What a cheerful title for the first essay of the month!
I’m starting with the simple topic of disease — not its causes; not its treatment; its existence — because its influence on human history is quite simply incalculable. We may grumble about getting colds during the winter, but Pestilence is one of the Four Horseman of the Apocalypse, right up there with War and Famine, the harbingers of Death itself. Our ancestors feared disease to a degree we can scarcely imagine today, with our antiseptics and antibiotics and vaccines, our understanding of where disease comes from.
First things first: the term “disease” can mean a lot of things, ranging from infection via pathogens to problems caused by nutritional deficiencies to congenital or degenerative conditions. For the most part I’m going to be focusing on the first two categories.
These problems have been with us from the start . . . but if you go back far enough, they actually weren’t as bad as they became later. Mobile hunter-gatherer societies didn’t live in close proximity to livestock, giving a wide range of zoonoses ample opportunity to adapt to human targets, and they didn’t maintain large enough communities for any epidemic to really gain momentum. They also tended to have more varied and balanced diets than early agriculturalists, meaning they were less vulnerable to deficiencies.
Once we settled down and started living with pigs, though, the scene changed quite radically. Diseases and malnutrition became rampant . . . and the greatest fatalities were among small children. In some places and times, infant mortality rose as high as fifty percent: one in two kids dead before the age of five. When you see statistics about how the life expectancy in such-and-such place and time was only thirty-two, that number often includes infant mortality in the overall calculation. People who survived childhood had better prospects.
Sadly, although colostrum helps to protect infants against certain scourges, people often believed it was unhealthy, and deliberately discarded it. And of course the mother might or might not survive long enough to provide anything to her baby, depending on whether she bled out in delivery, or was caught too strongly in the grip of puerperal fever thanks to the filthy hands of the midwife or physician — but that’s a topic for a future day.
The litany of infectious diseases is well-nigh endless. Smallpox, measles, mumps, rubella, whooping cough, typhoid, malaria, yellow fever, dengue, cholera, dysentery, polio — I could keep going. And of course any wound risked getting infected; the question was whether the infection would be a small one you could fight off, or a bad one that would turn to gangrene and kill you. Even those who survived often paid a price, whether in the form of scars (Queen Elizabeth I wore such thick makeup in part to hide her smallpox scars) or long-term disabilities like muscle atrophy, hearing loss, blindness, or brain damage.
And then there are the problems caused by nutritional deficits. Rickets, for example, is caused by vitamin D deficiency — it’s the reason why the milk in the grocery store is often fortified with vitamin D, and one of the reasons people drank cod liver oil — and it softens bones so that the legs often become bowed, along with overall growth being stunted. Beriberi or thiamine deficiency is linked with a diet heavy in white rice, because polishing away the bran removes most of the vitamin B1. And of course scurvy is probably the most well-known deficiency — and we actually figured out how to fix that one long before we knew why the solution worked. (Which then backfired a couple of centuries later. Due to complex circumstances, the lime juice polar explorers carried with them had more or less denatured its vitamin C, which meant they got scurvy and everybody went “holy crap, apparently this isn’t the solution” and fell down a rabbit hole of thinking it was a bacterial problem.)
I’ve been talking about deficiencies, but it’s also possible to end up sick because you had too much of something — and I’m not just referring to obvious poisons. There’s a good reason gout stereotypically shows up as a disease of the rich; high consumption of meat and alcohol leads to high levels of uric acid, which then forms crystals and causes pain in the joints. But historically, your average commoner has had more to fear from not enough of a certain nutrient rather than too much.
Other conditions seemed so inexplicable in rational terms that they were considered to belong to the realm of magic, not the physical body. Progeria, which looks a bit like extremely premature aging, may be one of the elements that gave rise to stories of changelings. Seizures from epilepsy may be interpreted as possession or the action of a curse. And even now, people in many parts of the world view albinism in a superstitious light, and often a profoundly negative one: in Tanzania and Burundi, albino people have been killed so their body parts can be sold for magic potions.
Genetic conditions rapidly move into a realm too technical for me to discuss them in detail, but I do want to draw out one thing, which is the tradeoffs our biology sometimes makes. Sickle cell disease is vastly more common in sub-Saharan Africa, and to a lesser extent in other tropical regions, than it is in temperate areas; that’s because it’s the unfortunate side effect of malarial resistance. One copy of a certain gene gives you protection, but two gives you sickle cell disease. There’s also a theory that HIV resistance in certain populations is a result of the Black Death: the mutation that causes it may have helped their ancestors survive that pandemic.
But that kind of thing is invisible to people without modern science. Which is true of a great many things about disease, from their causes to their progression to how best to cure them. And nowhere does this become a more urgent concern than in times of plague . . . which will be next week’s topic.