"In the world our human immune system evolved in hundreds of thousands of years ago, infectious diseases could not become a major problem because, with a few exceptions, when you survive an infectious disease, you usually don’t get it again. Either it kills you or it leaves you completely immune to it for the rest of your life. For the vast majority of human history our species lived in small tribes that were spread thin and, for all intents and purposes, pretty isolated from each other. An infectious disease simply could not become a dangerous threat and establish itself in our ancestors effectively. Because if it infected a tribe, it would infect every available person in no time and then die off because there would be no one left to jump over. So our evolution did not really have to consider these sorts of pathogens that much.

"As we became farmers and city dwellers our lifestyle changed forever—and so did the diseases that targeted us. Living close together created a perfect breeding ground for infectious diseases. Suddenly, in evolutionary terms, there were hundreds or even thousands of victims to infect. As our ancestors were not aware of the nature of microorganisms or even basic hygiene and they did not yet possess tools like soap and indoor plumbing, there was not much they could do—on the contrary, their lack of understanding made things worse.

"And when they began domesticating and living together with animals in close quarters, often even sleeping in the same rooms, some pathogens jumped over. Our new lifestyle turned out to be the perfect environment for the pathogens of our new animal friends, to adapt to humans and vice versa. As a consequence, virtually every infectious disease we know today arose in the last ten thousand years. From cholera, smallpox, measles, influenza, and the common cold to chicken pox."

Immune by Philipp Dettmer

This is not convincing.

Our immune systems were evolving 100 thousand years ago, and they still are now.

If we weren't able to handle new diseases, everyone would have died from covid, not some percent of a percent. Our immune systems are very very capable for handling pathogens

The book has extensive references.

I hope you've brought yours.

https://kurzgesagt.org/immune-book-sources/

https://www.philippdettmer.net/immune

So does Guns, Germs, and Steel and Sapiens, and Dawn of Everything and so does 1491 - and for all they do touch on disease what I've said comports with them.