the linearity of both previous theories that characterised by the continuity of the processes and the phenomena, and the absence of changes or qualitative oscillations.
Karl Marx has also theorised on the relationships between the population and the natural resources and has criticised the Malthusian ideas, by arguing that if the society enters a steady state or a system crisis, the socioeconomic problems would be the main cause, not the existence of absolute physical limits, decreasing yields, or exponential population growth. According to Marx, Malthus was, more than a scientist, a representative of his social class, so his arguments were intended to justify certain economic and social measures. Regarding the overpopulation, Marx states that it is a ‘necessity’ of the capitalist system and also the result of its expansionist nature. Thus, according to Marx, the population cannot be considered as a variable external from the economic and productive system itself, nor as a parameter, but as an internal variable, whose trajectory and dynamics depend on the production forms.
There is another ‘classic’ contribution, made much more later by Ester Boserup, that has had a great influence on the posterior studies. As she has worked on it after the agricultural and the industrial revolution, Boserup suggests that the population growth and the subsequent density increase impulse the technologic changes, such as the use of ploughing or fertilisers, which allow the restoration of the balance between the food production and the population growth. Boserup’s ideas have made a great impact on the global and the regional scale investigation on the relationships between the population growth and the agricultural production changes in developing regions, above all. An example of this fact is the Matthew Lockwood’s study about the African continent, which states that the high demographic growth stimulates the investigation on new technologies and new resources. However, this investigation trend is broken in those countries which are suffering from poverty, war and overexploitation.