The Black Plague

Michael Ahn

When considering the history of the world in which civilizations were developing all throughout Medieval Europe, one event stands alone among great catastrophes to have threatened the very viability of Western civilization and therefore marked a significant acceleration in the course of human culture.  Between 1347 and 1353, the Black Death had decimated a third of the European population from 75 million to 50 million and claimed nearly 200 million lives worldwide.  Paul Ehrlich describes history as a delicate interplay between minor microevolutionary forces, the behaviors and actions of individuals, and huge cultural macroevolutions, “the shaping of cultural trajectories by environmental factors”.  These forces influence societies of developing cultures and enter a feedback loop to steer further cultural evolution, not excluding mass death and epidemics.  The Black Death is a prime example of a pandemic collision between tremendous cultural macroevolutions driven by large scale circumstantial environmental factors and the microevolutions of human endeavors and symbolizes a pivotal moment for all European institutions of the Medieval Ages. 
            One of the characteristics that made the Black Death so deadly was the complete mystery about its pathogenic origin and principle perpetrator, a question still being asked today.  Since its discovery in 1894 by French bacteriologist Alexandre Yersin during the plague epidemic in Hong Kong, the bacterium Yersinia pestis has been generally accepted as the primary cause of the Black Death (although recent studies suggest a viral hemorrhagic fever infected Europe based on incubation accounts and genetic bottlenecking in Caucasians).  Y. pestis can take the form of three plagues, pneumonic, septicemic and the most notorious bubonic, and its natural vector is the parasitic oriental rat flea, Xenopsylla cheopis, transmitting the disease during its blood meal to its host, rat or human.  While the story about the emergence of the plague is well-known, in which black rats, Rattus rattus, infested with diseased fleas travel on merchant ships from Central Asian ports to European countries, the remarkable ability of the plague to spread and kill inhabitants so quickly and efficiently requires a more nuanced story. 
            Once the rats-covered-in-fleas-infested-with-plague reached the ports of Italy in 1346, the plague met very little resistance to its eruption.  Using Jared Diamond’s perspective from the microbial point of view, Medieval European societies were the perfect breeding grounds for the plague.  Not only did the economic centers and trading hubs of large ports provide the routes and transportation between cities to spread geographically, the constrained cities in those ports with high density populations allowed for rapid transmission among humans.  Rats ran rampant in the underdeveloped sewage and sanitation systems, swiftly reproducing and invading every corner of cities and towns.  And at the same time, it has been speculated that rats met little ecological predation due to the mass extermination of cats during the Middle Ages for their association with witchcraft and Satanism, a tragic belief exacerbating the epidemic and one of many factors fueled by the Christian institution.  While the rats were multiplying, the fleas were also multiplying, jumping from rat hosts to human hosts and laying eggs wherever humans and rats inhabited.  The scarcity of baths and lack of pest control may have also intensified the proliferation of fleas. 
            The disease itself was facing a much weakened and highly unprepared population due to harsh environmental factors, the products of which persisted in the feedback loop of human destruction.  Prior to the plague outbreak, the Great Famine of 1315-1317 had marked the end of the prosperous High Middle Ages with the deaths of millions and its lasting consequences.  Europe was very susceptible to food shortages because of the slightly changing climate during this time and the difficulty in clearing the clay-soil for agriculture.  Continual bad weather consisting of severe cold and wet winters led to numberous food shortage sand placed the laboring population in a perpetual cycle of hunger, malnutrition, and pestilence.  Productivity of laborers was at a low with reduced grain harvests, causing supply prices to rise and further choking the already abysmal standard of living.  Limited diets and nutrition led to more deaths and lower productivity and paved the way for epidemics even before the Black Death, such as typhoid and possibly anthrax, which may have killed crucial domestic animals.  What the plague was confronting during the middle of the 14th century was an already devastated yet high population of weak laborers and an economic situation already stifled by food shortages and a dying working class; there almost was no cushion or buffer for the population to fall on. 
            As a result of yet another crisis, this time the Black Death, attacking European societies still recovering their pieces, there were major cultural upheavals in the realms of religion and science to ameliorate the morbidity brought by the Black Death.  The Catholic Church, being the dominant religion of the European continent, met the most extreme reactions towards a disease with no possible and physical cure existing on Earth at the time.  The silence of God had been heard since the Great Famine for unanswered prayers and pleas for mercy, and the inability of the church to perform basically miracles was nothing but a reason to repent for sins and wickedness.  Evolution undoubtedly accelerated within the supernatural and superstitious sect of human culture, which included the movement of flagellants (extremists who whip their bodies in repentance and punishment for the plague), the personification of Death and the Danse Macabre (Dance of Death), the persecution and purging of minorities, Jews, beggars, lepers and witches.  Alas, the desolate intellectuals who survived the plague would slowly turn towards empirical answers.
            Modern medicine has much to owe towards the effectiveness of such a deadly, painful and highly contagious disease for its existence as a life saving technology.  Early  Western medicine, like all doctrines of their time, was centered on traditional authority in which past assumptions are inexorably accepted and passed down through medical institutions, including monasterie,s and primarily based on herbalism, Greek humorism i.e. blood letting and mystical remedies.  Arising from the unanswered prayers from even the most devout came the gradual rejection of previous held Antique notions of diseases and the human body for more biologically based theories and evidence.  With questions asking biological systems come biological treatments and continual scientific innovations, but it would not be until the end of the 19th century that bacteria would be discovered as the causes of disease and therefore antibiotics would be produced (by Robert Koch and Paul Erhlich respectively). Modern medicine took centuries to gain momentum in technological advancement and scientific prestige, slower than other fields of science, only after the centuries of indoctrinated religious fabrications about disease finally dissolved.  Diseases were believed to be God-sent punishments and divine scourges and so medicine was not considered a suitable profession for devout Christians to delve in, rather divine recovery through mercy and repentance seemed like the obvious remedy. For example, had monks and nuns known that the septicemic plague was transmittable even through the breath perhaps they could have prevented the contagious spread among their devout followers and the sickly they tended for.
            The feudal system, however, remained unchanged throughout the wake of the Black Death’s destruction largely due to key agricultural advances in efficiency.  Despite quickly dwindling serf and peasant populations, the agricultural improvements such as the iron plow (for easier tilling and churning of the hard soil), the three-field crop rotation system (instead of two-field), fertilization with manure (to restore depleted nitrogen in the soil) allowed crippled kingdoms and societies to limp on towards recovery. Had it not been for these innovations, the population may have arguably continued its plummet towards its own extinction or until the disease finally died out (which it miraculously did) and the environment was able to sustain an increasing carrying capacity (which these innovations helped to achieve).
            An issue among debate about the Black Death was whether such a catastrophe was inevitable given the immense growth of the global population during the Early and High Middle Ages (5th -14th Century).  Were the population’s subsistence demands exhausting the agricultural supplies produced by the heavily transformed environment through depleted soil nutrients and overpopulation?  Dubbed the Malthusian Crisis, this perspective views the plague as an inevitable “reckoning” or corrective measure instigated once reproduction levels had surpassed the limitations of food supply.  It may be easy to jump to this conclusion by only looking at the statistics during the Black Death years and claim that the plague controlled the population and carrying capacity in check with each other, but the events preceding the epidemic would suggest otherwise.  The series of famines starving the overpopulated lands for the decades before the plague seem to be the more direct and plausible reaction of an environment stretched beyond its bounds rather than an infectious biological weapon sent by mother nature At the same time, the onslaught of the famines could be traced back to the changing climates; if weather had been permitting could have the population continue to grow at least until the Industrial Revolution in which technological innovations liberated men from the Malthusian constraints? Perhaps after the climate change, man and nature were actually stuck in a long stalemate when famines capped the productivity of the land and reproduction of humans while men drained every grain of wheat possible to sustain themselves and that this was the fragile carrying capacity of the European environment before the plague tipped it over the ledge.  Thus, was the Black Death truly inevitable considering the unpredictable (at that time) climate changes which may have induced this feed-back loop operating in slow yet destructive manners before culminating in a drastic climax of mass death? 
             Whether through Malthusian inevitability or natural serendipity, one thing is for sure: the conditions were perfect for the Black Death to strike.  The successes of the plague surfaced the glaring failures of humans and civilizations in virtually all realms of culture and technology leading to important improvements taken for granted today in: sanitation, medicine, architecture, agriculture, pest control, and religion.  For such an iconic Medieval cornerstone inscribed with the story of rats on merchant ships and decimated towns, the history of the Black Death can be seen as an amalgamation of ongoing macroevolutionary and unrelated microevolutionary forces setting the stage for a devastating but necessary epidemic that truly changed the world.


Ehrlich, Paul. Human Natures: Genes, Cultures, and the Human Prospect. “Gods, Dive-Bombers, and Bureacracy.” Island Press, Washington D.C. 2000

Diamond, Jared. Guns, Germs, and Steel. “Lethal Gift of Livestock.” Springer, New York. 2005

Williams, Michael.  Deforesting the Earth: From Prehistory to Global Crisis. “The Medieval World.”. Chicago: University of Chicago Press, 2003.

Lavelle, Peter. “On the Trail of the Black Death”, News in Science. ABC Television. Published online 2004

Kelly, J. The Great Mortality, An Intimate History of the Black Death, the Most Devastating Plague of All Time. Harper Collins, New York. 2005

J. M. Bennett and C. W. Hollister, Medieval Europe: A Short History. McGraw-Hill, New York.  2006


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