What is the name of the theory that evolution proceeds in rapid bursts separated by long stable periods?

The theory that evolution proceeds in rapid bursts separated by long stable periods is called punctuated equilibrium. It proposes that species often show little morphological change for long stretches of geological time, followed by relatively rapid episodes of evolutionary change.

Paleontologists Niles Eldredge and Stephen Jay Gould formally presented the theory in 1972. Their model was based on patterns in the fossil record, where species can appear stable for millions of years and then seem to change quickly, often as new species branch from relatively small, geographically isolated populations.

Punctuated equilibrium is commonly contrasted with phyletic gradualism, which describes evolution as a steadier accumulation of small changes within a single lineage. The contrast is about evolutionary tempo and pattern, not whether mutation, natural selection, or inheritance operate. Evolutionary change can occur through both gradual and relatively rapid processes.

The theory does not mean that organisms transform overnight or that every species evolves in dramatic bursts. “Rapid” is usually rapid in geological terms, and the pattern may partly reflect gaps in fossil preservation. Gradual change is also documented, so many biologists treat the two patterns as complementary rather than mutually exclusive.