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20201213 – Plagues and People



Author defined very nicely and briefly the main idea this way:” This book aims to bring the history of infectious disease into the realm of historical explanation by showing how varying patterns of disease circulation have affected human affairs in ancient as well as in modern times.”


Here author describes what prompted him to write this book: the story of conquest of America when a few hundred conquistadors overcame millions of indigenous people organized in Aztec empire. Author rejects the usual explanations such as firearms, horses, mistaken identification of white Spaniards as gods, and such. He sees the key to this conquest in biological weapons unwittingly unleashed on population without immunity that not only killed millions, but also undermined morals by convincing people that gods on the side of conquistadors because they do not get inflicted by disease.  

Author also defines a few key concepts such as microparasites such as bacteria and viruses that gets people sick or even kills them and macroparasites such as big predatory animals, but also great warriors and aristocrats, foreign and domestic, that rob, enslave, and kill people.  Author is looking at interaction between victims and parasites as complex process with wide range of system equilibria in the range from deadly parasite, either micro and macro, which kills, consumes, and then have to find the next victim or die, all the way to coexistence parasite, which just consume some share of victim’s resources, allowing it staying alive and even being well. Author then discusses some specific microparasites and how they interact with human body.

I: Man, the Hunter
In this chapter author looks at the humans as hunters with powerful information processing tool – brain that allow practically eliminate all other large predators that could compete with humans for food and other resources. Author reviews parallel evolutionary development of humans and their parasites and how superior communication and organization skills allowed humans establish dominance over predators. Then something unusually author uses different reference point: “Looked at from the point of view of other organisms, humankind therefore resembles an acute epidemic disease, whose occasional lapses into less virulent forms of behavior have never yet sufficed to permit any really stable, chronic relationship to establish itself.” Author also makes here a very important point that coevolution of humans and their microparasites in Africa led to establishment of equilibria when human grow was limited by diseases well adjusted to humans. Author also notes that limited amount of naturally produced resources also limited human macroparasites. Finally, author discusses breakthrough that occurred between 40,000 and 10,000 BC when humans moved out of Africa, in process leaving behind their natural microparasites as limitation of their growth, and expanded all over the earth eliminating other humanoids and big predators. Once again worldwide equilibrium was established with human numbers limited by availability of resources with humans divided into huge diversity of types well-adjusted to the huge diversity of environments.

II: Breakthrough to History
Author begins this chapter with discussion of practical elimination of large-body animals that occurred everywhere where humans expanded their habitat. Only domesticated big-body animals expanded their presence. The overall impact was shortening of food chains and decrease in diversity of environment. Then came agriculture, which took out huge amount of space away from natural development into artificially limited diversity of plants and animals. Author discusses in some details agricultural processes and how their impacted various parasites, both micro and macro. Author also looks at cultural patterns that sometimes limit, but sometimes expand vulnerability, such as communal baths. Here is how author presents established equilibrium:” Eventually agricultural populations became dense enough to sustain bacterial and viral infections indefinitely, even without benefit of an intermediate nonhuman host. This cannot ordinarily happen in small communities, since unlike multicelled parasites, bacterial and viral invasions provoke immunity reactions within the human body. Immunity reactions impose drastic alternatives upon the host-parasite relationship. Whenever they dominate the interaction of host and parasite, either speedy death of the infected person or full recovery and banishment of the invading organism from the host’s body tissues ensues—at least for a period of time of months or years until the immunizing antibodies fade from the bloodstream so as to permit reinfection.”

Author then reviews transmission of infection either direct or via animals and provides this nice table for number of diseases shared with animals:

Finally, author discusses interactions within civilization, its balance between cities and rural areas that supplied constant flow of new people to compensate for losses from proximity of people – necessary condition for both high economic opportunity and high infection diseases vulnerability.

III: Confluence of the Civilized Disease Pools of Eurasia: 500 B.C. to A.D. 1200
In this chapter begins with estimate that by 500 BC macroparasitic balances were established in several civilized areas. Similarly microparasitic balances specific to agriculture were established in older cites, but author notes that:” By contrast, greater instability prevailed in fringe areas where three different natural environments—the Yellow River flood plain, the monsoon lands of the Ganges Valley, and the Mediterranean coastlands—had all become capable of supporting civilized social structures much more recently than was the case in the Middle East. Accordingly, in 500 B.C. ecological balances were still precarious in these regions, and there is reason to suppose that disease patterns were far less firmly fixed than in the Middle East.”  Author methodically goes through such areas estimating microparasitic conditions around 500 B.C. After that for some 1700 years these civilized centers where preparing surrounding populations for expansion by developing their immunity via intermittent interactions. Here is how author describes this process:” The conquests and ethnic encroachments which Turks and Mongols achieved before, and more spectacularly after, A.D. 1000 simply could not have occurred had these peoples not achieved and maintained a level of immunity to civilized diseases almost equivalent to that prevailing in the major civilized centers themselves. Everything known of the trade patterns and political structures of the steppe make this seem likely, indeed all but certain. Frequent movement across long distances, and occasional assembly into large gatherings for raids or (with the Mongols) for a great annual hunt, provided ample opportunity for infectious diseases to be exchanged and propagated among the nomads, and even, as Chinese records attest, to be sometimes communicated to less mobile civilized populations.”

IV: The Impact of the Mongol Empire on Shifting Disease Balances, 1200—1500
Here is how author describes situation before development of Mongol empire: “Two systematic instabilities remained. One was the persistent and cumulatively massive growth of human population in the Far East and Far West, resulting from the way in which the Chinese and Europeans had broken through older epidemiological and technological barriers shortly before A.D. 900. Eventually this development affected the macro-balances of the Old World in emphatic fashion, making first China and then western Europe critically influential in military, economic, and cultural matters. The other source of systematic instability within the Eurasian world balance, as defined between 900 and 1200, was the possibility of further altering communications patterns, both by sea and land.”

Expansion of Mongol led to increase of communication and their shift up North. “From an epidemiological point of view, this northward extension of the caravan trade net had one very significant consequence. Wild rodents of the steppelands came into touch with carriers of new diseases, among them, in all probability, bubonic plague. In later centuries, some of these rodents became chronically infected with Pasteurella pestis. Their burrows provided a microclimate suited to the survival of the plague bacillus winter and summer, despite the severities of the Siberian and Manchurian winters. As a result, the animals and insects inhabiting such burrows came to constitute a complex community among which the plague infection could and did survive indefinitely.” Then author discusses the history of raise and fall of the most important disease that emerged from this situation – plague. After the plague other epidemic diseases became prevalent and author connects it to development of textile industries that provided warm closing in cooling European climate, creating simultaneously good conditions for lice. The final evaluation of this period goes like this:” What we see, then, as the over-all response to the changed communications pattern created in the thirteenth century by the Mongols is a recapitulation of what we saw happening in the first Christian centuries. That is to say, massive epidemics and attendant military and political upheavals in Europe and (less clearly) also in China led both in the early Christian centuries and in the fourteenth century to sharp diminution of population in the Far East and in the Far West; but in the regions between, both epidemic history and population history are difficult or impossible to discern. In the earlier instance, several diseases were probably at work, and it took a longer time for population to recover, especially in Europe. In the fourteenth century, on the contrary, a single infection was probably responsible for most of Europe’s population decay, and recovery both in Europe and in China was swifter, so that by the second half of the fifteenth century unmistakable population growth again set in at each extreme of the Old World ecumene. Even in Muscovy and the Ottoman empire, lands lying close by the steppe focus of plague infection, population growth became unmistakable in the sixteenth century, perhaps beginning even earlier.”

V: Transoceanic Exchanges, 1500—1700
This chapter is about globalization of humanity during period 1500-1700 when Euro-Asian civilization clashed wit independently developing Amerindian civilizations and crashed it do significant extent via epidemic defenselessness of the latter. It was not one sided, but European diseases were much more virulent than American. The result was forfeiture by Amerindians of their culture and believes because their gods failed, leaving them without ideological power to resist. Author, however describes not only European epidemiological conquest, but also European defeats by local microparasites in such places and Africa and Amazonia. Author also describes exchanges of plants and animals, which to significant extent changed both environment and peoples, eventually resulting in decrease of diversity. Author also discusses a parallel process when macroparasitic development led to dominance of countries with superior military equipment and tactics. Author concludes the chapter by stating that these:” … factors continue to affect the conditions of human life in the twentieth century. Indeed, the world’s biosphere may be described as still reverberating to the series of shocks inaugurated by the new permeability of ocean barriers that resulted from the manifold movement of ships across the high seas after 1492. Yet almost as soon as the initial and most drastic readjustments of the new pattern of transoceanic movements had subsided, other factors—scientific and technological for the most part—inaugurated still further and almost equally drastic changes in the world’s biological and human balance.”

VI: The Ecological Impact of Medical Science and Organization Since 1700

In the final chapter author reviews how medical development such as inoculation and then vaccination changed human interaction with microparasitic environment providing new patterns of human development all over the world. Here is how author concludes this book:” In view of the truly extraordinary record of the past few centuries, no one can say for sure that new and unexpected breakthroughs will not occur, expanding the range of the possible beyond anything easily conceived of now. Birth control may in time catch up with death control. Something like a stable balance between human numbers and resources may then begin to define itself. But for the present and short-range future, it remains obvious that humanity is in course of one of the most massive and extraordinary ecological upheavals the planet has ever known. Not stability but a sequence of sharp alterations and abrupt oscillations in existing balances between microparasitism and macroparasitism can therefore be expected in the near future as in the recent past. In any effort to understand what lies ahead, as much as what lies behind, the role of infectious disease cannot properly be left out of consideration. Ingenuity, knowledge, and organization alter but cannot cancel humanity’s vulnerability to invasion by parasitic forms of life. Infectious disease which antedated the emergence of humankind will last as long as humanity itself, and will surely remain, as it has been hitherto, one of the fundamental parameters and determinants of human history.”


I really like author’s approach of looking in parallel at micro and macro parasitic phenomenon.  Usually it is separated into two different areas: epidemiological and military / state histories, but in reality it makes a lot of sense looking at them together because it is pretty obvious that epidemic deceases worked hand in hand with military endeavors sometime bringing unrealistically huge benefits to attackers as was the case with conquistadors, but sometimes protecting locals against superior military power, as was the case with Napoleon’s troops on Haiti. Granted, bioweapons were used unconsciously, but they were highly effective anyway. This brings me to recognition that what we usually consider as conscious actions leading to some expected result in reality is much more dependent on poorly understood environmental circumstances, which makes great leaders and conquerors only slightly more effectual driving force of change than some completely unconscious bacteria.    

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