Punctuated equilibrium

Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and rapid (on a geologic time scale) events of branching speciation.

Overview

Punctuated equilibrium is commonly contrasted against phyletic gradualism, the idea that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous.

In 1972, Stephen Jay Gould and Niles Eldredge first proposed the theory of punctuated equilibrium. They argued that nearly every evolutionary change occurs during speciation.

Development of the theory

The concept of punctuated equilibrium originated in the work of Mayr in 1954 and was subsequently taken up by Stephen Jay Gould and Niles Eldredge in 1972. They used the term to describe the evolutionary dynamics of some groups of organisms. They argued 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.

Criticism and acceptance

The concept of punctuated equilibrium has been a matter of debate within the scientific community. Some scientists argue that it is a significant departure from the mainstream view of evolution as a slow, gradual process, while others argue that the idea is a minor revision, or simply a recharacterization of the mainstream view. Despite the controversy, punctuated equilibrium has become a widely accepted concept within evolutionary biology.

See also

• Evolutionary biology
• Phyletic gradualism
• Speciation
• Stasis
• Stephen Jay Gould
• Niles Eldredge

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