The American Plague: Why Wasn’t It a Thing?

Maritime expansion was one of the major turning points in the history of the world. Starting from when Christopher Columbus discovered the American continents in 1492, Europeans quickly saw profit, evangelization, and a new home in the Americas. However, this exploration was not without its consequences — notably, the rampant diseases that devastated the population of the Americas. From the 16th century to the start of the Victorian Era, the indigenous population of the New World dropped by a least 90%.

The conquistadores and company couldn’t possibly have killed that many people. Sure, they certainly killed a lot of the indigenous population, but their death count is nothing compared to what they brought with them: Smallpox, cholera, the bubonic plague, tuberculosis, typhus, influenza, mumps, measles, and more leapt from those first explorers to the coast, and made their way inland. The microscopic invaders spread quickly, eventually taking over virtually an entire hemisphere of people that had no defense against them. Tens of millions died. These germs decided the fate of the conquistadores’ battles long before the fighting actually started.

Now ask yourself: Why didn’t the Europeans get sick? If New Worlders got sick from Old World germs, then surely Old Worlders should get sick from New World germs.

Yet, there was no American Plague that ran rampant through Europe after the explorers came back. Europeans did not become infected with any New World diseases. Had such an American Plague existed, maritime expansion would have been drastically different; the world would be vastly different from what we know today.

Plagues

To answer why an American Plague wasn’t a thing, we first have to distinguish regular diseases — like the common cold — from plagues. Plagues have two defining characteristics that separate them from other diseases. First, they spread very quickly. Everything from sneezes to handshakes can spread a plague. Second, when a person becomes infected, they either die from it, or recover and be immune. Catch a plague and you probably have a maximum of 30 days left to live. Be one of the lucky ones and survive it, and the disease can never harm you again. Although your body has learned to fight it, the plague still lives in you, and you can still pass it on to other people.

The surface answer to our question is not that Europeans had better immune systems than the people of the New World, but rather that the Americas didn’t have any plagues for the explorers to bring back. There were certainly regular diseases, but there was no American Plague to carry. All of history’s infectious killers come from the Old World. But why?

European Cities

Before we dig deeper, we first have to talk about cholera. Cholera is a disease that plagues a civilization when they do a poor job of separating their drinking water from waste water. London was terrible at this, making it the cholera capital of the world. Cholera can rip through neighborhoods like wildfire, killing swaths of the population before moving on. But that’s the key: It has to move on.

In a small, isolated town, a plague like cholera cannot survive. It kills all available victims, leaving only the immune left. But after that, the plague has no where to go — it’s a fire that has burned through all of its fuel.

On the other hand, a big, populated city where hundreds of new humans are born everyday is sanctuary for plagues like cholera. With the combination of immigrants, travelers, and newborns, fresh kindling comes to the plague. With the near inexhaustible fuel, plagues become a fire that is impossible to extinguish.

The only reason cities could grow was because more people moved to them than died inside of them. Cities only started growing from their own population in the 1900s when medicine finally left its leaches and bloodletting phase and entered its soap and sanitary regulations phase, finally giving humans some tools to slow death. But before that, large cities were playgrounds for plagues; cities became a sinister sorting machine that only left the immune.

Thus, the New World didn’t have plagues because the new world didn’t have big, dense, terribly sanitized, deeply interconnected cities for plagues to thrive in. Yet, that still leaves some questions. The New World obviously wasn’t completely devoid of cities, and tribes weren’t completely isolated. Otherwise, the newly-arrived smallpox in the 1500s would never have spread. Cities are in fact only part of the puzzle; they are required for plagues, but cities don’t make the germs that start the plagues. Those germs come from something else.

Animals

Most germs don’t want to kill you for the same reason you don’t want to burn your house down: Germs live in you. Chronic diseases like leprosy are terrible diseases to contract because they are very good at making your life miserable without killing you.

Plague lethality is an accident — a misunderstanding — because the germs that cause them don’t know they’re in humans. Those germs think they’re in animals. Indeed, plagues come from animals.

Whooping cough comes from pigs, and the flu comes from birds as well as pigs. Cows alone are responsible for measles, tuberculosis, and smallpox. For the cow, these diseases are no big deal — they’re like colds for us. But when cow germs get in humans, the things they do to make the cow a little sick makes humans very sick.

Germs jumping species like this is extraordinarily rare. That’s why generations of humans can spend time around animals just fine. Being the patient zero of a new animal-to-human plague is winning a terrible lottery. But a colonial-age city raises the odds of this lottery: There used to be animals everywhere, horses transporting people, herds of livestock in the streets, open slaughterhouses, pre-refrigeration meat markets, and a river of literal human and animal excrement running through it all. A more perfect environment for diseases to jump species could hardly be imagined.

So the deeper answer is that plagues come from animals, but so rarely that you have to raise the odds by having constant interaction between human and animals, and an unsanitary environment for the plague to spread. The Old World had the necessary pieces in abundance.

But why was a city like London filled with animals like sheep, pigs, cows, and horses, and a city like Tenochtitlan was not? This brings us to the final level of the puzzle.

Domestication

Some animals can be put to human use — this is what domestication means. It happens when people use animals for more than just hunting. Forget for a moment the modern world, and go back to 10,000 BCE when tribes of early humans reached just about everywhere. If you were in one of these tribes, what local animals could you capture, tame, and successfully pen to breed?

Maybe you’re in present-day North Dakota and thinking about catching a Buffalo — an unpredictable, violent tank on hooves that can outrun you across the planes and leap over your head. And they travel in herds that can number over a thousand. Plus, you have no horses to help you because there are no horses on the entire continent.

It’s just you, a couple buddies, and stone-based tools. American Indians didn’t fail to domesticate buffalo because they couldn’t figure it out. They failed because it’s a buffalo; no one could do it. Buffalo would have been an amazing creature to put to human work back in BCE, but it’s not going to happen — humans have only barely domesticated buffalo with all our modern tools.

The New World just didn’t have good candidates for animal domestication. Almost everything big enough to be useful was too dangerous, or too agile.

On the other hand, Europe and western Asia had cows, goats, pigs, sheep, and more. These animals were comparatively begging to be domesticated. Even though wild pigs may have been difficult to capture and tame with only stone tools, at least they are relatively small and can’t crush all resistance underneath their hooves.

In The New World, the only native animal that could be domesticated was the llama. They’re better than nothing — which is probably why the biggest cities existed in South America — but they’re no cow. Ever try to manage a heard of llamas in the mountains of Peru? It is possible, but it certainly is not fun.

These might seem like cherry-picked examples because, well, aren’t there hundreds of thousands of species of animals? Yes, but when you’re stuck at the bottom of the tech tree, almost none of them can be domesticated. From the dawn of man until maritime expansion, humans domesticated maybe a baker’s dozen of unique species over the world, and even to get that high a number you need to stretch it to include honeybees and silkworms. Nice to have, but you can’t build a civilization on a foundation of honey and silk alone.

These early tribes weren’t smarter, or better at domestication. The Old World had more useful and easy animals. With dogs, herding sheep and cattle is easier. Now humans have a buddy to keep an eye on the clothing factory, and the milk and meat machine, and the plow-puller. Farming is easier, which means there’s more benefit to a non-nomadic lifestyle, which means more domestication, which means more food, which means more people, which means more density within groups of people, which means — you guessed it — plagues.

Conclusion

That is the full answer: The lack of new world animals to domesticate limited not only exposure to germs’ sources but also limited food production, which limited population growth, which limited cities, which made plagues in The New World an almost impossibility. In the Old World, exactly the reverse. Thus a continent full of plagues, and a continent devoid of it. When ships landed in the Americas for the first time, there was no American Plague to catch and bring back to Europe.

The game of civilization has nothing to do with the players, and everything to do with the map. Access to domesticated animals in numbers and diversity is the key resource to bootstrapping a complex society from nothing — and that complexity brings with it, unintentionally, a passive biological weapon devastating to outsiders. Start the game again but move the domesticable animals across the sea and history’s arrow of disease and death flows in the opposite direction.