Regarding the Columbian exchange, why did the ecological factors surrounding the re-connecting of the continents favor the Old World?

Question

Regarding the Columbian exchange, why did the ecological factors surrounding the re-connecting of the continents (Americas and Europe) favor the Old World (Europe)? Is there any irony in this?

I need further clarification if I'm answering this question right and if I'm going in the right direction.

As a result of the Columbian Exchange, the quality of life increased due to new agriculture being produced in Europe. However, the Old World was already immune to diseases such as smallpox and syphilis which it brought to the New World. Is this what the first part of the question is referring to, "ecological"?

Also, by the re-connecting of the continents, it introduced diseases such as smallpox and syphilis that devastated mass groups of people. Those were the same people that worked on plantations and were "slaves" in a sense. Is this what is meant by irony? This is the part which I'm most unsure how to answer because I don't see any irony?

Answer 1

As was mentioned in the comments, Guns, Germs, and Steel explains this.

Essentially, the Old World had a lot of very good animals and plants that could be domesticated. Domestication led to settled agriculture, but now you had a load of people living together in close quarters with animals and each other. This resulted in really bad diseases spreading through the population quickly. If you weren't resistant to a disease, you died, and didn't pass on your genes. As the population became more disease-resistant, the diseases had to become more virulent to survive.

The Americas did not have nearly as many good plants and animals that could be domesticated. So they had less urbanization, less contact with animals, less infections, and less resistance to disease. As soon as all these diseases came in contact with them, boom!

In terms of agriculture, old world plants and animals benefited the Americas greatly - wheat and rice are way better than corn. It's just that the people who benefited from them were European settlers, because by that point 90% of the population of Native Americans was dead.

Answer 2

Just as my personal theory, the Old World population had already been filtered through a very severe selection process, as from the time of the Greeks explorers & traders had brought back diseases from distant lands. Some of those developed into major plagues, killing off large fractions of the population. The survivors passed on robust immune systems to their descendants.