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Evolutionary Stasis

Evolutionary stasis occurs when one or many species remain the same genetically with little change over long geological periods of time; periods of evolutionary stasis are often punctuated by periods of energetic evolution. This pattern is referred to as punctuated equilibrium. Species that have remained unchanged for hundreds of millions of years include the cyanobacteria, coelacanth, the lungfish, and some species of crocodiles.

The most likely reason for evolutionary stasis is a stable long-term environment. Motivations for evolutionary change normally come in the form of cataclysms that change the world's climate or the introduction of a disease or new predator. Absent these environmental changes, there is no pressure on the species to adapt.

A few times in history cataclysmic events are known to have caused vast die-offs, generally when the Earth was hit with a comet or a large meteor. These events are thought to have spurred rapid adaptation and speciation. However, there is no certainty regarding the mechanisms of rapid adaptation and subsequent speciation.

Some of the things that encourage evolutionary stasis include flexible adaptation to a wide range of environments, a lack of predators, the species' being cut off from other environments, and a lack of change in the native environment.

Web Resources On Evolutionary Stasis

Stasis and Evolution
Speciational Evolution or Punctuated Equilibria

Book Resources On Evolutionary Stasis

Evolutionary Dynamics : Exploring the Interplay of Selection, Accident, Neutrality, and Function by Crutchfield & Schuster
Darwinian Dynamics by Richard E. Michod

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