The turnover-pulse hypothesis, formulated by paleontologist Elisabeth Vrba, suggests that major changes to the climate or ecosystem often result in a period of rapid extinction and high turnover of new species (a "pulse") across multiple different lineages.
Vrba proposes that changes in the climate, through their effect on the physical environment, result in the "division of [animal] populations into geographically and genetically isolated groups", which subsequently evolve into separate species.
Vrba argued that the mammalian fauna of East Africa experienced a rapid burst of extinction and speciation between 2.8Ma and 2.5Ma, caused by a large fluctuation in temperature.
[5] The main opposing viewpoint is the Red Queen hypothesis, proposed by Leigh Van Valen, which holds that extinction occurs in a constant turnover, instead of pulses.
[9][10] Suggested explanations for the discrepancy include that "variations in fossil abundance through time skewed Vrba's data, creating a false peak" or that the "Turkana rift valley—which held a river bounded by woodland at this time—was buffered from the dramatic climatic shifts".