Punctuated equilibrium is the evolutionary model coined by Stephen Jay Gould and Niles Eldredge in 1972.
The model proposes that species often remain relatively unchanged for long periods, called stasis, followed by comparatively brief episodes of rapid evolutionary change. Gould and Eldredge developed the idea partly from patterns they observed in the fossil record, especially among fossilized marine organisms.
Punctuated equilibrium does not claim that evolution always happens suddenly or that gradual change never occurs. It contrasts with phyletic gradualism, which emphasizes slow, continuous transformation within a lineage. In the punctuated model, rapid change may occur when a small, geographically isolated population becomes separated from a larger one and evolves under different selection pressures.
The term is frequently misunderstood as meaning evolution happens in a single generation. Instead, “rapid” is relative to geological time: thousands of generations can still appear brief in a fossil sequence. The model remains an important discussion of evolutionary tempo and pattern.