Pathogenesis: A History of the World in Eight Plagues

by Jonathan Kennedy

A retrovirus is a specific type of virus that reproduces by inserting a copy of its DNA into the genome of the host cell. But when a retrovirus infects a sperm or egg cell, something remarkable happens: viral DNA is then passed on to every cell in every subsequent generation. An astonishing 8 percent of

pathogenesis refers to the origins and development (genesis or γένεσις) of a disease (pathos or πάθος), with a particular focus on the way that pathogens infect our cells and the effect this has on our bodies. In the pages that follow, we will explore how viruses, bacteria and other microbes impact aggregations of bodies—that is, the body politic, body economic and body social.

we will explore the role that billions or trillions of microscopic viruses and bacteria have played in history.

pathogens have been the protagonists in many of the most important social, political and economic transformations in history:

By the time we have finished, I hope to have changed the way you think about history and our species’ role in it—to convince you that the modern world has been shaped by microbes as much as by women and men.

Tibetans carry a Denisovan gene mutation that affects red blood cells, making it possible to live comfortably on a 13,000-feet- or 4,000-meter-high plateau

The Inuit of northern Canada and parts of Greenland and Alaska have retained Denisovan genes that influence the storage of fats, which helps them to thrive in an exceptionally cold climate.

The vast majority of pathogens that are capable of infecting humans are zoonotic—that is, they originate in animals and then jump the species barrier to infect us.

Our ancestors traveled deep into Eurasia, where they encountered Neanderthal and Denisovan communities that had never been exposed to African pathogens and hadn’t had the opportunity to build up any tolerance. Within a relatively short period of time all other human species died out and were replaced by the newly ubiquitous Homo sapiens.

To understand the potential impact of contact between Homo sapiens and Neanderthals, consider that Native Americans and Europeans had been separated for about 17,000 years before renewed contact literally decimated the indigenous population of the Americas in the sixteenth century. Modern humans and Neanderthals were separated for at least thirty times longer.

Prehistory was punctuated by massive waves of migration that resulted in a new population moving into a region and almost completely wiping out the previous inhabitants.

In addition to novel pathogens, Neolithic immigrants brought new genes, new languages and new ideas such as farming and metallurgy. In this way, plagues that occurred thousands of years ago played a crucial role in shaping the world we now inhabit.

Jared Diamond argued that the adoption of settled agriculture was the “worst mistake in the history of the human race.”[16]

Graeber and Wengrow argue that both of these grand theories oversimplify the argument. They assume that the adoption of settled agriculture—in particular cereal-farming and grain storage—led to the emergence of hierarchies and states. In the standard civilizational narrative this is the best thing that ever happened to our species; for Rousseau and Diamond it is the worst.

the impact of settled agriculture on infectious diseases is more straightforward to analyze.

Between 500 and 1,000 years after a community adopted settled agriculture we tend to see a marked increase in deaths, causing population growth to level off and, in some cases, go into reverse.[24] What caused this sharp rise in mortality? Part of the answer related to diet.

settled agriculturalists were much more likely to starve than hunter-gatherers.

the Neolithic diet was lacking in protein and vitamins. As a result, almost everywhere that humans adopted settled agriculture, early farmers were less healthy than hunter-gatherers. Their skeletons were shorter and more likely to show signs of anemia due to iron deficiency and enamel defects as a result of lack of vitamins A, C and D, calcium and phosphorus.

because humans’ exposure to pathogens increased markedly after the adoption of agriculture.

an epidemiological revolution followed hot on the heels of the Neolithic Revolution.

The most likely answer is that the farmers were unwittingly aided by pathogens that emerged after the Neolithic Revolution.

the hunter-gatherers that the Neolithic European Farmers encountered as they migrated westward through Europe would have been almost defenseless against these viruses and bacteria.

With the arrival of settled agriculture, the population of Europe boomed as women had more children and the men exploited the land more productively than the foraging population.

Hippocrates is referred to as the father of Western medicine because he pioneered clinical observation and the systematic classification of diseases that form the basis of modern medicine.

By 220 BCE Rome controlled all of the Italian Peninsula. It conquered most of Greece in 146 BCE, and the Hellenistic kingdoms followed. A much-reduced Seleucid Empire was swallowed by the Romans in 63 BCE; Cleopatra was the last Ptolemaic ruler of Egypt before it became a Roman province in 30 BCE.

infectious diseases played a vital role in both the demise of the Greco-Roman gods and the rise of two new religions: Christianity and Islam.

Even now, the water in the Trevi Fountain is supplied by an aqueduct dating from the first century CE.

Even the lauded baths were more of a danger than a benefit to public health. In Rome’s bigger institutions thousands upon thousands of people soaked in the same water every day.

Contemporary writers complained about the water being dirty and contaminated with human excrement. In other words, Roman baths created an ideal environment for waterborne diseases to spread.

The pax Romana produced conditions that were ideal for the emergence of epidemic infectious diseases. The growth of long-distance trade with sub-Saharan Africa, India and China increased the risk that Romans would come into contact with novel pathogens—and the well-connected, highly urbanized Roman Empire created a perfect breeding ground for fast-spreading new diseases.

Until recently, infectious diseases were largely ignored in mainstream accounts of the decline or transformation of the Roman Empire. But in his recent book The Fate of Rome, Kyle Harper gathers a large amount of evidence to show that a series of pandemics caused immense damage and played a crucial role in weakening the Roman Empire,

It wasn’t a coincidence that the two high points of repression coincided with the Antonine and Cyprianic Plagues. Pagans believed that the presence of a new religion was displeasing the Roman gods or driving them away, and therefore Christianity was responsible for the widespread death and disruption.

Christians looked after the ill during the Plague of Cyprian: “Heedless of danger, they took charge of the sick, attending to their every need.” Christians would have been able to reduce mortality by up to two-thirds just with basic nursing, such as providing food and water.[48]

The arrival of plague was a hammer blow to Justinian’s revitalized empire. The Byzantine writer Procopius, who witnessed the first wave of the epidemic, describes how “the whole human race came near to being annihilated.” He claims that 10,000 people died every day in Constantinople at its height.

A few decades after the plague first struck, the army totaled 150,000 and had difficulty mustering 10,000 soldiers to fight.[62] From the 560s onward, the Eastern Roman Empire once again began to lose the western provinces, which it had only just regained, to Barbarian invaders. The Lombards reduced the areas under Roman control in Italy, Slavs and Avars pushed into the Balkans, Visigoths conquered the Roman province of Hispania and Berbers captured much of the countryside in North Africa.

As wave after wave of disease struck Eastern Romans and Persians, the two empires became ever weaker. All the while, the Prophet Muhammad looked on with interest from Medina.

In the 630s and 640s, Muslim Arab armies swept across the wealthy and densely populated Roman provinces in the Middle East and North Africa. The holy city of Jerusalem was captured in 637. Alexandria, the great center of Greek culture, fell in 641. These territories would never be regained by the rulers in Constantinople, although they continued to control a much-reduced Byzantine Empire until 1453.

most subjects of the caliphate continued to follow Christianity and Zoroastrianism for several centuries.[69] Syria-Palestine didn’t become Muslim majority until the twelfth century, and Egypt not until the fourteenth.

The creation of the Arabian Empire was the result of a series of astonishing military victories against the plague-devastated Byzantines and Sasanians.

Belgian historian Henri Pirenne famously argued that without Muhammad, Charlemagne would be inconceivable.[73] The political vacuum in northwestern Europe ultimately led to the emergence of a new order that was dominated by a patchwork of small kingdoms, feudal lords and thriving city-states but was at the same time unified by its Christian identity, in opposition to its Muslim neighbors to the south and east.[74]

mortality rates from the Black Death were astonishingly uniform across the continent, and the medieval plague did not upend the power balance on the continent as it had done in antiquity—except in the southeast, which witnessed the remarkable rise of the Ottomans.[38]

it’s not possible to understand the seemingly miraculous Ottoman expansion unless we consider the impact of the Black Death.

The Black Death once again aided the Turks’ southern and eastern expansion. Egypt, the Levant and Syria were repeatedly devastated by the plague, as they were densely populated and well connected to Asia. The disruption appears to have been even greater than in Europe:

So many people had left property to the Church when they died that by the Middle Ages it owned about a third of all cultivated land in western Europe.[50]

So many clergy perished that the Church had no choice but to loosen the entry requirements in order to replace them, resulting in an influx of inexperienced and, in many cases, even more unsuitable people into the priesthood.

There had been challenges to the authority and teachings of the Catholic Church before, but these ideas had failed to gain widespread support until the Black Death. John Wycliffe, a priest and theologian based at Oxford University, was born in the 1320s and became a leading light in the rebellion against religious orthodoxy and Church corruption in the second half of the fourteenth century.

in the middle of the fifteenth century, Johannes Gutenberg invented the printing press. The increasing use of labor-saving devices was a direct response to the challenges created by the Black Death and subsequent outbreaks of the plague, because there were now so few workers that labor-intensive processes had become unviable.

The impact of the printing press on the spread of Protestantism was so important that Luther is said to have referred to it as “God’s highest and most extreme act of grace.”[61] The post–Black Death growth of universities also helped to promote a new intellectual spirit that laid the ground for the Reformation.

The Peace of Westphalia, which determined that each prince could choose his state’s religion, not only ended the conflict but also shattered the Catholic Church’s supreme spiritual authority.

was only in England that the post–Black Death conflict between the lords and peasants resulted in the demise of feudalism and the transition to capitalism.