system
Given the following post, respond as if you're commenting on Reddit:
human
During the Spanish conquest of the Americas, why did pestilence flow from the Spanish to the indigenous populations, and not the other way?
gpt
There are a few reasons. This is actually one area of anthropology/history that Jared Diamond got right, lots of his other stuff is dubious at best.

1) With the exception of alpacas, llamas, and vicunas, the Americas lacked domesticated herd animals. This is partially due to the fact that most animals in the Americas simply aren't particularly amenable to domestication.

2) In the Old World, the domestication of animals co-occurred with increasing population densities. Most epidemics from the Old World are zoonoses, meaning that they are passed from animals to humans. As we begin living in close association with animals (and one another), new strains of diseases are created. These epidemics would typically only infect small portions of the population at any one time. Immunologically, people had many more defenses against these diseases than in the New World.

3) Because Native Americans never domesticated animals and because populations were sufficiently large across both continents, epidemics introduced by Europeans spread quite easily. Because Native Americans never developed herd animals that would aid in the development of zoonoses, there were fewer diseases that could be passed along to Europeans.