Research area A focuses on infectious diseases caused by microorganisms that are prime candidates for rapid evolutionary change. It has long been recognised that pathogens may strongly affect host population dynamics and evolution, and accordingly, important mathematical models have been developed since the 1970s. Nevertheless, only recently the biomedical implications of evolutionary processes in host-pathogen interactions have been fully recognised and the tools have become available for studying such processes in genetic and genomic detail. It became clear that basic processes of pathogen evolution and even host-pathogen coevolution can be studied with experimentally accessible systems in the laboratory and that results of such studies are of relevance also for human pathogens. Research area A addresses questions of rapid adaptation and the role of environmental and host-derived selection pressures in viruses and bacteria within the following projects: