From Guns, Germs, and Steel, explain why the exchange of diseases from the old world and the new world was so one-sided?
The reason why the exchange of disease was so one-sided was that Europeans lived in closer proximity to each other and diseases such as smallpox could only be caught once. Smallpox epidemics raged through England every ten years or so, but the disease was mainly fatal to young children and the elderly. It was possible for a young adult to catch it and at worst only suffer a few smallpox scars. These people could then become disease carriers and spread it to Native Americans who had never been in contact with the disease before, thus having no immunity. Since smallpox adapts so quickly and the immune systems of many Native Americans were quite similar to one another, it was only a matter of time before one smallpox victim could infect an entire tribe. Exposure to cowpox also prevented many Europeans from contracting smallpox--the Native Americans would not have cattle until whites arrived in their area.
The exchange of diseases was so one-sided because the people of the Americas did not have many large, domesticated animals while the people of the Old World had such things as pigs and horses and cows.
This matters because of the fact that the diseases that killed the natives of the Americas were generally ones like smallpox that had come from the domesticated animals that were kept by people in the Old World. The Old World had been luckier so they had domesticated animals. The domesticated animals gave them the germs that killed off the people of the New World.