Red Queen hypotheses maintain that biotic interactions are the most important drivers of evolutionary change, whereas Court Jester hypotheses regard physical-environmental perturbations, such as climate change, as most important. Tests for the biotic effects of climate change that are conducted on too large a geographic scale can falsely reject the Court Jester because climate is so complex its manifestation is in opposite directions in different geographic areas. Consequently, faunal responses vary from place to place, and lumping of data from different climate zones averages out any local faunal responses. Likewise, tests that are conducted at inappropriate temporal scales will not be effective at distinguishing between the Red Queen and Court Jester.
A test at a temporal and geographic scale that takes the above considerations into account suggests a biotic response of mammals to a climatic warming event in the northern Rocky Mountains 18.5–14.0 Ma (the late-Early Miocene climatic optimum). During the environmental perturbation, mammalian species richness possibly increased, faunal turnover was pronounced, and taxa adapted to warm, arid environments became more abundant in numbers of species and density of individuals. The data are consistent with environmental change—the Court Jester—driving evolutionary change at sub-continental spatial scales and temporal scales that exceed typical Milankovitch oscillations. The Red Queen may be active at smaller temporal and geographic scales.