Our second main goal is to review the evidence from biomedically important infectious diseases of humans, describing how the success of various disease agents may be commonly considered in light of their genetic and/or environmental robustness. The importance of robustness has been discussed in the context of noninfectious diseases such as cancers and metabolic syndromes. 17, 18 Here we focus particularly on infectious disease systems: the evolution of antibiotic resistance in bacteria, influenza virus host shifts, and malaria parasite invasion. A review of these studies seeks to further demonstrate the broad importance of robustness to theories of biological systems, and the evolution of infectious disease.