Germs, Genes, & Civilization: How Epidemics Shaped Who We Are Today
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How did disease affect the rise of Rome?
It has often been suggested that malaria played a significant part in the fall of the world’s greatest civilization, the Roman Empire. But before we deal with its fall, let’s consider some biological factors involved in the empire’s rise to greatness.
The Romans had two great virtues, discipline and pragmatism. The first contributed to the most effective military organization of ancient times. The second was expressed in their civil engineering. The Romans are remembered for their legions and their roads. But they also built a wide range of structures concerned with water: reservoirs, aqueducts, canals, irrigation channels, public baths, sewers, and many miles of water pipes.
Improved water engineering had two major biological effects. Better irrigation allowed the Romans to grow more food per acre and to support a greater population density. Moreover, by providing clean, fresh water and by building public baths and sewers, the Romans greatly reduced the impact of infections that are carried by contaminated water or human waste. Consequently, their population was healthier and they lost fewer victims to disease than their less hygienic competitors. More people meant more recruits for the legions. More soldiers meant more conquests and more land to irrigate. And so an upward spiral continued until other negative, biological factors limited it.
Increased population density is a biological factor that at first seems unfavorable. Consider a society that has progressed to crowding together a large number of people into growing cities that are significantly larger than neighboring communities, such as Babylon, Nineveh, Athens, or Rome. Any passing epidemic will spread more efficiently through the crowded city than in the towns and villages of more sparsely populated neighbors. Sooner or later, any such overcrowded city will be struck by pestilence. Its population will be decimated, and for a while it will be vulnerable. However, provided that it survives and recovers, its population will now consist of those who are resistant to the plague of the day. In other words, denser populations will be the first to evolve resistance to those infectious diseases that are current in their region of the world.
The next time a major conflict occurs, the movements of armies and of refugees will distribute any available infectious diseases around the war zone. The enemies of the big city-state, from smaller towns and villages, will have built up less resistance than the population of the largest city. Voilà! Infection will do most of the dirty work: The enemy will be devastated by whatever plague is in circulation, and the bigger city will gain a massive advantage. Cleanliness might be next to godliness, but the demons of disease fight on the side with the denser population.
But how can we have it both ways? First, not all diseases are spread by water or human waste, so improved hygiene from civil engineering still leaves plenty of scope for insect-borne scourges such as bubonic plague, typhus, or malaria, and for airborne diseases such as measles or smallpox. Second is the matter of temporal sequence—Rome was not built in a day. Early in its history, Rome was indeed struck by several epidemics whose nature is unknown to us because the records are fragmentary and give little clue to the symptoms. Though devastated, Rome pulled through.
Overall, a fine balance must be struck between the advantages of a disease-resistant population and a plentiful supply of healthy manpower. Consequently, great empires are few and far between. Nonetheless, when a major population center does gain a lead over its competitors, such biological factors make it extremely difficult to overthrow. Despite this, all good things eventually come to an end. As population density continues to grow, the pendulum swings back in favor of the spread of infectious disease. Sooner or later, the invisible legions of microorganisms make a comeback. In the case of Rome, this was much later and did not happen until the exhaustion of natural resources and resulting environmental damage gave infectious disease a helping hand.
How much did malaria contribute to the fall of Rome?
In ancient times, malaria was endemic in large areas of Italy, Greece, the Middle East, and North Africa, all of which were incorporated into the Roman Empire. Although we often think that ancient peoples had little idea of what caused disease, this is not entirely fair. Roman author Marcus Varro theorized that malaria was due to “tiny animalcules” that multiply in marshy places, float in the air, and sneak into people by the mouth and nose, causing fever and sickness. He was not wholly correct, yet he came close. Other Romans realized that the annoying insects that breed in marshes helped spread disease. Varro’s real problem was not so much ignorance as having no way of proving his assertion. More than a millennium later, Western technology developed microscopes capable of seeing Varro’s animalcules. And so those who thought that diseases were the result of God’s displeasure, night air, or vapors from decaying garbage often dominated public opinion.
Did malaria really promote the downfall of the Roman Empire? Granted, the Roman Empire took a heavy toll from malaria, but so did all other ancient cultures inhabiting the coastal regions of the Mediterranean basin. Unlike bubonic plague or smallpox, malaria does not occur in epidemics that sweep through a civilization, leaving massive casualties over a relatively brief time span. Malaria is an endemic disease and takes up permanent residence in an area whose inhabitants are, therefore, subjected to continuously recurring infections. The disease takes a continual heavy toll not only on life, but also on vigor. In areas where malaria is endemic, the heaviest casualties are among the newborn. Adults quite often survive the disease but are seriously debilitated and frequently fall ill again from recurrent attacks.
Evidence from corpses reveals that malaria has been present in the eastern Mediterranean region since Neolithic times. Typical Egyptian mummies had their abdominal organs removed. However, mummification was developed gradually, and some of the earliest Egyptian mummies, which date to before the abdominal organs were removed, have large swollen spleens, symptomatic of malaria. Sometime in the fifth century B.C., malaria arrived in Greece, and by the next century, it was the most common serious disease. During the fourth century B.C., malaria moved into the marshlands near Rome. The Romans responded by instituting the worship of Dea Febris (Goddess of Fever). In addition, the Romans began recruiting soldiers for the legions from mountain areas free of malaria.
Three main ecological factors worked together to undermine classical civilization: deforestation, soil erosion, and the formation of marshlands. Heating, cooking, and smelting metal ores all consumed large amounts of wood. The grazing of livestock, especially goats, prevented the regrowth of shrubs and trees, making matters worse. Although they planted olive groves and fruit trees, the Greeks and Romans made little attempt to replace the forests used for fuel. Consequently, the growing population of the Roman Empire destroyed the bulk of the Mediterranean forests. This, in turn, led to massive erosion of the soil on the exposed slopes. As upland areas became less fertile, productivity fell. The soil swept downstream by rivers was deposited in more level areas, especially around lakes and at river mouths. There it formed flat, poorly drained marshlands that allowed mosquitoes to breed, thus spreading malaria. Although alluvial deposits provide good, rich farmland, the presence of malaria drove away many of the farmers. Those who stayed suffered constant debilitating attacks. Malaria is almost never totally eliminated from the body, and exertion can bring on subsequent attacks. Those who stayed either avoided hard work because it triggered renewed bouts of malaria or worked hard and fell victim to further attacks. Either way, agricultural productivity declined.
The refugees, who left the land, fled to the cities, where they relied on the grain handouts the government provided to the urban poor—the famous “bread and circuses.” This problem was exacerbated by the land-reform policies of Roman populists such as Julius Caesar, who distributed land to retired legionaries with little experience in farming. By the time of the first emperors, Italy could no longer feed itself and Rome had become dependent on grain imported from the fertile Nile valley, which explains why controlling Egypt and No
rth Africa was of such critical importance to the Romans. Of course, the densely populated valley of the Nile was also the channel by which diseases emerging from sub-Saharan Africa found their way into the Roman Empire.
Uncivilized humans and unidentified diseases
The rising numbers of urban poor and the consequent overcrowding provided opportunity for the spread of epidemic diseases. These were not long in making an appearance. Several major epidemics struck the Roman Empire in the first half of the first millennium A.D. The identities of these diseases are uncertain, until the Great Plague of Justinian (540 A.D.), which was almost certainly bubonic plague. The succession of epidemics gradually depleted the manpower needed for both the legions and the economy. Eventually, the empire became too depopulated to defend itself.
Why is it so hard to be sure of the identity of ancient epidemics? One issue is that ancient writers were often more worried about the effects of the pestilence and its religious implications than in accurate scientific diagnosis. Less obvious is that many diseases change over time or even go extinct, as discussed in Chapter 3, “Transmission, Overcrowding, and Virulence.” Thus, even when described thoroughly, ancient plagues might be unrecognizable today. Despite this, historians often feel obliged to name the epidemic, almost always choosing a well-known modern disease.
For example, the first major epidemic to strike imperial Rome occurred in 79 A.D., just after the volcano Vesuvius erupted, and was largely confined to Italy. Guesses have included virulent malaria or anthrax. Neither makes any real sense. Recently, genuine evidence has come to light. Examination of bodies buried alive by the volcano has shown symptoms of brucellosis. Moreover, we know that the Romans used milk from sheep and goats without, of course, sterilizing it. Even today, various strains of Brucella, some virulent in humans, are found in sheep and goats and their milk and cheese.
The next was the plague of Orosius in 125 A.D. This started with a famine caused by locusts eating the crops in North Africa. The plague itself also began in North Africa and moved from there to Italy. The identity is uncertain. Whole villages and occasional towns were wiped out and abandoned.
The plague that started in the Middle East in 164 A.D. is named either after Antoninus, emperor when it began, or Galen the physician. Soldiers from Syria brought the disease back to Rome in 166 A.D. Corpses were removed from Rome by the cartload. The plague swept through the empire until 180 A.D. and, as a final blow, killed the emperor, Marcus Aurelius. After a brief respite, the plague returned in 189 A.D. This epidemic was the first to cause a break in the Roman defense perimeter. Before this, the empire continuously expanded and was able to hold its frontiers. In 161 A.D., a horde of Germanic barbarians, the Marcomanni, left Bohemia (now in the Czech Republic) and assaulted Italy from the northeast. Disruption from the epidemic left the Romans incapable of counterattacking until 169 A.D. Reports of the conflict suggest that most of the dead Marcomanni were actually killed by disease spread by the Roman legions.
The most famous physician of Roman times, Galen, fled from Rome during this plague. He also left a description of its symptoms. High fever, inflammation of the mouth, and diarrhea were followed by eruptions on the skin, although many died before this stage. One unproven and unlikely theory is that this was the first smallpox epidemic to hit the West. This hypothesis suggests that a smallpox outbreak in Mongolia set the Huns in motion. The Huns then both infected and displaced various Germanic tribes, who, in turn, infected the Romans. However, the Marcomanni apparently caught the plague from the Romans, not vice versa. Moreover, if the Huns and Germans had been decimated first, it is hard to see them applying much serious military pressure on their neighbors. Furthermore, the course of the epidemic does not resemble later, better-known European smallpox epidemics.
Next came the great plague of Cyprian in 250 A.D. Cyprian was the bishop of Carthage, in North Africa. He described violent diarrhea, vomiting, fever, ulcerated sore throat, and gangrene of the extremities. No rash or skin eruptions were noted, and the identity of the disease remains obscure. This was a true pandemic, spreading from Africa throughout the known world and lasting for some 16 years. It moved rapidly, both by person-to-person contact and on clothes or personal articles used by its victims. It was more virulent than previously recorded diseases, killing more than half of those who were infected. Panic followed pestilence, and refugees fleeing their homes spread the plague. Large areas of Italy were left uncultivated, and the empire was weakened by loss of manpower. By 275 A.D., the empire had retreated to the Rhine and the Danube, abandoning Transylvania and the Black Forest region. The emperor, Aurelian, took the unprecedented step of fortifying Rome itself.
Over the next couple centuries, successive epidemics, probably of the same disease, ravaged the Roman Empire. Barbarian attacks intensified, especially from the Goths and Vandals. A downward spiral of pestilence, famine, and war led to the decline and collapse of the Western part of the empire. Accurate records became few and far between as civilization fell apart. The collapse took longer than might have been expected because the Romans infected the incoming barbarians, whose hordes were thinned out by pestilence, too. In 447 A.D., Attila the Hun was approaching Byzantium, capital of the Eastern Roman Empire, when pestilence “of the bowels” (perhaps dysentery of some sort) broke out among his army. The Hun army was not destroyed, but the campaign was abandoned. In 452 A.D., as Attila approached Rome, there was a repeat performance and the Huns were halted by what was presumably the same disease.
Sometimes disease struck the barbarians after they had defeated the Romans. For example, the Vandals, who had taken control of Rome’s northern African territories, were so devastated by a plague in 480 A.D. that they were swept away by the Moors, a nomadic Arab people. In 539 A.D., the Goths and Byzantines were fighting for control of Italy when the Franks burst in, hoping to take advantage of the confusion. According to the Byzantine chronicler Procopius, the Franks succumbed to the Italian secret weapons: dysentery and diarrhea.
For those who like economic theories, we should point out that the two great plagues of 164 A.D. and 250 A.D. led to the collapse of the Roman fiscal system. As is usual, casualties from the epidemics were heaviest among the poor. The ratio of peasants and laborers declined relative to the upper classes. The colossal die-offs thus eroded the tax base. In an attempt to maintain public spending on roads, irrigation, and other public works, as well as pay the legions, taxation rates were increased. This led to poverty and destitution among the surviving lower orders. Malnutrition and poorer housing resulted, which raised susceptibility to infection. A downward spiral of overtaxation, epidemic infection, and underpopulation thus set in.
Bubonic plague makes an appearance
In the East, the Roman Empire developed into the Byzantine Empire, based on Byzantium (Constantinople). The Byzantines fantasized about retaking the Western territories, especially Rome itself. The emperor Justinian (527–565 A.D.) came closest. After successful wars on his other borders, he invaded the West in 532 A.D. He retook North Africa, Sicily, Italy, and even part of Spain. If merely human enemies had opposed him, Justinian would have probably succeeded. But just as he was preparing to invade Gaul, another foe emerged: bubonic plague.
Vague accounts suggest that bubonic plague might have afflicted the Egyptians, Philistines, and other Middle Eastern nations since 1,000 B.C. or earlier. However, Justinian’s plague was the first outbreak of bubonic plague described in sufficient detail that we are sure of its identity. To the physicians of Byzantium, it was a novel and terrifying disease. Desperate to understand its cause, they performed autopsies on some of the victims. They found what they called “anthraka,” the hardened remains of lymph nodes. Our word anthracite, a type of coal, comes from the same root and reminds us that bubonic plague was called the “Black Death” because the swellings turned into hard black lumps.
Fever was followed by the appearance of buboes, black swellings in the groin and armpits due to swollen lymph nodes. Death ty
pically occurred on the fifth day, sometimes sooner and sometimes later. Procopius, archivist to Justinian, correctly records that bubonic plague was not directly contagious and that outbreaks began on the coast. Today we know that bubonic plague is carried by fleas, which, in turn, are carried by rats. The rats spread from country to country by ship, so the plague spreads from the ports inland. Because infection is by fleabite, those who came in direct contact with plague victims were no more likely to be infected than others within range of the fleas.
The plague of Justinian began in 540 A.D. in Egypt. It spread through the Middle East and, from there, to the rest of the known world. It struck Byzantium itself in 542. As is typical for bubonic plague, the mortality was low at first and then rose steeply. The inhabitants of Byzantium died faster than graves could be dug for them. The towers of fortresses were filled with corpses left to rot, and ships were loaded with bodies and abandoned at sea. The plague circulated till around 590 A.D. Many villages and towns were depopulated. The Moors retook North Africa, the Goths retook Italy, the Persians sacked Antioch, and the Huns nearly took Byzantium itself. The population losses from Justinian’s plague took some 200 years to recover. During this period, the Islamic Empire established itself. The Byzantines and Arabs first clashed in the late 620s, while the Prophet Mohammed was still alive. After Mohammed’s death in 632, fighting continued until 718, by which time the Islamic Empire had stripped Byzantium of the Middle East, North Africa, and Cyprus. The Byzantines believed this was divine retribution for the sins of the Christians. Doubtless the Moslems agreed!