Punctuated equilibrium (sometimes referred to as punctuated equilibria) is a theory in evolutionary biology, which states that most sexually reproducing species will show little change for most of their geological history. When phenotypic evolution occurs, it is localized in rare events of branching speciation (called cladogenesis), and occurs relatively quickly compared to the species' full and stable duration on earth.
Punctuated equilibrium is commonly contrasted against the theory of phyletic gradualism, which states that most evolution occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis). In this view evolution is seen as generally smooth and continuous.
In 1972 paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing this idea. Their paper was built upon Ernst Mayr's theory of geographic speciation, I. Michael Lerner's theories of developmental and genetic homeostasis, as well as their own empirical research. Eldredge and Gould proposed that the gradualism predicted by Charles Darwin was virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species.