punctuated equilibrium model

Evolutionary theory developed by Niles Eldredge and US palaeontologist Stephen Jay Gould in 1972 to explain discontinuities in the fossil record. It claims that evolution continues through periods of rapid change alternating with periods of relative stability (stasis), and that the appearance of new lineages is a separate process from the gradual evolution of adaptive changes within a species.

The pattern of stasis and more rapid change is now widely accepted, but the second part of the theory remains unsubstantiated.

The turnover pulse hypothesis of US biologist Elisabeth Vrba postulates that the periods of rapid evolutionary change are triggered by environmental changes, particularly changes in climate.