Portal:Evolutionary biology/Selected article/9
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Punctuated equilibrium is a theory of evolutionary biology. Its principle is that most sexually reproducing populations experience little change for most of their geological history, and that when phenotypic evolution does occur, it is localized in rare, rapid events of branching speciation (called cladogenesis). Punctuated equilibrium is commonly contrasted against the theory of phyletic gradualism, which states that evolution generally 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 degree of gradualism championed by Charles Darwin was virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species.
