Punctuated equilibrium

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Punctuated equilibrium is a theory in evolutionary biology which proposes that most sexually reproducing species will experience little net evolutionary change for most of their geological history, remaining in an extended state called stasis. Punctuated equilibrium also proposes that stasis is broken by rare events of large net change, characterised by rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which species split into two distinct species, rather than one species gradually transforming into another. Thus, "punctuated equilibria is a model for discontinuous tempos of change (in) the process of speciation and the deployment of species in geological time."[1]

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 theory and called it punctuated equilibria.[2] Their paper built upon Ernst Mayr's theory of geographic speciation,[3] I. Michael Lerner's theories of developmental and genetic homeostasis,[4] as well as their own empirical research.[5][6] Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species.

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