Interesting question. I found this: http://www.todayifoundout.com/index.php/2014/03/native-ameri...

Fun tidbit:

> But contrary to popular belief, it wasn’t all one sided. It’s believed that one Native American disease did slip on to the European ships and sailed onward to Europe doing some major damage in the process. That disease was syphilis.

It is one theory, but things are not completely clear: https://en.wikipedia.org/wiki/History_of_syphilis#Origin

While not everyone is a fan of Jared Diamond, see: https://www.enotes.com/topics/guns-germs-steel

Infectious diseases often arise when humans live in large groups with their animals from which a lot of the diseases originate.

My uneducated guess is that the Europeans lived in much larger communities (in Europe), which is a much better breeding ground for disease. This meant they were much more full of disease than the native Americans.

Another uneducated guess is that this is why your pet <insert species name here> doesn't often get sick - they have much less contact with other <insert species name here>s than you do with other humans, contributing to less and slower spread of disease.

Please could a pathologist jump in and enlighten me?

> My uneducated guess is that the Europeans lived in much larger communities (in Europe), which is a much better breeding ground for disease

Not a bad guess, but completely wrong. The cities of Mesoamerica or the Andes or the Mississippian culture of North America would have dwarfed most European cities, before they were ravaged by disease.

The best explanation I have seen is that almost all domesticable animals in the New World were exterminated early, and so there wasn't anywhere near the cross-species disease potential in the Americas. Old Worlders had domesticated horses, goats, sheep, pigs, cows, a wide array of fowl, camels, dogs, cats, etc, etc. In the Americas, there were turkeys, ducks, llamas & alpacas, and guinea pigs - and not all of those in any one place.

Fascinating! Thanks

There is a great video by CGP Grey which covers exactly that topic: https://youtu.be/JEYh5WACqEk

Syphilis was taken back to Europe and killed millions.

This was less likely for two reasons. First, the old world had dense concentrations of people for much longer, which domesticated many different diseases, making them childhood annoyances. And second, we spent much longer living in Africa, and co-evolved with diseases like malaria, which but left these behind when emigrating via Alaska. (Edit: I forgot syphilis, which is a likely candidate for a new-world disease. But certainly there were fewer.)

East-west contact within Eurasia of course did bring some serious diseases to the West, to which people had no resistance. Plague in the 14thC, cholera in the 19th. (Did any similar diseases arrive in the East? I can't think of any.)

Two reasons stand out:

First, Europeans lived in appalling filth. The sanitary details are well documented elsewhere, the most telling point being that cities of Western Europe only gained population by migration, not internal growth, so bad were the epidemics. It was a millennium-long germ warfare lab.

Second, Europeans and Asians lived alongside livestock such as pigs and fowl, and also rats, all notorious breeders of diseases that humans can catch. The interplay of illnesses between humans and animals fed the epidemics.

For one thing, there are accounts of Europeans deliberately exposing the natives to diseases. It wasn't just a natural unfortunate occurance.

There are plural accounts, but there is only a single documented case historians have evidence for of the British at Fort Pitt deliberately using infected items from their infirmary.

I wonder how they thought of it. I don't think germ theory was common knowledge at the time.

The New World lacked domesticated animals.

https://youtu.be/JEYh5WACqEk

Lung cancer.