The Historical Significance of Micro-parasitic Infection as Detailed in William McNeal’s Plagues and People

 

by: Giovanni JRC

 

William McNeal, author of the book called Plagues and People, devised a persuasive argument as he contended that the microscopic world of single and multi-celled organisms played, and still continue to play, a significant part in human history.  Because the study of microbes and their effects on humanity are often limited to biological and anthropological inquiries, this notion is a relatively new aspect in the investigation of historical events.  Nonetheless, historians did record numerous accounts of illnesses and diseases that swept entire nations such as the Black Death in Europe, the small pox in the New World, and others which rendered these civilizations subject to change.  In essence, McNeal furthered these mere accountings of historical events as he studied the consequences of these large-scale infections and how it influenced the eventual interactions between various cultures. 

            He achieved this by first outlining a pattern of interface between early humans and the microscopic world around them.  He stated that early in history, humans were subject to the limitations and boundaries the micro-parasites created.  Micro-parasites, which McNeal defined as, “tiny organisms—viruses, bacteria, or multi-celled creatures as the case may be—that find a source of food in human tissues suitable for their own vital processes,[1]” essentially “preyed” on their human hosts and since early humanity’s exposure to these organisms were limited, their susceptibility to infection and death was

very high.  Nonetheless, prolonged contact with microbes within their area of habitation caused the early humans’ physiologies to adjust to the organisms.  McNeal emphasized this by stating, “Prolonged contact between human host and infectious disease creates a pattern of mutual adaptation which allows both to survive.[2]”  Thus, a symbiotic relationship is achieved since the parasites can live within their hosts, and humans benefit from the immunity they gained against surrounding microorganisms.  However, because of the numerous types of thriving microorganisms, single and multi-celled, which spread throughout the world.  Early humans were only able to maintain immunity against parasites within their region of habitation.  Thus, venturing out of their immediate territory exposed them to new forms of possibly fatal diseases.[3]  An example of which was the “sleeping sickness” of the African savannah.  Non-fatal to their antelope hosts, the microorganism called trypanosome inhabited a small region of the savannah where tsetse flies abound.  Because these tsetse flies were the main modes of transmission of this disease, early humans kept their distance from these areas were previous experiences dictated that if they ventured forth, they would contract the “sleeping sickness” (since they did not know it was the flies that caused the deaths).  Incidentally, this also kept the human hunters from preying on the antelopes thus they are still abundant in the savannah to this day.[4]  This example demonstrates McNeal’s idea that micro-parasites limited the areas in which humans can live and where they can migrate to.  He, however, did not mention that although the climates in Africa and the Levant were quite mild, the rest of the world was still cover in ice due to the Pleistocene.  This may also have contributed to the inability of humans to migrate to these parts of the globe. 

            According to McNeal, another way these lethal microbes limited the spread of humans throughout various continents was by the way they regulated population growth.  Because multi-cellular organisms did not elicit an immune response from the body, and medical knowledge to combat such illnesses was nonexistent, humans had always been susceptible to such infections.  Thus, when populations increased, which were conducive to the spread of multi-celled parasitic infections, death from microbial diseases ensued.[5]  Through this process, the increase in human population was negated by these hazards.  Due to this, the early humans had no need to migrate and spread to other available land masses because their numbers were too few to begin with.  

            Despite the overwhelming effects of these organisms, humans were able to adapt as they devised social restrictions to evade these unknown assailants.  For example, because of the apparently mysterious sources of these sicknesses, early man associated these hazards with religion and spirituality.  Because of this, they created religious taboos to prevent such infections.  Examples of which are the Jewish and Moslem prohibitions regarding the consumption of pork.  McNeal stated, “This appears inexplicable until one realizes that hogs were scavengers in Near Eastern villages and quite capable of eating human feces and other ‘unclean’ material.  If eaten without the most thorough cooking, their flesh was easily capable of transferring a number of parasites to human beings.[6]”  Thus, because of man’s ability to adapt to any environment and use the resources available to him, population growth ensued.  With this came the need for a change in subsistence strategy from hunting and gathering to farming and animal domestication in order to sustain a larger number of people within the society.  This shift resulted in the production of surplus goods and the notion of wealth.  With this, came the need for more organized governments and the protection of boundaries which led to McNeal’s notion of Macro-parasitism.

            Mirroring the interaction between parasites and humans, the development of governments eventually resulted in a symbiotic relationship between rulers and subjects.  As the peasantry provided goods and services, the ruling class granted protection and religious affirmation.   Initially, the relationship was quite similar as to the first encounters between new microorganisms and humans.  McNeal stated, “the hard-pressed peasantries that supported priests and kings and their urban hangers-on received little to nothing in return for food they gave up.[7]”  Eventually, reciprocal relationships ensued which resulted in more stable forms of societies.  However, such stability had its drawbacks for along with it came a sudden increase in population in a relatively small area.  Because these conditions were greatly conducive to microbial infections, diseases and illnesses attacked these large civilizations.   Furthermore, since there were large numbers of human hosts, micro-parasites thrived.  One of the examples given by McNeal was the outbreak of the plague in Europe caused by organisms called Pasteurella Pestis.[8]  Brought by Genghis Khan’s men from the northern steppes, they inadvertently contracted the “plague carrying” fleas from endemic rats of Yunnan and Burma.  Since the local inhabitants of these lands established various protocols in dealing with the native rats in order to avoid contracting the disease, they were not harmed at all.  However, unfamiliar with the hazards, Genghis Khan’s men disregarded the local customs thus receiving infections.  Eventually, these soldiers spread throughout the Eurasian continent in a macro-parasitic fashion inadvertently carrying micro-parasites.  Thus, by 1346, an outbreak ensued killing a large population of Europeans and Asians throughout the continent.[9]  The spread was mapped in McNeal’s book (see figure 1).[10] Other diseases also visited heavily populated civilizations like Europe and China such as the influenza, polio, cholera, leprosy, mumps, measles, small pox, and others either passed from “animal carriers to humans” or “human-to-human” contact.  Because of the body’s ability to adapt to most of these diseases, some of these illnesses eventually became non-hazardous as the hosts’ bodies “learned” to symbiotically co-exist with their parasites.  Furthermore, practices such as quarantines for the sick, covered sewer systems, better building materials, and early experiments in inoculations aided in the limiting of more outbreaks.[11]  Also a more organized medical field was developed.  McNeal stated, “Organized medicine thereby began for the first time to contribute to population growth in a statistically significant fashion.[12]”  However, although McNeal mentioned that these practices already existed in other cultures, he essentially called them “quackeries” when they proved to be effective and was later on implemented by the Europeans.  In fact, although McNeal called them “folk practices,[13]” medical knowledge was much more advanced in the East.  Furthermore, European universities eventually adopted these Eastern medical treatises as the standard texts for their medical teachings.

 After recovering from these various conditions and gaining immunity, the populations of European countries once again increased while relegating some of these once debilitating ailments to mere “childhood diseases.[14]”  As a result of this new found “health,” the sharp rise in population led to another macro-parasitic act, the need for expansion and subjugation through armed conflict.

            Unknowingly, European expansionists brought, within their bodies, potentially lethal parasites the rest of the world had yet to encounter.  Because of their developed immune systems, they were not affected by the micro-parasites they carried.  However, inhabitants of isolated areas like the American continent proved to be highly susceptible to these afflictions.  McNeal stated, “No wonder, then, that once contact was established, Amerindian populations of Mexico and Peru became the victims, on a mass scale, of the common childhood diseases of Europe and Africa.[15]”  Although civilizations such as the Aztecs and Incas had the population density to cultivate diseases indefinitely, they did not seem to.  McNeal surmised that because their domesticated animals such as the llama and alpacas never made contact with any possible microorganisms that carried diseases for they were too few and too dispersed.[16]  Thus, when the highly immune Europeans brought their lethal parasites, the formerly isolated Amerindian populations were infected almost immediately.  As a result, they were subjugated quite easily to the point of converting to the conquistadors’ religion of Christianity.  McNeal credited this easy subjugation to numerous reasons.  First, their customary ways of preparing food and their diet of maize that led to vitamin deficiencies.[17]  Another reason was that there was already an ecological strain in the empires due to population growth.  McNeal added, “All these factors therefore conspired to make Amerindian populations radically vulnerable to the disease organisms Spaniards, and before long, Africans brought with them across the ocean[18]”

 

 

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