There are relatively few fungi that invade the bodies of the only two kinds of warm-blooded creatures: mammals and birds. A new theory suggests that we are warm-blooded - a very expensive evolutionary trick - in order to kill off most fungi.
This is one of the best New Scientist articles I've read in a while, not only for its well-written depiction of the process of discovering this new possibility, but also for its sidebar of evolutionary oddities at the end of the article.
Killer fungi made us hot-blooded New Scientist