Long Trends—Disease and Malthusian Cycles

Long Trends—Disease and Malthusian Cycles

Lecture 35

Tribute-taking states, we’ve seen, could encourage growth in several ways, but they could also discourage it. So, their overall impact on growth was rather contradictory. They sti ed growth in many subtle and not-so-subtle ways.

The previous lecture described some of the ways in which Agrarian civilizations could stimulate innovation. Yet if this is true, why were rates of innovation so much slower than in the modern world? Why were there such regular famines, and why did entire civilizations seem periodically to collapse? We will see that sometimes the same features that stimulated growth and innovation could also act as checks to growth. These factors help explain why ancient society did not show the productive dynamism of the most productive of modern societies. Exploring these features will eventually help us to better appreciate some of the distinctive features of the Modern era.

Because we have been focusing on long-term trends, we have focused on growth. But at smaller scales, and to thoughtful contemporaries, what stood out more sharply was a pattern of rise and fall that made history seem cyclical rather than directional. Peasants, too, were more aware of the cycles of the seasons and of years of feast and famine than of the long-term trend toward growth. Why did growth in this era always seem to be followed by collapse? Two main types of collapse stand out: political collapse (such as the decline of the Roman Empire) and demographic collapse (such as the Black Death), and often the two went hand in hand.

Shelley’s poem Ozymandias, written in 1817, provides a powerful symbol of political decline. As it happens, we know more or less who “Ozymandias” was. Shelley wrote his poem after hearing of the imminent arrival in the British Museum of a bust of Pharaoh Ramses II, “The Great,” who ruled Egypt for much of the 13th century B.C.E. What factors tended to undermine the power of rulers such as Ramses?

There is also a demographic oddity about this era. We have seen that, despite improved forms of agriculture and irrigation, populations grew no faster in the later Agrarian era than in the early Agrarian era. Indeed, in the 1st millennium C.E. there appears to have been hardly any growth at all in Afro-Eurasia. What factors checked There was plenty of innovation population growth? in this era, but it was never One of the curiosities of the later rapid enough to keep pace Agrarian era is that the same factors with population growth. that stimulated innovation could also check growth. The political structures of tribute-taking states could certainly encourage growth in some areas, but they also sti ed growth in many subtle and not-so-subtle ways. Normally, tribute-taking rulers were more interested in capturing wealth than in producing it. A successful war could generate wealth much more quickly than investment in infrastructure. Seeing themselves as capturers rather than producers of wealth, tribute-taking elites generally despised producers and merchants and took limited interest in how goods were produced and traded. Such activities discouraged policies that actively supported production and commerce. The structures of tributary power also sti ed growth in subtler ways. As Marx pointed out, tribute-taking states had to ensure that peasants had access to land. However, this limited wage-earning employment. It also deprived peasants of any incentive to raise productivity, as they knew that any surpluses would be skimmed by their overlords. In summary, those who produced society’s wealth generally lacked the education, the capital, and the incentive to innovate; while the elites, who had the education and the wealth, generally despised productive or commercial activities and preferred to take wealth rather than to generate it. Outside the specialist domains of warfare and administration, tribute-taking rulers took little interest in improved ef ciency or innovation. Patterns of disease frequently checked population growth. Two factors stand out, both closely linked to factors that, in other ways, could stimulate growth. While cities could stimulate growth by encouraging commerce, they could also sti e demographic growth (itself a key driver of growth, as we have seen) by creating lethal disease environments, so urban populations had to

be constantly replenished by immigration from rural areas. Diseases spread rapidly in lthy city streets; human and animal wastes accumulated in public places and waterways; rivers were treated as sewers and dumps; and city air was often polluted by res and manufacturing processes such as smelting or tanning. The expansion of exchange networks, another important driver of growth in this era, also encouraged the spread of disease. As William McNeill showed in his classic study Plagues and Peoples, diseases spread along trade routes, along with goods and ideas. As exchange networks expanded, they spread diseases to new regions. Indeed, he argues that both the Roman and Han empires may have declined, in part, because of the spread of devastating plagues along Eurasia’s expanding trade routes.

While humans are very good at nding new ways of exploiting their environments, they are not as good at identifying the limits of ecological exploitation. Time and again, Agrarian civilizations grew so rapidly that they began to overuse their forests, their rivers, and their crop lands to the point where entire civilizations collapsed. Estimates of populations in Mesopotamia over 7,000 years show two periods of sudden decline. The sudden collapse early in the 2nd millennium B.C.E. was almost certainly caused by overirrigation leading to salination and declining harvests. According to one estimate, Mesopotamian populations fell from over 600,000 in 1900 B.C.E. to about 270,000 by 1600 B.C.E., not to rise again for at least a millennium. A similar pattern of growth and decline would be repeated again early in the second millennium C.E.

These and other factors meant that, alongside the positive feedback cycles that drove innovation and growth, there were also negative feedback cycles that inhibited growth. This balance shaped the fundamental rhythms of historical change throughout the later Agrarian era. A typical cycle began with innovations that stimulated population growth, which in turn stimulated growth in other sectors. Eventually, though, populations began to press against ecological constraints. Shortages appeared, as did growing evidence of malnutrition, which encouraged disease. States increasingly began to ght over scarce resources; and nally, through warfare, disease, or famine, populations crashed. These rhythms are very clear on a graph of Eurasian populations over the last 2,000 years.

We will call these rhythms, which dominate the history of the later Agrarian era, “Malthusian cycles.” Thomas Malthus was one of the pioneers of modern demography. He argued that in all species, populations tend to grow geometrically while resources tend to grow arithmetically. Eventually, this means that population growth is bound to outstrip the available resources, leading to disease, famine, and demographic collapse. Economic historian Robert Lopez describes these cycles as “an alternation of crest, trough and crest … [that] can be observed not only in the economic eld, but in almost every aspect of life” (Christian, Maps of Time, p. 309). As French historian Le Roy Ladurie puts it, these cycles were like the “respiration,” the in-breaths and out-breaths, of an entire social structure (Christian, Maps of Time, p. 309). Explaining these cycles takes us to the heart of the issue of innovation in Agrarian civilizations. There was plenty of innovation in this era, but it was never rapid enough to keep pace with population growth. This fundamental fact explains the persistence of Malthusian cycles over several millennia despite a long term tendency toward growth throughout the later Agrarian era.

We have seen that in the later Agrarian era many of Rameses, Egyptian ruler for much of the 13th the factors that stimulated century, built this tomb, Ramesseum, for growth in some ways could himself outside of Thebes. also inhibit or help to sti e growth and innovation. This balance of forces that encouraged and sti ed growth explains why, eventually, each phase of expansion ended in collapse. In the last three lectures we have concentrated on Afro-Eurasia. But how typical was the history of the Afro-Eurasian zone of humanity as a whole? To answer that question we shift our focus to the Australasian, Paci c, and American world zones and ask what was happening there.

Corel Stock Photo Library.

Essential Reading

Supplementary Reading

Questions to Consider

Christian, Maps of Time, chap. 10. Fernandez-Armesto, The World, chaps. 4, 8, 14.

Mann, 1491. McNeill, Plagues and Peoples.

1. What forces inhibited innovation in the era of Agrarian civilizations?

2. Why did Malthusian cycles play such a dominant role in the history of all Agrarian civilizations?