Wright’s Shifting Balance Theory and Factors Affecting the Probability of Peak Shifts

Abstract

Sewall Wright's shifting balance theory remains controversial in part because it is what would today be called a complex systems model that was never developed beyond that of a metaphor. A key component of this theory, the adaptive landscape, has become an important element in population genetics and evolutionary theory. This chapter explores the original metaphor of the adaptive landscape can be modified to make it a usable concept. It suggests that it is useful to consider the landscape to be a very high dimensional space that is conceptually helpful but of little practical use. The high-dimensional landscape potentially includes all aspects of the genotype and phenotype, including aspects of the social and physical environment that affect the phenotype. This broad conceptual visualization of an adaptive landscape is concordant with the diverse uses of this metaphor in evolutionary theory if we consider adaptive landscapes with only a few dimensions to be projections of the high dimension landscape on to the subset that are being used. This modified view of adaptive landscapes is used to discuss Wright's shifting balance theory and how it can be changed to accommodate modern experimental and theoretical findings.