PUNCTUATED EQUILIBRIUM

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PUNCTUATED EQUILIBRIUM

Graph of Gradual Evolution Punctuated Equilibrium Some biologists claim that most evolutionary change takes place as a result of a series of very small changes (‘gradualism’). Graph of Gradual Evolution http://anthro.palomar.edu/synthetic/images/graph_of_phyletic_gradualism.gif

Others claim that there were long periods with no or little change and then short periods of rapid change (‘punctuated equilibrium). Punctuated equilibrium predicts that a lot (rapid) of evolutionary change takes place in short periods of time tied to speciation events

THE PUNCTUATED EQUILIBRIUM MODEL Stephen J Gould Gould and Eldredge formulated this model (1972) They observed that the fossil record gives a different picture of evolution They claim that there were long periods of stasis (4-10 million years) involving little evolutionary change Then occasional rapid formation of new species (5,000 - 50,000 years). Niles Eldredge © 2008 Paul Billiet ODWS

Two models

Punctuated Equilibrium (CAPSp.61) Punctuated equilibrium is an important but often-misinterpreted model of how evolutionary change happens. Punctuated equilibrium does not: Suggest that Darwin's theory of evolution by natural selection is wrong. Mean that the central conclusion of evolutionary theory, that life is old and organisms share a common ancestor, no longer holds. Imply that evolution only happens in rapid bursts.

There are different phases in Evolution Stasis (Gradualism) Rapid change (Punctuated equilibrium) http://anthro.palomar.edu/synthetic/images/graph_of_punctuated_equilibrium_2.gif

Punctuated equilibrium Living ,dying and being fossilized - little observable evolution

Punctuated equilibrium Isolation – lake forms and isolate small population

Punctuated equilibrium