The evolution of phenotypic plasticity: Genealogy of a debate in genetics Antonine Nicoglou * IHPST Paris, CNRS, University of Paris 1, ENS,13 rue du Four, 75006 Paris, France article info Article history: Available online 28 January 2015 Keywords: Phenotypic plasticity Evolution Anthony Bradshaw Quantitative genetics Adaptive plasticity Extended synthesis abstract The paper describes the context and the origin of a particular debate that concerns the evolution of phenotypic plasticity. In 1965, British biologist A. D. Bradshaw proposed a widely cited model intended to explain the evolution of norms of reaction, based on his studies of plant populations. Bradshaw’s model went beyond the notion of the “adaptive norm of reaction” discussed before him by Dobzhansky and Schmalhausen by suggesting that “plasticity”dthe ability of a phenotype to be modified by the envi- ronmentdshould be genetically determined. To prove Bradshaw’s hypothesis, it became necessary for some authors to identify the pressures exerted by natural selection on phenotypic plasticity in particular traits, and thus to model its evolution. In this paper, I contrast two different views, based on quantitative genetic models, proposed in the mid-1980s: Russell Lande and Sara Via’s conception of phenotypic plasticity, which assumes that the evolution of plasticity is linked to the evolution of the plastic trait itself, and Samuel Scheiner and Richard Lyman’s view, which assumes that the evolution of plasticity is independent from the evolution of the trait. I show how the origin of this specific debate, and different assumptions about the evolution of phenotypic plasticity, depended on Bradshaw’s definition of plas- ticity and the context of quantitative genetics. Ó 2015 Elsevier Ltd. All rights reserved. When citing this paper, please use the full journal title Studies in History and Philosophy of Biological and Biomedical Sciences 1. Introduction Since the end of 1970s, some biologists (e.g., Coleman, 1980; Gould, 1977; Hamburger, 1980; Lauder, 1982; Wallace, 1986) have started to question the adequacy of the genocentric conception of the Modern Synthesisdwhich brought together Mendelian ge- netics, and evolution through population genetics (Huxley, Pigliucci, & Müller, 1942)din explaining the evolution of pheno- typic traits, suggesting that developmental issues should also be included in the synthesis (Gilbert, Opitz, & Raff, 1996). More recently, some authors have stressed that phenotypic plasticity should be seen as one important element in an extended synthesis of evolution including these developmental issues (see, Pigliucci & Müller, 2010). The present paper comes back on a precise controversy in the history of phenotypic plasticity in biology, which is a debate in the 1980s between two representative views (among others)dthese of Via & Lande and Scheiner & Lymandconcerning the evolution of phenotypic plasticity. The aim of the paper is to lay the groundwork for a genealogy of phenotypic plasticity and to show that the notion was defined and discussed since a long time before the 2010s, and that it adopted a specific meaning in the emerging field of quantitative genetics. Through a clarification of the origins and the basis of a specific debate concerning the evo- lution of phenotypic plasticity that occurred in the 1980s, the purpose here is to enlighten some of the implicit ideas, which used to be associated with the notion of plasticity at that time, and to show the reasons why it remains difficult to associate the notion with something different from the Modern Synthesis. In 1965, Anthony D. Bradshaw (1926e2008) published an article entitled The Evolutionary Significance of Phenotypic Plasticity in Plants. In the article, he proposed for the first time a model intended to explain the evolution of norms of reaction mainly based on his * Tel.: þ33 6 81 44 64 25. E-mail address: antoninenico@gmail.com. Contents lists available at ScienceDirect Studies in History and Philosophy of Biological and Biomedical Sciences journal homepage: www.elsevier.com/locate/shpsc http://dx.doi.org/10.1016/j.shpsc.2015.01.003 1369-8486/Ó 2015 Elsevier Ltd. All rights reserved. Studies in History and Philosophy of Biological and Biomedical Sciences 50 (2015) 67e76