Shifting balance theory Shifting balance theory The shifting balance theory is a theory of evolution proposed in 1932 by Sewall Wright, suggesting that adaptive evolution may proceed most quickly when a population divides into subpopulations with restricted gene flow. The name of the theory is borrowed from Wright's metaphor of fitness landscapes (evolutionary landscapes), attempting to explain how a population may move across an adaptive valley to a higher adaptive peak. According to the theory, this movement occurs in three steps: Although shifting balance theory has been influential in evolutionary biology, inspiring the theories of quantum evolution and punctuated equilibrium, little empirical evidence
Evolution as fact and theory their various forms to provide explanations of observed patterns in relation to their evolutionary history and biology. The neutral theory of molecular evolution is used to study evolution as a null model against which tests for natural selection can be applied. The following sections provide specific quotable references from evolutionary biologists and philosophers of science demonstrating some of the different perspectives on evolution as fact and theory. "Fact" is commonly used to refer to the observable changes in organisms' traits over generations while the word "theory" is reserved for the mechanisms that cause these changes: Other commentators – focusing on