Diseases Didn’t Just Shape History, They Control the Future

The success of the conquistadors has been attributed to guns, germs, and steel, but you could also point to a quirk of fate: The New World has fewer domesticable animals than the Old and fewer that live in large herds like cows and sheep. As a result, infectious diseases have had less chance to incubate and jump the species barrier to humans, and so people living in the Americas had never had the chance to build up immunity to pathogens like smallpox, which is thought to have jumped from livestock to humans in the early days of agriculture, around 10,000 BC. 

There are other compelling examples of germs changing the course of history: how the Black Death reduced the working population and made labor more valuable, sparking the end of feudalism; how malaria rendered much of Africa impenetrable until the 1880s until the widespread use of quinine (which comes from the bark of the South American cinchona tree).

Diseases may also be responsible for the spread of religions like Christianity, which exploded in popularity after the third-century Plague of Cyprian, which was, some scientists now believe, a type of hemorrhagic fever similar to Ebola. Christianity encouraged acts of kindness as a route into heaven—rather than fleeing from the sick, Christians nursed them back to health, drastically improving their survival rates. “Even with basic nursing, providing people with water and food, you could maybe save two-thirds of people who were sick,” Kennedy says. To the untrained eye, this would have looked a lot like a miracle—the best kind of publicity for any new religion. In comparison, “paganism didn’t provide a very helpful way for interpreting the impact of infectious disease outbreaks,” Kennedy says.

But the spread of Christianity also spread the notion of man’s dominion over nature. In the long term, that attitude has contributed to climate change and driven our relentless push into remote areas, both things that can distribute new diseases as we rub up against nature in strange new ways. 

Things came full circle with Covid, though. It remains to be seen what impact the latest pandemic will have. “Being in the eye of the storm it’s hard to tell, but if we look back at history there’s so many cases of pandemics, epidemics coming along, killing lots of people, harming societies, and creating the space for new ideas and new societies to emerge,” Kennedy says. “Probably when we look back at this period we’ll see that there were changes that were maybe already underway, but that Covid-19 has either accelerated them or changed the trajectory of history.”

Covid has perhaps already served as a humbling reminder of the natural order of things. “It’s been quite a shock to the way in which a lot of us see the power of humans,” Kennedy says. “You can make a pretty good argument that we have been living, and still live, and always will live in the age of microbes. Coming to terms with that is part of really learning how to live successfully on this planet.”

(Pathogenesis: How Germs Made History by Jonathan Kennedy is published on April 13.)