Using microbial microcosms to study host-parasite coevolution

Microbial microcosm experiments with bacteria and their viral parasites allow us to observe host-parasite coevolution in action. Laboratory populations of microbes evolve rapidly, thanks to their short generation times and huge population sizes. By taking advantage of a "living fossil record" stored in the laboratory freezer, we can directly compare the fitness of hosts and parasites with their actual evolutionary ancestors. Such experiments demonstrate that host-parasite coevolution is an important evolutionary force and a cause of strong and divergent natural selection.