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  • Disease and Cold Drive History

    Posted by Assistant Village Idiot on February 29th, 2020 (All posts by )

    Update: For example, drought.

    This was not prompted by Coronavirus discussions in any way. My reading and podcast listening the past month have both led to considerations of disease affecting historical events. I have several times thought it would be fun to talk with Trent and Mike K about the subject over a beer or three.

    The effect of disease on historical events has usually only been mentioned in extreme cases, when it is obvious that at least some influence must have occurred.  The effect of smallpox on the Aztecs, or the Black Death on the economics of Europe receive some mention, but even in those cases summary histories can leave them out. Amazing, but true. There has been some increase over the last twenty years of historians addressing the issue of disease directly, and the last five years has seen an explosive growth in that approach because of what we can learn from archaeology rather than written records.  What has then happened is that the text historians have doubled back and acknowledged “yes, this was there all along, but because we could not clearly understand symptoms nor measure extent we could not make definitive statements.” So they mostly said nothing.

    Or, as I suspect, they preferred other explanations, as we all have, due to the training in how to look at history we have all grown up with. I may be partly guilty myself.  I have heard doctors offer up possible medical explanations they have run across in their reading, only to be greeted with blank looks and polite smiles.  No, silly.  It’s kings and battles and trade routes and technological advances. Diseases are just there all the time and have only a marginal effect. I have been only slightly more sympathetic until the last decade,

    I recall reading in the 1970’s an article on the colonisation of New England which claimed the Puritans were remarkably fortunate in when they arrived, as the Indian population was only about a third of what it had been in 1607.  The idea was that they had wiped each other out in a series of battles. Otherwise, the Englishmen would not have had a chance. We now know that those natives were first depleted by the diseases they had picked up in trade contact with Europeans in what are now Maine and Nova Scotia.  The battles came as a result of that, as tribes tried to move into territory devastated by disease. They died of European diseases, then wiped each other out before 1620. That remaining third was further depleted by additional diseases after year-round settlers came.  In temperate climates the losses were fewer.  In New England, it may have been “only” 80% of the natives who died from disease.  In Mesoamerica, with denser settlement, it may have been 95%. In the absence of any understanding of germ theory, this was doubly devastating psychologically.  Your leaders, your shamans, your customs had all failed. There was nothing to cling to.  You concluded that the invaders were favored by the gods. Who wouldn’t?

    India and China, both of which have both temperate and tropical zones, have centuries of the same pattern repeating.  An invader arrives from the Northwest.  They are from temperate zones, tall, strong, and healthy.  They easily defeat the inhabitants and take over lands ever southward. Then they catch tropical diseases, they die, and they retreat back northward.  Sometimes they go all the way back to lands they came from.  Other times they go back only halfway, and settle.  They gradually acquire a little immunity to the tropical diseases, but the two groups essentially settle into a north-south division of very different groups.  The Dravidian languages are not at all closely related to the Indo-Aryan languages. Take whatever political explanation you like about weaponry, organisation, and culture. The climate line, and thus the disease line, explains a thousand years of history more exactly. See also Mongols, China. (The Mongols later also destabilised the entire Eurasian continent, by disease as much as horsemanship.)

    The new invaders also bring new diseases, which can devastate the tropical population. Yet in the end, holding the territory becomes impossible for those from temperate climates. Only those who have a culture of raiding rather than settled conquest can survive on the edge of those lands: Saxons, Picts, Huns, Mongols, Sueves, Yamnaya, Apaches, Comanches, Bedouins, Vikings, Berbers.* Europeans could extract wealth from the coasts of Africa, but even now have trouble living in the interior. Malaria and other diseases take their toll. If a section of jungle is cleared for cultivation, the mosquitoes take over, and the death rates soar.  In a stable period, the humans and the microparasites establish a balance over time, neither conquering, neither eliminated.

    The temperate zones have their own diseases as well, often those which can adapt by going dormant for months in dry or cold seasons. The macroparasites, the other humans, upend the balance, with unpredictable results.

    The inhabitants of cities have a similar “advantage” over the outside invaders. They may be sickly and less strong, but diseases have already wiped out many of their siblings in childhood. They have the immunity of those who have been exposed to many more diseases. The invaders arrive again and again, tall and strong, but cannot hold the cities they take. The Goths and Vandals wrought havoc, conquered and settled in the Roman Empire, and ruled sections of it for a short time. Then they were inexplicably defeated by the armies of the empire a few decades later. Their star burned bright and flamed out. Historians have offered many possible explanations about military mistakes, trade routes, feckless emperors. All of those things have some truth. Disease is not 100% determinative. But the new thinking is that if you have to pick one factor to oversimplify with, go with disease, and second, natural disaster.

    Justinian, emperor of the eastern empire, was determined to retake and restore the west in the 6th C. He succeeded. He put the Goths and Vandals on the run. Unfortunately, the weather was already turning colder than the warm centuries that marked the height of Roman power when at least two major volcanic eruptions elsewhere turned the entire world cold in the late 530’s. Those produced the coldest years in the last 2000. Harvest were bad, and then nonexistent. Onto this was added the Bubonic plague – what was long speculated has recently been confirmed by DNA – which wiped out at least half, and perhaps as much as 75% of the population of the western Mediterranean. The cities collapsed, the various armies of Goths and eastern empire raided the countryside for whatever food they could find. Rome’s population fell from 350,000 to 50,000 in a century or less.

    When disease and starvation take your population out, they take the old and the young.  In 546 AD in the western ex-empire, there were no young children, no old people in the villages. This was less true as one headed north, but still essentially true all the way up to Scotland and Scandinavia.  There had been people, and cities, and trade, now there was not even food. Cultures with a tradition of raiding survived.  Those with traditions of armies and governments did not.  In the Eastern Empire this was nearly true as well, as that half almost fell a few times in those centuries.

    Dense populations create more diseases, and sometimes a new variant can be devastating.

    I don’t think it would be efficient to try and link you to various episodes of a couple of the podcasts I am listening to nor the authors they recommend, but the original text is William MacNeill’s Plagues and Peoples from 1976.  It was updated in 1998 in an effort to explain AIDS to the general reader. His explanations were sniffed at in the 70’s, drew grudging respect by the 90’s, and are now considered to be the foundation of the art of seeing history through the prism of disease.

    Historians who credit climate for dramatic upheavals seldom mention that it is cold that is the problem, not warming.

    *The idea that the Huns or Mongols could have conquered Europe except for good luck for my ancestors because the Asian warriors had to double back because of battles of succession back East is almost certainly false.  They conquered all before them, but they were steppe peoples who depended heavily on grasslands for their horses.  The steppe ends in Hungary, and they could only raid beyond that. They were not turned back by Pope or battle.  They raided as far as was profitable and went home. There is also evidence in both cases that their ranks were slowly depleting to new diseases.  They may have brought worse than they got, but their supply lines were longer.


    8 Responses to “Disease and Cold Drive History”

    1. Mike K Says:

      Nice discussion. Back in the 1930s, a biologist named Hans Zinsser wrote a book called, “rats, Lice and History” that began much of this field of considering diseases and history.

      More recently, Greg Cochran co authored, “The 10,000 year explosion,” which is more about genetics and evolution but which also discussed the role of European diseases on the Amerindians who had been isolated for 10,000 years. The result was an immunological desert, which left them vulnerable to disease but also vulnerable to alcoholism and largely free of autoimmune diseases like rheumatoid arthritis.

      The IndoEuropeans conquered northern India and left the case system as evidence. Africa has remained a death zone for Europeans, while north and south America were settled by the Europeans.

    2. Assistant Village Idiot Says:

      I am a big Cochran fan, as you may remember.

    3. Gavin Longmuir Says:

      Disease and the planet’s ever-changing climate certainly have had impacts on the path of human development. It is good to recognize those factors, such as how life improved for many during the Roman Warm Period and the Medieval Warm Period, but they are surely not the only factors driving history.

      Some historical situations can clearly be tied to diseases, and to different natural resistance to specific diseases among particular populations. Africa was the “Dark Continent” because most Europeans succumbed to diseases there, and consequently little was known about the continent beyond the coastline. The Scottish attempt to colonize Darien in Central America failed in large part because of diseases. The original French effort to build a Panama canal collapsed in the face of mosquito-borne disease.

      On the other side, many events in history do not seem to be related to diseases. Disease apparently played no part in the Roman extirpation of the Carthiginians — history would have been very different if that conflict had gone the other way. The post-Mohammed expansion of the Arabs all the way to Spain apparently did not involve a disease component. The historically-significant decision of a Chinese Emperor in the 1400s to close the borders and stop technological progress for 500 years was not driven by disease.

      Arguably, sanitation has been more important than disease — although that could be regarded as a fine distinction. In one of Prof. Harl’s excellent Great Courses series, he mentioned that a couple in Roman times needed to have about 10 children just to maintain the population. The island of Bahrain in the Middle East has extensive well-preserved pre-Islamic burial grounds — and about half the bodies were children. In more recent times, improved sanitation reduced the death rate among the young and allowed the population to grow. Thus, in the 19th Century, France exported part of its expanding population to Algeria. As French standards of sanitation cut the death rate among Algerian children, by the later 20th Century Algerians were moving into France.

      Many factors have had impacts on populations and history. Let’s give them all proper consideration.

    4. David L. Says:

      On a more micro level, I recall an article a few years ago detailing that one of the major reasons for the weakness of Cornwallis’ army at Yorktown was a high incidence of malaria after spending an extended amount of time in the Carolinas.

      Washington’s army, having arrived much more recently from further north, had not yet had time to suffer serious effects from malaria, and was thus much stronger.

    5. Lewis Levi Pearson Says:

      I think that Mr. Says is correct about Cornwallis’ troops being more debilitated by disease than George Washington’s. He is incorrect in suggesting that malaria was not found in New York, New Jersey, and Connecticut during the revolution. It was endemic in those places until just prior to WWI. It may have been less of a problem because of the winter protection from mosquitoes, and the years of the revolution included very cold periods.

      The role of smallpox in the revolution was probably more important. The Europeans had relatively high immunity. The Americans who fought for America were inoculated by Washington. The British did not do so for their Americans; and particularly the African American loyalist troops were absolutely devastated by smallpox. The Indians were similarly affected.

    6. Cornfed Says:

      That disease has enormous population effects is well understood by biologists, epidemiologists etc. and it makes perfect sense in hindsight to read history in this light, but the author is spot on in recognizing how we simply have not, until recently, looked at history this way. I love reading historical books, particularly explorers, conquerers, shipwrecks, and so forth. You dont’ have to read very many to be struck by the disastrous effects of diseases. Exploration parties and colonizers were routinely decimated by them, particularly in the tropics.

      This is a bit of a tangent, but I am a botanist and as I read this article, it reminded me of an instance in college. One of my professors was wondering why a particular plant thrived in its dry, native habitat, but languished when planted in the garden under presumably more optimal conditions. The answer was a fungal disease that thrived in warm moist conditions, but could not live in dry conditions. When a funcigide was applied and the disease cured, the plant exploded with growth. The parallels with human civilization do not need elaboration.

      Not only do people suffer from diseases new to them, they also suffer from pathogens and parasites endemic to them. Tribal populations are often found to harbor high levels of parasites that take their toll. Nobody, not even the natives themselves, realized that the parasites were putting a very tight lid on their vigor (for lack of a better phrasing). Often, the perception that a population is immune to endemic disease is a mistake, and “tolerant” would be a better word. So diseases have an (unknowable) effect in this way too.

    7. yara Says:


      from Mankiw’s ten principles of economics: “Rational people think at the margins”

    8. Mike K Says:

      The role of smallpox in the revolution was probably more important.

      Napoleon had his army vaccinated and gave a testimonial to Jenner after releasing a prisoner at Jenner’s request. By 1870, the French army had forgotten Napoleon’s advice and was devastated by smallpox during the Franco-Prussian War, while the Prussians used vaccination to protect their army.

      Malaria was endemic in much of the US even as late as post Civil War. Doctor Mayo moved his family to Minnesota from Missouri to avoid malaria. The mosquito was not identified as the vector until after 1900 but Civil War hospitals had mosquito nets over beds.