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
Zero-Force Evolutionary Law Zero-Force Evolutionary Law The Zero-Force Evolutionary Law, or ZFEL, is a theory proposed by Robert Brandon and Dan McShea regarding the evolution of diversity and complexity. Brandon and McShea define diversity and complexity in terms of variation, diversity being variation between organisms and complexity being variation among parts within an organism. McShea had previously defined a part as "a system that is both integrated internally and isolated from its surround," giving the digestive tract, epidermis, and skeleton, as examples. As an analogue to the theory of relativity, the theory has a special and general formulation. The special formulation states "in