Apicomplexa and microsporidia are two groups of parasites that infect a broad range of animals, including humans. Apicomplexa cause serious diseases such as malaria and encephalitis. Traditionally, microsporidia were not prevalent among humans. However, microsporidia are increasingly becoming a problem in people with impaired immune systems. The relationships of these parasites to other organisms and how they evolved are not clearly understood. Yet recent molecular studies have revealed surprising evolutionary histories for both groups of parasites. Apicomplexa evolved from an alga, an unusual origin for a parasite. Microsporidia were originally believed to be simple, single-celled organisms that were not highly evolved. But we now know that microsporidia have evolved from fungi. I am studying the evolution and biology of apicomplexa and microsporidia to learn how they developed into parasites and how they function. This research may uncover weaknesses in the parasites that can be exploited to develop new treatments for disease involving herbicides or fungicides that would not have been considered earlier.