Red Queen Hypothesis.--The "Red Queen" hypothesis is used to describe two similar ideas, which are both based on coevolution. The original idea is that coevolution could lead to situations for which the probability of extinction is relatively constant over millions of years (Van Valen 1973). The gist of the idea is that, in tightly coevolved interactions, evolutionary change by one species (e.g., a prey or host) could lead to extinction of other species (e.g. a predator or parasite), and that the probability of such changes might be reasonably independent of species age. Van Valen named the idea "the Red Queen hypothesis," because, under this view, species had to "run" (evolve) in order to stay in the same place (extant).