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
Ecological-evolutionary theory Ecological-evolutionary theory Ecological-evolutionary theory (EET) is a sociological theory of sociocultural evolution that attempts to explain the origin and changes of society and culture. Key elements focus on the importance of natural environment and technological change. EET has been described as a theory of social stratification, as it analyzes how stratification has changed through time across different societies. It also has been viewed as a synthesis of the structural functionalism and conflict theory. Proposed by Gerhard Lenski, the theory perhaps is best articulated in his book, "Ecological-Evolutionary Theory: Principles and Applications" (2005). His major collaborators, Jean Lenski and Patrick Nolan,