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Embryology and the Evolutionary Synthesis: Waddington, Development and Genetics

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Embryology and the Evolutionary Synthesis: Waddington, Development and Genetics Embryology and the Evolutionary Synthesis: Waddington, Development and Genetics. by Paul Dominic Lewin. Submitted in accordance with the requirements for the degree of Doctor of Philosophy. University of Leeds Department of Philosophy. September, 1998. The candidate confirms that the work submitted is his own and that appropriate credit has been given where reference has been made to the work of others. -11- Abstract. The role of embryology, genetics and morphology witllln mid twentieth century evolution theory, is discussed in the context of the growth to dominance of natural selection as the orthodox mechanism of adaptive evolution. The unification of neo­ Mendelian heredity and neo-Darwinian selection theory, is descnbed as the core of modem synthetic neo-Darwinism as it emerged in 1930s mathematical population genetics. As selectionism strengthened witllln synthetic neo-Darwinism, embryological development was excluded from its traditional causal role in adaptive evolution witllln the "old synthesis" of Haeckelian recapitulation and neo-Lamarckian inheritance. A two-tier embryology was created, as embryology was understood to deal separately with the experimental analysis of ontogenetic development, and the historical descriptive analysis of phylogenetic lineages. Neither tier informed the other, or played any direct causal role in the mechanism of the creation of adaptive evolutionary novelty. That adaptive evolutionary mechanism was entirely the preside of natural selection. However, as the selectionist synthesis hardened in the 1940s, late nineteenth century Darwinists' concerns over the hereditary fixation of highly specific adaptive somatic modifications resurfaced. Consequently, the strategic defence of the synthetic theory against any resurgence of neo-Lamarckian heredity, involved an appeal to the principles of modem synthesis developmentalism; namely, the developmentalist syntheses of Waddington and Schmalhausen. The unforeseen implication of these moves by founding supporters of the synthetic theory, was that the disciplines upon which 1940s developmentalism rested--namely, Western chemical embryology and Soviet evolutionary morphology--did after all playa central and causal role in the mechanism of adaptive evolution. Attempts to characterise the alternative and developmentalist syntheses of Waddington and Schmalhausen as the ''missing links" to an otherwise incomplete modem synthesis, are historically evaluated. These attempts are thought to embody either a mistaken understanding of the essential nature of synthetic neo-Darwinism, or an obfuscation of the continuing issue of its synthetic adequacy. - ill- Contents. ~l>stJr~(!t •••••.••••.••••••••••••••••.••.•••••••..••••••••••••••••••••.••..••••••••••••••••.•..•••••••.•••......••.•••••••. ii. 4C:()llt4elltS ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• iii. ~Jr4e1f~(!4e ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• ~. Introduction. The Evolution of Synthetic Neo-Darwinism: The Emergence of Strong Selectionism and the ~daptationists' Dilemma ....... 1. 0.1. Evolution Before the New Synthesis: The Several Challenges to Selectionism .......................................................................................... 1. 0.2. The Foundations of Synthetic Neo-Darwinism: Development of the Mendelian-Hereditarian Research Programme ........................................ 5. 0.3. Preliminary Hardening of the Synthetic Theory: The Dismantling of the Old Evolutionary Synthesis and the Formation ofa Two Tier Embryology ......................................................................................... 11. 0.4. Further Hardening: New Synthesis Developmentalism and the Adaptationists' Dilemma ...................................................................... 16. 4C:hapter 1. The Reassessment of the Old Evolutionary Synthesis: Embryology, Genetics, and Recapitulation in the Early Modern Synthesis Years .......................................................................................... 21. 1.1. Recent Historiographical Trends in the Reassessment Of Recapitulation: Gould, Rasmussen, and Mendelian Gene Selectionist Explanation ....................................................................... 21. 1.2. Ernst Mayr, and the Resurrection of Recapitulationist Historiography in the Quarterly Review ofBiology .............................. 28. 1.2.1. Searching for Causal Explanations at the Time of the Synthesis: Holmes, Goldschmidt, and the Genetic Explanation of Recapitulation ......................................................................... 34. 1.2.2. From Invertebrate Palaeontology to Embryology and Genetics: A Biographical Sketch of Conrad Hal Waddington ...... 40. 1.2.3. Canalisation and Modern Synthesis Recapitulationism: Waddington's Elaboration of Goldschmidt's Synthesis ................ 46. 1.3. Synthesising Proximate and Ultimate Explanations: Waddington's Embryogenetical Evolutionary Theory ................................................. 56. 1.3 .1. The Cambridge Research Programme and the Embryochemical Search for the True Evocator ............................ 57. 1.3.2. Emergence of the Concept of Genetic Assimilation from the Search for the True Evocator ...................................................... 61. - iv- 1.4. Waddington, De Beer and the Haeckelian Aetiology: Evidence for Recapitulation in Modern Synthesis Embryology .................................. 65. Chapter 2. Conflicting Explanations of Adaptive Evolutionary Change: Neo-Organic Selectionism and the Adaptationist Dilemma ..................... 77. 2.1. Adaptation, Adaptive Modification, and the Modem Evolutionary Syniliesis ............................................................................................. 77. 2.1.1. Anti-Adaptationism from the Experimentalist Perspective: The Reactionary Views of Lance10t Hogben ................................ 80. 2.2. Experimental Embryology and Adaptive Evolution: Gavin de Beer's New Synthesis Embryology and the Adaptationists' Dilemma .............. 83. 2.3. The Evolutionary Significance of Adaptive Modification: Organic Selection, or th.e "Baldwin Effect"? ...................................................... 86. 2.3.1. Some Purported Examples of the Organic Selection Process ..... 90. 2.3.2. Simpson's Three-Part Definition of the Baldwin Effect.. ............ 93. 2.3.3. Simpson and Huxley on Historical Restriction: Orthoselection or Orthogenesis? ................................................. 97. 2.4. Organic Selection versus External Natural Selection: The Reactionary Darwinism of Alister Hardy ............................................ 102. 2.4.1. Hardy and Simpson Juxtaposed: Conflicting Darwinian Attitu.des to Organic Selection .................................................. 103. 2.5. The Attempted Assimilation of a Subsidiary Historical Factor: Waddington and Schmalhausen's "Broader Principles" ...................... 107. 2.5.1. Stumbling Blocks to Simpson's Defence of The Synthesis: Lloyd Morgan's Original Concept of Organic Selection ............. 113. 2.5.2. Lloyd Morgan's Principle as Pre-Mendelian Genetic Assimilation: The Hardy-Waddington Controversy .................... 115. 2.6. Neo-Organic Selection in The Soviet Union ........................................ 121. 2.6.1 Waddington's Disparagement of Soviet Neo-Organic Selectionism: the Experimental Research Work ofG. F. Gause ....................................................................................... 125. 2.6.2. Gause and Schmalhausen: The Appropriation of Stabilising Selection by Soviet Neo-Organic Selectionists .......................... 132. Chapter 3. Waddington's Alternative Synthesis: Genetic Assimilation and the Canalisation Hypothesis ............................................................. 137. 3.1. The Edinburgh Genetics Institute and the Experimental Verification of Gen.etic Assimilation ...................................................................... 137. 3.1.1. The Genetic Assimilation Research Programme in the 1950s: Waddington's Verification of the Canalisation Hypothesis ......... 142. -v- 3.1.2. Crossveinless Revisited: The Work ofK. G. Bateman on Four Venation Phenocopies and the Questionable Role of Canalisation .............................................................................. 148. 3.1.3. The Assimilation of a Character of Macro-Evolutionary Magnitude: Waddington's Acceptance of Gausian Stabilising Selection ................................................................................... 159. 3.2. Orthodox Genetic Support for the Canalisation Hypothesis: Lerner, Mather, and Quantitative Genetics in the 1940s and 1950s ................. 163. 3.3. Private Support and Public Rejection: Dobzhansky and the Denial of Waddington's Genetic Assimilation .................................................... 179. 3.3.1. A Recent Historiographical Assessment of the Waddington versus Schmalhausen Controversy ............................................. 184. Chapter 4. Stabilising Selection Versus Canalising Selection: The Competing Evolutionary Syntheses of C. H. Waddington and I. I. Schm.alhausen ........................................................................................... 187. 4.1. Introduction: The Structure and Arguments of Schmalhausen's Factors ofEvolution: The Theory ofStabilising Selection ................. 187. 4.2. The Nature and Action
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