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University of Cincinnati UNIVERSITY OF CINCINNATI Date: 14-May-2010 I, Lindsay R Craig , hereby submit this original work as part of the requirements for the degree of: Doctor of Philosophy in Philosophy It is entitled: Scientific Change in Evolutionary Biology: Evo-Devo and the Developmental Synthesis Student Signature: Lindsay R Craig This work and its defense approved by: Committee Chair: Robert Skipper, PhD Robert Skipper, PhD 6/6/2010 690 Scientific Change in Evolutionary Biology: Evo-Devo and the Developmental Synthesis A dissertation submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Philosophy of the College of Arts and Sciences by Lindsay R. Craig B.A. Butler University M.A. University of Cincinnati May 2010 Advisory Committee: Associate Professor Robert Skipper, Jr., Chair/Advisor Professor Emeritus Richard M. Burian Assistant Professor Koffi N. Maglo Professor Robert C. Richardson Abstract Although the current episode of scientific change in the study of evolution, the Developmental Synthesis as I will call it, has attracted the attention of several philosophers, historians, and biologists, important questions regarding the motivation for and structure of the new synthesis are currently unanswered. The thesis of this dissertation is that the Developmental Synthesis is a two-phase multi-field integration motivated by the lack of adequate causal explanations of the origin of novel morphologies and the evolution of developmental processes over geologic time. I argue that the first phase of the Developmental Synthesis is a partial explanatory reconciliation. More specifically, I contend that the rise of the developmental gene concept and the discovery of highly conserved developmental genes helped demonstrate the overlap in explanatory interests between the developmental sciences and other scientific fields within the domain of evolutionary biology. I argue this explanatory reconciliation led to the current second phase of the Developmental Synthesis, the integration of various biological fields. On my account, this multi- field integration includes developmental biology, embryology, epigenetics, genetics, morphology, and paleontology, all of which have a shared explanatory interest in the origin of novel morphologies and the evolution of developmental processes. Through analysis of the development of current evolutionary theory and recent empirical and theoretical work in evolutionary developmental biology (evo-devo), I argue the ongoing Developmental Synthesis promises to explain the origin of novel body structures and the evolution of diverse morphologies, explanations that are absent from current evolutionary theory but must be included in a comprehensive account of evolution. iii iv Acknowledgements First and foremost, this dissertation would not have been possible without the superb and irreplaceable guidance of my dissertation chair and friend, Rob Skipper. If all young philosophers had mentors like him, the profession would be better off. Likewise, this dissertation was substantially enhanced by the education and support I received from my other committee members, Dick Burian, Koffi Maglo, and Bob Richardson. They, along with Stuart Glennan and Tom Polger, did all they could to teach me the skills required to be a good philosopher. They pushed me when I needed to be pushed and continue to help me navigate our chosen profession. These philosophers have given me a truly excellent education. Special thanks to Mike Dietrich, who has on more than one occasion taken the time to discuss my research and suggest improvements. And thanks to John McEvoy for his comments as well. My family and friends must also be thanked, of course. My parents, Jim and Kim Craig, and my sister, Hayley, have supported me in countless ways. Their unending encouragement and personal investment in my success keeps me going. Like the others mentioned above, they have always had confidence in me, even when I had no confidence in myself. My oldest and dearest friend, Claire Hunter, has probably heard enough about the rigors of graduate school for her lifetime, for which I sincerely apologize. Her lasting friendship is invaluable to me and gives me hope. Finally, I must thank Nanny and Papaw. My education started with them. They got me started on this long road, and they never once let me down. Until his death in November 2009, Papaw always stood beside me, supported my decisions, and let me know I made him proud. He is sorely missed. Parts of this dissertation benefited from presentations at the 2009 ISHPSSB meeting in Brisbane, Australia, the 2009 Darwin’s Reach conference at Hofstra University, and the Department of Philosophy at the University of Cincinnati in 2010. The Charles Phelps Taft Dissertation Fellowship, the Department of Philosophy, and the University of Cincinnati have all graciously funded this work. Thanks to everyone who knew I could do this. There is no way to thank you enough. v Table of Contents Chapter 1: Scientific Change in Evolutionary Biology…………………………………………...1 1.1 Introduction……………………………………………………………………………1 1.2 The Modern Synthesis of the 1920s-1950s……………………………………………3 1.3 Motivation for the Developmental Synthesis…………………………………………5 1.4 Scientific Explanation and Relevance…………...……………………………………8 1.5 Reconciliation and Integration……………………………………………………….12 1.6 Predominant Areas of Research within Evo-Devo…………………………………..14 1.6.1 Comparative Embryology, Morphology, and Genomics…………………..15 1.6.2 Developmental Processes…………………………………………………..16 1.6.3 Theoretical and Computational Modeling…………………………………16 1.7 Dissertation Outline………………………………………………………………….18 1.8 Conclusion…………………………………………………………………………...20 Chapter 2: An Alternative Account of the Modern Synthesis…………………………………...22 2.1 Introduction…………………………………………………………………………..22 2.2 The Study of Evolution at the Turn of the 20th Century……………………………..23 2.3 Accounts of the Modern Synthesis…………………………...……………………...25 2.3.1 Provine on the Modern Synthesis………………………………………….27 2.3.2 Mayr on the Modern Synthesis…………………………………………….28 2.3.3 Amundson on the Modern Synthesis………………………………………30 2.4 Criticism of the Accounts…………………..………………………………………..31 2.5 Phase One: Reconciliation of Mendelism and Darwinism……………………...…...37 2.6 Phase Two: Multi-Field Integration………………………………………………….39 2.7 Conclusion…………………………………………………………………………...44 Chapter 3: The Insignificant Role of Development in the Modern Synthesis…………………...47 3.1 Introduction…………………………………………………………………………..47 3.2 The Predominant Account: Development and the Modern Synthesis……………….50 3.3 Developmentalist Explanations……………………………………………………...55 3.3.1 Descriptive Embryology…………………………………………………...53 3.3.2 Dissatisfaction with Descriptive Embryology……………………………..57 3.3.3 Experimental Embryology…………………………………………………59 3.3.4 Embryology of the 1920s…………………………………………………..64 3.3.5 Key Aspects of Developmentalist Explanations…………………………...67 vi 3.4 Explanatory Foundations of the Modern Synthesis………………………………….68 3.4.1 Fisher’s Genetical Theory of Natural Selection (GTNS)………………….69 3.4.2 Wright’s Shifting Balance Theory (SBT)………………………………….70 3.4.3 Key Aspects of Integrationist Explanations………………………………..72 3.5 Conclusion…………………………………………………………………………...73 Chapter 4: The Developmental Synthesis: Reconciliation and Multi-Field Integration……..…..75 4.1 Introduction…………………………………………………………………………..75 4.2 Phase One: Reconciliation of Explanatory Differences……………………………...76 4.2.1 The Developmental Gene Concept………………………….……………..77 4.2.2 The Discovery of Highly Conserved Developmental Genes………………82 4.2.3 The Reconciliation of the Developmental Synthesis in Summary………...87 4.3 Phase Two: Multi-Field Integration……………………………………………….....88 4.4 Conclusion……………………………………………………………………..…….94 Chapter 5: A Defense of Evo-Devo……………………………………………………………...96 5.1 Introduction…………………………………………………………………………..96 5.2 Carroll’s So-Called Revolution……………………………………………………....97 5.3 Evo-Devo: Claims and Criticisms………………………………………………….100 5.4 Conclusion………………………………………………………………………….106 Chapter 6: Extended Synthesis and Conceptual Difficulties for Population Genetics…………108 6.1 Introduction…………………………………………………………………………108 6.2 Pigliucci (2007) and Müller (2007): Extended Synthesis…………………………..110 6.3 Conceptual Difficulties……………………………………………………………..117 6.4 Conclusion………………………………………………………………………….122 References………………………………………………………………………………………125 vii Chapter 1 Scientific Change in Evolutionary Biology 1.1 Introduction This dissertation is a critical examination of the motivation for and structure of current scientific change in evolutionary biology. My primary focus is what I refer to as the Developmental Synthesis, an episode of change in evolutionary biology that spans the 20th and 21st centuries and has recently received considerable attention from biologists, philosophers, and historians. I defend the thesis that the Developmental Synthesis is a two-phase multi-field integration motivated by the lack of adequate causal explanations of the origin of novel morphological traits and the evolution of developmental processes. I argue that during the first phase of the Developmental Synthesis, the rise of the developmental gene concept and the discovery of highly conserved developmental genes reconciled substantive explanatory differences that separated the fields of developmental biology and embryology from the fields most active in the development of evolutionary theory during the first half of the 20th century. This explanatory
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