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Comment by jgilias | Hacker News Reader

A serious question. Why didn't the opposite happen? Why wouldn't the arriving Europeans drop like flies after encountering foreign pathogens thus killing off the entire conquest?

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CGP Grey has a interesting video on this:

Americapox: The Missing Plague - YouTube https://m.youtube.com/watch?v=JEYh5WACqEk

tl;dr: The Americas had very few animals suitable for domestication, and so Americans had less animal-to-human spread of diseases.

Well there was/is syphilis which is theorized to originate in the Americas and killed millions when it broke out in Europe. Apparently was more also infectious in the beginning and only turned into an STD later-on.

But Eurasia had a far larger landmass and population so there was a larger chance for nasty diseases to develop.

Most very dangerous transmittable diseases (like covid, TB, small pox), all moved from animals to human. Virus' in general evolve to not be particularly deadly, they can't spread if they kill the host. So the ones that do kill you, basically jump from one species to ours, and turn out to be very deadly. Bovine TB isn't a huge deal for cows, in the same way a cold isn't for us, but it'll really mess a person up.

Eurasia had much better options for domesticating a wide variety animals, so in general people lived in closer proximity to lots of animals, and generally unhygienic to boot. Which all lead to more diseases spreading over.

The America's only had a few domesticated species that deadly viruses could hop from.

It's really a function of the amount of species that can be domesticated, the Americas has only few of them. Domesticated species end up living in close proximity to humans and create a perfect environment for disease.

There were diseases in the Americas, they were deadly too. One thing to consider is how they spread and if they are contagious between humans. Malaria is horrible, but you don't catch it from other people, pox on the other hand will spread between humans. This is just one example. Being mostly exposed to nasty diseases that are not contagious will lead a culture to have different behaviour when dealing with the sick. These practices will often involve taking close care of the sick. Such practices will prove horrible for dealing with highly lethal contagious diseases from Europe.

(Not an expert, I just happen to have read a fair bit about the topic, grain of salt highly recommended)

Cities. Very deadly pandemics generally come from diseases that jump from another species to humans.

It is not advantageous for a virus to have a very high lethality, for any parasite there is no advantage in killing large numbers of your host. It's the diseases that are kind of new to the host that can be more lethal.

This jump of a disease from one species to another happens more easily when there is a lot of close contact between them. Large cities where humans lived with animals, and in not-very sanitary conditions, were a perfect ground for this.

In America cities appear to be less dense, and animal husbandry was way less extended (AFAIK, llamas and alpacas are the only animals domesticated in America).

"Guns, germs snd Steel" book makes an argument that European population evolved higher levels of immunity to the pathogens because of population density, especially in the cities.

Population density and wars for land and resources, book argues, also propelled the development of warfare tech ("guns and steel")

The book mentions population density but quickly discards population density as the primary factor. Instead it focuses on domesticated animals. Eurasians had many domesticated animals and often lived in close quarters with them. The New World had an extreme paucity of domesticable animals and therefore much less exposure to disease vectors and therefore no major disease capable of wiping out populations. (pg 212-213)

Yes, that is key! The lack of beasts of burden and domesticated animals in the Americas. People often overlook this when talking about "how could a whole continent be wiped out by pox"

Didn't Tenochtitlan have a famously-large population for the era?

I read somewhere that disease prevented European colonizers from overtaking larger parts of southern Africa. I cannot remember the source though.

On average Europeans have less genetic resistance to malaria than Africans.

https://www.sciencedaily.com/releases/2017/05/170518143819.h...

I read that it was because Europeans lived in wider settlement so they were more exposed to serious pathogens and had the opportunity to develop immunity. When they met society that lived in scarce group, they exposed them too quickly, which resulted in mass deaths.

Maybe a smaller pool of diseases: nasty ones like pox, black death and cholera were from Europe and nearby parts of Africa and Asia. Accumulated "wealth" in the immune system.

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