As I mentioned, not all diseases are easily explainable in evolutionary terms. We might argue that a disease, like malaria, reflects balancing selection (with survival penalty of sickle cell counteracted by the benefit of surviving malaria) but it is important to consider that many disease traits have no survival benefit. While balancing selection explains some diseases, and antagonistic pleiotropy might explain others, it is important to note that all organisms die, and some diseases lack a good evolutionary explanation.
With that caveat in mind, my view is that evolution can inform most human illnesses, either in terms of phylogenetics, constraints, host-pathogen arms races, or evolutionary concepts of aging. Be sure to refresh your memory on all of these by reading this post again:
Read http://evolutionmedicine.wordpress.com/categories-of-evolutionary-medicine-hypotheses/ before your presentation.
JA
