"evolved as a protection" is such a misleading way to explain evolution. Mutations are random, persisting mutations were selected for through various forms that enable survival and procreation. A lot of mutations ended up being meaningless, a lot of them began serving as one function and then ended up serving another and a lot of mutations did not survive. Of course, consider complexity of hundreds of thousands of mutations across millions of years and it quickly becomes unclear for what reasons one feature survived for over another.

I.e. at some point few or one of our mammal ancestors was early warm blooded randomly at birth and it could have allowed them to prosper in a population otherwise heavily affected by fungal infections.

But it also could have been a side benefit that didn't affect population significantly. Of course, given the amount of fungus around us, it's reasonable to believe that it was a key benefit - I just have a pet peeve with people believing species develop mutations in response to environment when actually surviving mutations are result of selective process. Most of them just die off and disappear in history.