system
Given the following post, respond as if you're commenting on Reddit:
human
Why didn't the Europeans acquire new diseases when they explored the Americas?

Disease was one of the biggest causes of death for most of the Native Americans, so why didn't the Europeans encounter diseases that they could have carried back to Europe and caused another epidemic.
gpt
I believe this is related to the relative levels of development of the societies. In the stage of transition from a hunter-gatherer lifestyle to one of farming and domestication, humans become susceptible to epidemic disease, because they are living closer together, and also in close proximity to animal vectors. A lot of early epidemic disease, for example smallpox and measles developed from diseases which originally infected domestic animals. The Europeans had already gone through this stage when they arrived in the Americas, and so had developed resistance to these kinds of illnesses. The Native Americans had not and so had no resistance to the imported diseases, and local ones that might affect the Europeans had not emerged.