Punctuated Equilibrium

Punctuated equilibrium is the proposal that a species typically shows little evolutionary change through most of its geological history, a stable period called stasis, interrupted by rare episodes of rapid branching into new species. Paleontologists Niles Eldredge and Stephen Jay Gould introduced the idea in a landmark 1972 paper, building on Ernst Mayr's earlier work on geographic speciation and genetic homeostasis. It stands opposed to phyletic gradualism, which pictures evolutionary change as a steady, continuous transformation of a lineage over time; punctuated equilibrium instead describes long periods of morphological stability broken by short, geologically brief bursts of rapid change concentrated around speciation events.