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
The Structure of Evolutionary Theory explores the concept of "hierarchy" in the action of evolution (the idea that evolution may act on more than one unit simultaneously, as opposed to only acting upon individual organisms). In the arena of "efficacy" he explores the forces beside natural selection that have been considered in evolutionary theory. In the arena of "scope" he considers the relevance of natural selection to the larger scale patterns of life. Gould was motivated to write the book by contrasting the opinions of Darwin and Hugh Falconer about the future of Darwinism. Part I of the book focuses on the early history of