Why civilisations collapse

A study identifies over-exploitation of natural resources and economic disparity as two factors causing the collapse of civilisations and says the modern civilisation too is similarly vulnerable.

The Roman Empire is a prime example of societies that reached very advanced levels of civilisation only to end in an abrupt and precipitous collapse, which lasted for centuries. Seen here is the arch of Caracalla, one of the relics of the Roman Empire, in the town of Djemila in Algeria.

IS the modern civilisation susceptible to collapse just like many other civilisations, even advanced ones, that have collapsed over millennia? Yes, says a team of American researchers led by Safa Motesharrei of the University of Maryland and the National Socio-Environmental Synthesis Centre (SESYNC), United States, on the basis of a study using a simple mathematical model to describe the evolution of societies with differing patterns of production, consumption and distribution of resources among the people.

In a paper titled “Modelling Inequality and Use of Resources in the Collapse or Sustainability of Societies”, the researchers use a modified “predator-prey” model applicable to humans and nature that takes into account accumulated wealth and economic inequality in societies and conclude from an analysis of historical collapses that the phenomenon of collapse is ubiquitous. The collapse can also be irreversible in cases where the society makes a certain choice of production, consumption and distribution pattern. The work is due for publication in the May issue of the peer-reviewed journal Ecological Economics .

While there are widespread concerns that the currently evident population and resource-use trends are unsustainable, the possibility that this could lead to an overshoot, or even a collapse, has been controversial, they point out. According to their findings, however, modern civilisation too is susceptible, contrary to the widely held belief that modern civilisation, armed with its greater technological capacity, scientific knowledge and energy resources, will be able to survive and endure whatever crises historical societies succumbed to.

Recurrent phenomenon

However, the measure of this susceptibility is dependent on the nature of the society in terms of the extent of economic stratification, or inequality among the people. The study finds that, in broad terms, collapse can be avoided, and the population can reach a steady state at maximum “carrying capacity”, if the rate of depletion of nature is reduced to a sustainable level and if resources are distributed equitably. “Carrying capacity” is defined as the population that can be indefinitely sustained by a given environment. In history, there are many examples of societies that reached very advanced levels of civilisation only to end in an abrupt and precipitous collapse, which lasted for centuries. A well-known example is the Roman Empire’s dramatic collapse, followed by many centuries of population decline, economic deterioration, intellectual regression and disappearance of literacy. Similarly, the history of Mesopotamia, considered the very cradle of civilisation beginning around 3100 B.C., witnessed a series of rises and declines. In the Indian subcontinent, one can cite the examples of the Indus Valley Civilisation (3300-1600 B.C.) and the advanced civilisations during the Mauryan and the Gupta empires. The total disappearance of the Mayan civilisation presents a striking example. Similar episodes of civilisational collapse have occurred in other parts of the world as well.

A 2013 study of the collapses during the Neolithic period by Stephen Shennan and associates in Nature Communications , which the authors of the present study refer to, found that most regions showed more than one “boom-bust” pattern and population decline of 30-60 per cent. The timing and evidence suggest endogenous causes for the collapse rather than climate change or disease. These episodes also show a periodicity of about 300-500 years for such “boom-bust” cycles. “Despite the common impression that societal collapse is rare, or even largely fictional, the picture that emerges is of a process recurrent in history, and global in its distribution,” the paper says.

Noting that a large number of explanations have been proposed for each specific case, such as natural disasters, changes in the course of rivers, soil degradation, deforestation, climate change, tribal migrations, foreign invasions, changes in technology, changes in the methods or weapons of warfare, popular uprisings and civil wars, the authors say that these explanations are specific to each particular case rather than being general. They further point out that, even for a specific case where the explanation may apply, usually the society in question had already experienced the cause identified without collapsing. For example, many societies experience natural calamities such as floods, volcanoes and deforestation without undergoing a total disruption.

Posing the question “but why did this particular instance of this cause produce the collapse?”, the authors say that other processes, such as political, economic, ecological and technological, which have varied widely over a period in the collapsed societies, would have played a role. By modelling collapse mathematically in a more general way, the authors have attempted to arrive at a more universal explanation for this process.

The model, called Human And Nature DYnamics (HANDY), is, as mentioned before, based on the conventional predator-prey model used to study the biological dynamics of animal populations, typically two antagonistic species, which was changed to include two important elements that characterise human societies. In HANDY, the human population is the “predator” and nature (the surrounding environmental resources) is taken as the “prey”, which is depleted by human exploitation and consumption.

As the authors explain, the two distinguishing characteristics arise from the following considerations.

In the context of human societies, the population does not necessarily begin to decline once the threshold “carrying capacity” is crossed. Humans, unlike animals, can accumulate large surpluses and then draw upon this accumulated wealth when production can no longer meet consumption demands, thus introducing a certain delay in the cause-effect relationship. However, this accumulated wealth is usually not equitably distributed throughout society but is controlled by an elite class. There is an economic stratification in the functioning of society. As the authors note, the mass of the population, which actually produces the wealth, is allocated only a small proportion by the elites, usually at or just above subsistence levels. Separating the population into “elites” and “commoners”, the authors introduce a two-class structure in the model. The HANDY model thus consists of four equations for evolution, two for each class, as against two in the usual predator-prey model of animal behaviour.

Arguing against the widely held view that technological change can reduce resource depletion and thus increase the carrying capacity, the authors point out that the effects of technological change on resource use are not unidirectional. “Technological change,” says the paper, “can raise the efficiency of resource use, but it also tends to raise both per capita resource consumption and the scale of resource extraction so that, in the absence of policy effects, the increase in consumption often compensates for the increased efficiency of resource use.” They note that, in general, rather than increase the carrying capacity, this tends to reduce it. In the model, however, they assume that these two opposing trends cancel each other out.

The proposed model, the paper says, is not intended to describe actual individual cases, but rather to provide a general framework that allows carrying out “thought experiments” for the phenomenon of collapse and to test changes that would avoid it. “HANDY is not a forecasting model,” Motesharrei was quoted in an April 2 press release. “It cannot be used to predict the future of any society. It can, however, help us understand the possible underlying mechanisms in the evolution of a society.”

Three scenarios

Within this model framework, the authors study three typical scenarios: 1. Egalitarian society, which has no elites; 2. Equitable society, with a two-class structure of workers and non-workers but who are paid equally and consume at equal level; and 3. Unequal society, with elites and commoners, with the former consuming more than the latter.

The authors note that the scenarios that reflect the world today are represented by the runs of the model under category 3. “Under such conditions,” says the paper, “collapse is difficult to avoid, which helps to explain why economic stratification is one of the elements consistently found in past collapsed societies.” The authors find that for one choice of parameters, with optimal depletion and starting with a small number of elites, the society appears to be initially on a sustainable path for a long time. Eventually, however, the elites consume too much, resulting in a famine among commoners, leading to a societal collapse. This they call a Type-L collapse, which is due to an inequality-induced famine that causes a loss of labour rather than a collapse of nature.

With a larger depletion rate, the commoners disappear faster than the elites, who continue to thrive for a while and collapse later. “The buffer of wealth allows elites to continue ‘business as usual’ despite the impending catastrophe,” the paper says and suggests that this type of collapse, with a long, apparently sustainable trajectory, characterises the collapse of the Roman and Mayan civilisations. To avoid this catastrophic outcome in the unequal society scenario, the model runs suggest that inequality must be greatly reduced and population growth must be maintained below critical levels.

In the case of an egalitarian society (category 1), the study found that in the absence of elites if the consumption per capita is at an optimum level, the population grows smoothly and attains its maximum carrying capacity asymptotically. This results in a “soft-landing” to equilibrium with maximum sustainable population and production levels. A small increase in the depletion factor causes the population to overshoot its carrying capacity, but the overshoot being small (of the order of the carrying capacity), the system experiences small collapses that causes it to oscillate and eventually converge to a sustainable equilibrium with lower carrying capacity.

A greater increase in consumption makes the system experience oscillatory periods of growth, very large overshoots and major collapses that almost wipe out the population (Type-L collapse), but there is an eventual recovery of nature that allows the cycle to be repeated. Increasing the depletion factor further causes a complete collapse of the society, from which there is no recovery because there is an exhaustion of both labour and nature (Type-N collapse), indicating that if the depletion is large enough it can lead to a catastrophe even in the absence of economic stratification. The set of scenarios considered for equitable society (no economic stratification) leads to situations very similar to the egalitarian case depending on how high the depletion factor is.

The HANDY model, with economic stratification as an important parametric input, differs significantly from the pure predator-prey type models used in the study of evolutionary dynamics of human populations, which tend to show that while with a slow-growing resource base societies will exhibit overshoots and collapses, a society with a more rapidly growing resource base will result in an adjustment of population and resources towards equilibrium. The present model seems to represent historical collapses more accurately.

The results of the HANDY model experiments thus show that either one of the two features apparent in historical collapses—over-exploitation of natural resources and economic disparity—can independently result in complete collapse. If there is economic stratification, collapse is difficult to avoid. But if consumption is reduced to a sustainable level or if the resources are distributed equitably, the society can still attain equilibrium. However, even in the absence of economic stratification, collapse can still occur if depletion per capita is too high.

“The results of our model are optimistic, because they show that by making certain decisions, we can bring about a sustainable future,” said Jorge Rivas, a co-author of the paper. “Unlike physical and natural systems, we can, as humans, make critical choices that can change the long-term path that our social system will take, and we can optimise such choices using scientific models. This is a key takeaway lesson of this paper.”