William McNeill’s “Plagues and Peoples” seems like an interesting enough book, but for some reason I haven’t spent much more time reading it since the last post on it. Still, there are some things I should have mentioned then and forgot to, and a few additional notes from later on.

I came to this book on disease with a mind primed by Ewald & Cochran. Paul Ewald in particular in his book “Plague Time” rails against a theory that disease inevitably adapts itself to host populations, approaching symbiosis in the limit. Instead he points out that disease only needs you to survive long enough to make it to the next host, and otherwise views you as a resource-laden factory to be used up and thrown away. McNeil is one of those people who assumes the old theory. To him virulence is evidence that a disease is new. Particularly dangerous diseases are those with multiple hosts, and he thinks that’s because the disease had spent all that evolutionary time adapting to an older host and only recently made the leap over. “New Germ Theory” would argue instead that hosts like mosquitoes make diseases less reliant on healthy humans, thus reducing the cost of virulence.

McNeill does present some examples for his argument. One concerns a disease that was found among Brazilian rabbits called myxomatosis, which had a stable pattern of mild symptoms. It was deliberately introduced to the Australian rabbit infestation (which belongs to a different genus than New World rabbits) and had an initial fatality rate of 99.8 percent. Rabbit generation time being what it is, it didn’t take that long (in human terms) for the progressively milder symptoms to reach a steady state with a smaller rabbit population. In Canadian Indians, tuberculosis initially affected parts of the body unaffected among European settlers. After three generations it morphed to the familiar pattern of remaining in the lungs.

An entirely different point McNeill makes is that having fields like fallow has nothing to do with “replenishing soil”. Since I read the textbooks he derides when I was in school, that was news to me. He allows exceptions for “dry farming” where it is desirable that moisture be retained in the field, but otherwise regards any chemical changes as insignificant. Instead, “the great advantage of fallowing is that it allows farmers to keep weeds at bay by interrupting their natural life cycle with the plow”. I still don’t entirely get the logic behind that and the three-field system, but I’m not a farmer.

McNeill is at his most Jared Diamond-ish (really, I should say, Diamond is at his most William McNeill-ish) when he argues that civilization did not expand due to its attractions, but its disease advantage. He does allow though that sometimes uncivilized people had dangerous enough infections to stand their ground against the urbanites/farmers. He offers India as “a sort of test case”, where a civilization established cities in the relatively dry northwest, and after recovering from the Aryan invasion expanded to the point where it came into contact with “forest people” of the more tropical south. Here an “epidemiological standoff” ensued in which each side was vulnerable to the other. So instead of being virtually obliterated (like inhabitants of the New World) they were gradually incorporated as new castes, maintaining many old rites up to the modern era. McNeill displays a Marvin Harris-like functionalist attitude toward cultures, and so he interprets Hindu caste taboos as defenses against infection by vulnerable communities. This functionalism falls on its face occasionally, such as when he acknowledges rituals of ablution can actually encourage infection and that some mosques were found to have pools of water full of snails infected with schistosomiasis.

UPDATE: Reading further, McNeill claims that cities would have reached stability to the “childhood disease” point and so historical epidemics would have been characteristic of outlying regions. I could not refrain from rolling my eyes and laughing at him. Not that I know if there were more epidemics in those regions (of which we have fewer records) or cities, but he is downplaying an urban disease problem that is pervasive throughout urban history and my priors are heavily weighted on the opposite side of the scale.

UPDATE 2: A few more surprising claims. I had been taught that one of the few diseases to flow back from America to Europe was syphilis. McNeill acknowledges that there are no recorded cases of syphilis in pre-Columbian Europe, but thinks the disease just happened to evolve around that time. There was a leprosy-like disease called yaws which apparently spread through a spirochete identical to syphilis, but was both milder and widespread (rather than just among adults). Yaws declined in the later medieval years, and McNeill thinks that the increased use of clothing and decreasing use of huddling to survive the cold (except in Scandinavia) forced yaws to evolve into syphilis. Aside from leprosy, cold northern areas seem less afflicted by disease, and McNeill attributes the greater mysticism and ritual of Catholicism (in comparison to Protestantism) as a response to the greater inexplicable outbreak of epidemics in more southern areas. He also says that based on some sayings of Muhammad, Muslims took a much more passive approach to disease. This was surprising to me, since I’d heard that the Ottomans were using inoculation before Louis Pasteur was around. He argues that the disease toll on Muslim conquerors is what enabled the Christian populace of the Balkans to regain independence.