shifting balance theory

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shifting balance theory

A theory of evolution proposed by Sewall Wright in 1931 regarding the adaptation of a species, and the cornerstone of modern evolutionary thought, which holds that adaptive evolution occurs more quickly when a population divides into uniquely adapted subpopulations followed by re-establishment of gene flow.

References in periodicals archive ?

According to this idea, genetic factors are extremely interactive, such that some combinations generate high fitness and become "peaks" on the adaptive landscape, while other combinations have low fitness and represent "valleys." Wright, in his shifting balance theory (SBT) of evolution, posited that a species becomes stuck on the local equilibrium of an adaptive peak, and can only move to the domain of attraction of a higher peak by the actions of genetic drift followed by subsequent selection (Wright 1931a, 1932; Simpson 1953; Barton and Rouhani 1987, 1993).

Unfortunately, the observations contained in this paper have one very pessimistic implication: it will be impossible to ever design an experiment that unambiguously tests the shifting balance theory sensu strictu.

Founder effects and peak shifts without genetic drift: adaptive peak shifts occur easily when environments fluctuate slightly

Phase three of Wright's shifting balance theory. Evolution 44:233-247.

Variance-induced peak shifts

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