ESHS/HSS Annual Meeting

The ‘Missing’ Chapter of the Evolutionary Synthesis: Sewall Wright’s Hierarchical Integration of Evolution and Development

• In Event: Evolutionary Histories 1

English Abstract

According to a prevailing historical narrative, the architects of the Evolutionary Synthesis ignored the relevance of organismal development to evolution. This paper demonstrates that, when it comes to Sewall Wright, the prevailing narrative is mistaken. Wright made a serious attempt to integrate evolution and development in his landmark 1931 paper, “Evolution in Mendelian Populations.” Wright’s stated project was to determine (1) the conditions at each level of the hierarchy of biological organization—gene, cell, organism, deme, etc.—that promote the genetic homogeneity or genetic heterogeneity of a species, and (2) how these conditions achieve a balance that enables a species to undergo cumulative adaptive change. From his studies of physiological and developmental genetics in mammals, Wright came to appreciate the intricacies of gene interactions during development and the sensitivity of development to environmental variation. These empirical generalizations directly and substantively shaped his distinctive views of evolution, to include the shifting balance theory and (later) the adaptive landscape. Two mutually-reinforcing hypotheses are presented and motivated in this paper to explain how such an important chapter of the Evolutionary Synthesis could have gone missing. First, there is a lack of systematicity and clarity in certain aspects of Wright’s work, especially those relating to hierarchies. Second, Wright occupies an awkward position in the historiography of the Evolutionary Synthesis, which has left neither defenders nor critics of the Synthesis with sufficient motivation to reconstruct Wright’s nuanced and fragmented project of integrating evolution and development.

Author

• Zachary Mayne, University of Pittsburgh