the structure of evolutionnary theory

STEPHEN JAY GOULD




The Structure Of
Evolutionary Theory

______________________________
THE BELKNAP PRESS OF
HARVARD UNIVERSITY PRESS
CAMBRIDGE,
MASSACHUSETTS
AND LONDON, ENGLAND



















Copyright © 2002 by the President and Fellows of Harvard College
All rights reserved
Printed in the United States of America

Library of Congress Cataloging-in-Publication Data

Gould, Stephen Jay.
The structure of evolutionary theory / Stephen Jay Gould.
p. cm.

Includes bibliographical references (p. )
ISBN 0-674-00613-5 (alk. paper)
1. Evolution (Biology) 2. Punctuated equilibrium (Evolution) I. Title.

QH366.2.G663 2002
576.8—dc21 2001043556

Sixth printing, 2002

__________________________________________
For Niles Eldredge and Elisabeth Vrba
May we always be the Three Musketeers
Prevailing with panache
From our manic and scrappy inception at Dijon
To our nonsatanic and happy reception at Doomsday
All For One and One For All

Contents

Chapter 1:
Defining and Revising the Structure of Evolutionary Theory 1

Part I, Chapters 2-7
The History of Darwinian Logic and Debate 91

Segue to Part II 585

Part II, Chapters 8-12
Towards a Revised and Expanded Evolutionary Theory 593

Bibliography 1344

Illustration Credits 1388

Index 1393

















vii

Expanded Contents

Chapter 1: Defining and Revising the Structure
of Evolutionary Theory 1

• Theories Need Both Essences and Histories 1

• The Structure of Evolutionary Theory: Revising the Three Central
Features of Darwinian Logic 12

• Apologia Pro Vita Sua 24
A Time to Keep 24
A Personal Odyssey 33

• Epitomes for a Long Development 48
Levels of Potential Originality 48
An Abstract of One Long Argument 53


Part I: The History of Darwinian Logic and Debate


Chapter 2: The Essence of Darwinism and the Basis of
Modern Orthodoxy: An Exegesis of the Origin of Species 93

• A Revolution in the Small 93

• Darwin as a Historical Methodologist 97
One Long Argument 97
The Problem of History 99
A Fourfold Continuum of Methods for the Inference of History 103

• Darwin as a Philosophical Revolutionary 116
The Causes of Nature's Harmony 116
Darwin and William Paley 116
Darwin and Adam Smith 121
The First Theme: The Organism as the Agent of Selection 125

ix




x Contents

The Second Theme: Natural Selection as a Creative Force 137
The Requirements for Variation 141
Copious 141
Small 143
Undirected 144
Gradualism 146
The Adaptationist Program 155
The Third Theme: The Uniformitarian Need to Extrapolate:
Environment as Enabler of Change 159

• Judgments of Importance 163
Chapter 3: Seeds of Hierarchy 170

• Lamarck and the Birth of Modern Evolutionism in
Two-Factor Theories 170
The Myths of Lamarck 170

Lamarck as a Source 174
Lamarck's Two-Factor Theory: Sources for the Two Parts 175
The First Set: Environment and Adaptation 176
The Second Set: Progress and Taxonomy 179
Distinctness of the Two Sets 181
Lamarck's Two-Factor Theory: The Hierarchy of
Progress and Deviation 175
Antinomies of the Two-Factor Theory 189

• An Interlude on Darwin's Reaction 192

• No Allmacht without Hierarchy: Weissman on Germinal Selection 197
The Allmacht of Selection 197
Weismann's Argument on Lamarck and the Allmacht of Selection 201
The Problem of Degeneration and Weismann's Impetus for
Germinal Selection 203
Some Antecedents to Hierarchy in German Evolutionary Thought 208
Haeckel's Descriptive Hierarchy in Levels of Organization 208
Roux's Theory of Intracorporeal Struggle 210
Germinal Selection as a Helpmate to Personal Selection 214
Germinal Selection as a Full Theory of Hierarchy 219

• Hints of Hierarchy in Supraorganismal Selection:
Darwin on the Principle of Divergence 224
Divergence and the Completion of Darwin's System 224
The Genesis of Divergence 232



Contents xi

Divergence as a Consequence of Natural Selection 234
The Failure of Darwin's Argument and the Need for
Species Selection 236
The Calculus of Individual Success 238
The Causes of Trends 240
Species Selection Based on Propensity for Extinction 246
Postscript: Solution to the Problem of the "Delicate Arrangement" 248

• Coda 249

Chapter 4: Internalism and Laws of Form:
Pre-Darwinian Alternatives to Functionalism 251

• Prologue: Darwin's Fateful Decision 251



• Two Ways to Glorify God in Nature 260
William Paley and British Functionalism: Praising God in the
Details of Design 262
Louis Agassiz and Continental Formalism: Praising God in the
Grandeur of Taxonomic Order 271
An Epilog on the Dichotomy 278

• Unity of Plan as the Strongest Version of Formalism:
The Pre-Darwinian Debate 281
Mehr Licht on Goethe's Leaf 281
Geoffroy and Cuvier 291
Cuvier and Conditions of Existence 291

Geoffroy's Formalist Vision 298
The Debate of 1830: Foreplay and Aftermath 304
Richard Owen and English Formalism:
The Archetype of Vertebrates 312
No Formalism Please, We're British 312
The Vertebrate Archetype: Constraint and Nonadaptation 316
Owen and Darwin 326

• Darwin's Strong but Limited Interest in Structural Constraint 330
Darwin's Debt to Both Poles of the Dichotomy 330
Darwin on Correlation of Parts 332
The "Quite Subordinate Position" of Constraint to Selection 339

Chapter 5: The Fruitful Facets of Galton's Polyhedron:
Channels and Saltations in Post-Darwinian Formalism 342

• Galton's Polyhedron 342


xii Contents

• Orthogenesis as a Theory of Channels and One-Way Streets:
the Marginalization of Darwinism 351
Misconceptions and Relative Frequencies 351
Theodor Eimer and the Ohnmacht of Selection 355
Alpheus Hyatt: An Orthogenetic Hard Line from the
World of Mollusks 365
CO. Whitman: An Orthogenetic Dove in Darwin's
World of Pigeons 383

• Saltation as a Theory of Internal Impetus: A Second Formalist Strategy
for Pushing Darwinism to a Causal Periphery 396
William Bateson: The Documentation of Inherent Discontinuity 396
Hugo de Vries: A Most Reluctant Non-Darwinian 415
Dousing the Great Party of 1909 415
The (Not So Contradictory) Sources of the Mutation Theory 418
The Mutation Theory: Origin and Central Tenets 425
Darwinism and the Mutation Theory 439
Confusing Rhetoric and the Personal Factor 439
The Logic of Darwinism and Its Different Place in
de Vries' System 443
De Vries on Macroevolution 446
Richard Goldschmidt's Appropriate Role as a Formalist
Embodiment of All that Pure Darwinism Must Oppose 451

Chapter 6: Pattern and Progress on the Geological Stage 467

• Darwin and the Fruits of Biotic Competition 467
A Geological License for Progress 467
The Predominance of Biotic Competition and Its Sequelae 470

• Uniformity on the Geological Stage 479
Lyell's Victory in Fact and Rhetoric 479
Catastrophism as Good Science: Cuvier's Essay 484
Darwin's Geological Need and Kelvin's Odious Spectre 492
A Question of Time (Too Little Geology) 496
A Question of Direction (Too Much Geology) 497

Chapter 7: The Modern Synthesis as a Limited Consensus 503

• Why Synthesis? 503

• Synthesis as Restriction 505
The Initial Goal of Rejecting Old Alternatives 505



Contents xiii

R. A. Fisher and the Darwinian Core 508
J. B. S. Haldane and the Initial Pluralism of the Synthesis 514
J. S. Huxley: Pluralism of the Type 516

• Synthesis as Hardening 518
The Later Goal of Exalting Selection's Power 518
Increasing Emphasis on Selection and Adaptation between the
First (1937) and Last (1951) Edition of Dobzhansky's Genetics
and the Origin of Species 524
The Shift in G. G. Simpson's Explanation of "Quantum Evolution"
from Drift and Nonadaptation (1944) to the Embodiment of Strict
Adaptation (1953) 528
Mayr at the Inception (1942) and Codification (1963): Shifting
from the "Genetic Consistency" to the "Adaptationist" Paradigm 531
Why Hardening? 541

• Hardening on the Other Two Legs of the Darwinian Tripod 543
Levels of Selection 544
Extrapolation into Geological Time 556

• From Overstressed Doubt to Overextended Certainty 566

A Tale of Two Centennials 566
All Quiet on the Textbook Front 576
Adaptation and Natural Selection 577
Reduction and Trivialization of Macroevolution 579

Segue to Part II 585

Part II: Towards a Revised and Expanded
Evolutionary Theory

Chapter 8: Species as Individuals in the Hierarchical
Theory of Selection 595

• The Evolutionary Definition of Individuality 595
An Individualistic Prolegomenon 595
The Meaning of Individuality and the Expansion of the Darwinian
Research Program 597
Criteria for Vernacular Individuality 602
Criteria for Evolutionary Individuality 608
• The Evolutionary Definition of Selective Agency and the Fallacy of
Selfish Genes 613


xiv Contents

A Fruitful Error of Logic 613
Hierarchical vs. Genie Selectionism 614
The Distinction of Replicators and Interactors as a
Framework for Discussion 615
Faithful Replication as the Central Criterion for the Gene-

Centered View of Evolution 616
Sieves, Plurifiers, and the Nature of Selection: The Rejection of
Replication as a Criterion of Agency 619
Interaction as the Proper Criterion for Identifying
Units of Selection 622
The Internal Incoherence of Gene Selectionism 625
Bookkeeping and Causality: The Fundamental Error of
Gene Selectionism 632
Gambits of Reform and Retreat by Gene Selectionists 637

• Logical and Empirical Foundations for the Theory of
Hierarchical Selection 644
Logical Validation and Empirical Challenges 644
R. A. Fisher and the Compelling Logic of Species Selection 644
The Classical Arguments against Efficacy of
Higher-Level Selection 646
Overcoming These Classical Arguments, in Practice for
Interdemic Selection, but in Principle for Species Selection 648
Emergence and the Proper Criterion for Species Selection 652
Differential Proliferation or Downward Effect? 652
Shall Emergent Characters or Emergent Fitnesses Define the
Operation of Species Selection? 656
Hierarchy and the Sixfold Way 673
A Literary Prologue for the Two Major Properties
of Hierarchies 673
Redressing the Tyranny of the Organism: Comments on
Characteristic Features and Differences among Six
Primary Levels 681
The Gene-Individual 683
Motoo Kimura and the "Neutral Theory of Molecular Evolution" 684

True Genie Selection 689
The Cell-Individual 695
The Organism-Individual 700
The Deme-Individual 701
The Species-Individual 703




Contents xv

Species as Individuals 703
Species as Interactors 704
Species Selection as Potent 709
The Clade-Individual 712

• The Grand Analogy: A Speciational Basis for Macroevolution 714
Presentation of the Chart for Macroevolutionary Distinctiveness 714
The Particulars of Macroevolutionary Explanation 716
The Structural Basis 716
Criteria for Individuality 720
Contrasting Modalities of Change: The Basic Categories 721
Ontogenetic Drive: The Analogy of Lamarckism
and Anagenesis 722
Reproductive Drive: Directional Speciation as an Important
and Irreducible Macroevolutionary Mode Separate from
Species Selection 724
Species Selection, Wright's Rule, and the Power of Interaction
with Directional Speciation 731
Species Level Drifts as More Powerful than the Analogous

Phenomena in Microevolution 735
The Scaling of External and Internal Environments 738
Summary Comments on the Strengths of Species Selection
and its Interaction with Other Macroevolutionary Causes
of Change 741

Chapter 9: Punctuated Equilibrium and the Validation of
Macroevolutionary Theory 745

• What Every Paleontologist Knows 745
An Introductory Example 745
Testimonials to Common Knowledge 749
Darwinian Solutions and Paradoxes 755
The Paradox of Insulation from Disproof 758
The Paradox of Stymied Practice 761

• The Primary Claims of Punctuated Equilibrium 765
Data and Definitions 765
Microevolutionary Links 774
Macroevolutionary Implications 781
Tempo and the Significance of Stasis 782
Mode and the Speciational Foundation of Macroevolution 783



xvi Contents

• The Scientific Debate on Punctuated Equilibrium: Critiques
and Responses 784
Critiques Based on the Definability of Paleontological Species 784

Empirical Affirmation 784
Reasons for a Potential Systematic Underestimation of Biospecies
by Paleospecies 789
Reasons for a Potential Systematic Overestimation of Biospecies
by Paleospecies 792
Reasons Why an Observed Punctuational Pattern Might Not
Represent Speciation 793
Critiques Based on Denying Events of Speciation as the Primary
Locus of Change 796
Critiques Based on Supposed Failures of Empirical Results to
Affirm Predictions of Punctuated Equilibrium 802
Claims for Empirical Refutation by Cases 802
Phenotypes 802
Genotypes 810
Empirical Tests of Conformity with Models 812

• Sources of Data for Testing Punctuated Equilibrium 822
Preamble 822
The Equilibrium in Punctuated Equilibrium: Quantitatively
Documented Patterns of Stasis in Unbranched Segments
of Lineages 824
The Punctuations of Punctuated Equilibrium: Tempo and
Mode in the Origin of Paleospecies 839
The Inference of Cladogenesis by the Criterion of
Ancestral Survival 840
The "Dissection" of Punctuations to Infer Both Existence
and Modality 850
Time 851
Geography 852
Morphometric Mode 852

Proper and Adequate Tests of Relative Frequencies: The Strong
Empirical Validation of Punctuated Equilibrium 854
The Indispensability of Data on Relative Frequencies 854
Relative Frequencies for Higher Taxa in Entire Biotas 856
Relative Frequencies for Entire Clades 866
Causal Clues from Differential Patterns of
Relative Frequencies 870




Contents xvii

• The Broader Implications of Punctuated Equilibrium for
Evolutionary Theory and General Notions of Change 874
What Changes May Punctuated Equilibrium Instigate in Our
Views about Evolutionary Mechanisms and the History of Life? 874
The Explanation and Broader Meaning of Stasis 874
Frequency 875
Generality 876
Causality 877
Punctuation, the Origin of New Macroevolutionary Individuals,
and Resulting Implications for Evolutionary Theory 885
Trends 886
The Speciational Reformulation of Macroevolution 893
Life Itself 897
General Rules 901
Particular Cases 905
Horses as the Exemplar of "Life's Little Joke" 905
Rethinking Human Evolution 908

Ecological and Higher-Level Extensions 916
Punctuation All the Way Up and Down? The Generalization and
Broader Utility of Punctuated Equilibrium (in More Than a
Metaphorical Sense) at Other Levels of Evolution, and for Other
Disciplines In and Outside the Natural Sciences 922
General Models for Punctuated Equilibrium 922
Punctuational Change at Other Levels and Scales of Evolution 928
A Preliminary Note on Homology and Analogy in the
Conceptual Realm 928
Punctuation Below the Species Level 931
Punctuation Above the Species Level 936
Stasis Analogs: Trending and Non-Trending in the Geological
History of Clades 936
Punctuational Analogs in Lineages: The Pace of
Morphological Innovation 939
Punctuational Analogs in Faunas and Ecosystems 946
Punctuational Models in Other Disciplines: Towards a
General Theory of Change 952
Principles for a Choice of Examples 952
Examples from the History of Human Artifacts and Cultures 952
Examples from Human Institutions and Theories about the
Natural World 957






xviii Contents

Two Concluding Examples, a General Statement, and a Coda 962

• Appendix: A Largely Sociological (and Fully Partisan) History of
the Impact and Critique of Punctuated Equilibrium 972
The Entrance of Punctuated Equilibrium into Common Language
and General Culture 972
An Episodic History of Punctuated Equilibrium 979
Early Stages and Future Contexts 979
Creationist Misappropriation of Punctuated Equilibrium 986
Punctuated Equilibrium in Journalism and Textbooks 990
The Personal Aspect of Professional Reaction 999
The Case Ad Hominem against Punctuated Equilibrium 1000
An Interlude on Sources of Error 1010
The Wages of Jealousy 1014
The Descent to Nastiness 1014
The Most Unkindest Cut of All 1019
The Wisdom of Agassiz's and von Baer's Threefold History of
Scientific Ideas 1021
A Coda on the Kindness and Generosity of Most Colleagues 1022

Chapter 10: The Integration of Constraint and Adaptation (Structure
and Function) in Ontogeny and Phylogeny: Historical Constraints
and the Evolution of Development 1025

• Constraint as a Positive Concept 1025
Two Kinds of Positivity 1025
An Etymological Introduction 1025
The First (Empirical) Positive Meaning of Channeling 1027
The Second (Definitional) Positive Meaning of Causes outside
Accepted Mechanisms 1032

Heterochrony and Allometry as the Locus Classicus of the First
Positive (Empirical) Meaning. Channeled Directionality by
Constraint. 1037
The Two Structural Themes of Internally Set Channels and Ease
of Transformation as Potentially Synergistic with Functional
Causality by Natural Selection: Increasing Shell Stability in the
Gryphaea Heterochronocline 1040
Ontogenetically Channeled Allometric Constraint as a Primary
Basis of Expressed Evolutionary Variation: The Full Geographic
and Morphological Range of Cerion uva 1045




Contents xix

The Aptive Triangle and the Second Positive Meaning: Constraint
as a Theory-Bound Term for Patterns and Directions Not Built
Exclusively (Or Sometimes Even at All) by Natural Selection 1051
The Model of the Aptive Triangle 1051
Distinguishing and Sharpening the Two Great Questions 1053
The Structural Vertex 1053
The Historical Vertex 1055
An Epitome for the Theory-Bound Nature of Constraint
Terminology 1057

• Deep Homology and Pervasive Parallelism: Historical Constraint
as the Primary Gatekeeper and Guardian of Morphospace 1061
A Historical and Conceptual Analysis of the Underappreciated
Importance of Parallelism for Evolutionary Theory 1061

A Context for Excitement 1061
A Terminological Excursus on the Meaning of Parallelism 1069
The Nine Fateful Little Words of E. Ray Lankester 1069
The Terminological Origin and Debate about the Meaning
and Utility of Parallelism 1076
A Symphony in Four Movements on the Role of Historical Constraint
in Evolution: Towards the Harmonious Rebalancing of Form and
Function in Evolutionary Theory 1089
Movement One, Statement: Deep Homology across Phyla: Mayr's
Functional Certainty and Geoffroy's Structural Vindication 1089
Deep Homology, Archetypal Theories, and
Historical Constraint 1089
Mehr Licht (More Light) on Goethe's Angiosperm Archetype 1092
Hoxology and Geoffroy's First Archetypal Theory of
Segmental Homology 1095
An Epitome and Capsule History of Hoxology 1095
Vertebrate Homologs in Structure and Action 1101
Segmental Homologies of Arthropods and Vertebrates:
Geoffroy's Vindication 1106
Rediscovering the Vertebrate Rhombomeres 1107
More Extensive Homologies throughout the
Developing Somites 1109
Some Caveats and Tentative Conclusions 1112
Geoffrey's Second Archetypal Theory of Dorso-Ventral
Inversion in the Common Bilaterian Groundplan 1117

xx Contents

Movement Two, Elaboration: Parallelism of Underlying
Generators: Deep Homology Builds Positive Channels of
Constraint 1122
Parallelism All the Way Down: Shining a Light and
Feeding the Walk 1122
Parallelism in the Large: Pax-6 and the Homology of Developmental
Pathways in Homoplastic Eyes of Several Phyla 1123
Data and Discovery 1123
Theoretical Issues 1127
A Question of Priority 1130
Parallelism in the Small: The Origin of Crustacean Feeding
Organs 1132
Pharaonic Bricks and Corinthian Columns 1134
Movement Three, Scherzo: Does Evolutionary Change Often
Proceed by Saltation Down Channels of Historical
Constraint? 1142
Movement Four, Recapitulation and Summary: Early Establishment
of Rules and the Inhomogenous Population of Morphospace:
Dobzhansky's Landscape as Primarily Structural and Historical,
Not Functional and Immediate 1147
Bilaterian History as Top-Down by Tinkering of an Initial Set
of Rules, Not Bottom-Up by Adding Increments of Complexity 1147
Setting of Historical Constraints in the Cambrian Explosion 1155
Channeling the Subsequent Directions of Bilaterian History
from the Inside 1161
An Epilog on Dobzhansky's Landscape and the Dominant Role
of Historical Constraint in the Clumped Population of

Morphospace 1173

Chapter 11: The Integration of Constraint and Adaptation (Structure
and Function) in Ontogeny and Phylogeny: Structural Constraints,
Spandrels, and the Centrality of Exaptation in Macroevolution 1179

• The Timeless Physics of Evolved Function 1179
Structuralism's Odd Man Outside 1179
D'Arcy Thompson's Science of Form 1182
The Structure of an Argument 1182
The Tactic and Application of an Argument 1189
The Admitted Limitation and Ultimate Failure of
an Argument 1196





Contents xxi

Odd Man In (D'Arcy Thompson's Structuralist Critique of
Darwinism) and Odd Man Out (His Disparagement
of Historicism) 1200
An Epilog to an Argument 1207
Order for Free and Realms of Relevance for
Thompsonian Structuralism 1208

• Exapting the Rich and Inevitable Spandrels of History 1214
Nietzsche's Most Important Proposition of Historical Method 1214
Exaptation and the Principle of Quirky Functional Shift: The Restricted

Darwinian Version as the Ground of Contingency 1218
How Darwin Resolved Mivart's Challenge of Incipient Stages 1218
The Two Great Historical and Structural Implications of
Quirky Functional Shift 1224
How Exaptation Completes and Rationalizes the Terminology of
Evolutionary Change by Functional Shifting 1229
Key Criteria and Examples of Exaptation 1234
The Complete Version, Replete with Spandrels: Exaptation and the
Terminology of Nonadaptative Origin 1246
The More Radical Category of Exapted Features with Truly
Nonadaptive Origins as Structural Constraints 1246
Defining and Defending Spandrels: A Revisit to San Marco 1249
Three Major Reasons for the Centrality of Spandrels, and
Therefore of Nonadaptation, in Evolutionary Theory 1258

• The Exaptive Pool: The Proper Conceptual Formula and Ground
of Evolvability 1270
Resolving the Paradox of Evolvability and Defining the
Exaptive Pool 1270
The Taxonomy of the Exaptive Pool 1277
Franklins and Miltons, or Inherent Potentials vs.
Available Things 1277
Choosing a Fundamentum Divisionis for a Taxonomy:
An Apparently Arcane and Linguistic Matter That Actually
Embodies a Central Scientific Decision 1280
Cross-Level Effects as Miltonic Spandrels, Not Franklinian
Potentials: The Nub of Integration and Radical Importance 1286
A Closing Comment to Resolve the Macroevolutionary Paradox
that Constraint Ensures Flexibility Whereas Selection Crafts
Restriction 1294

xxii Contents

Chapter 12: Tiers of Time and Trials of Extrapolationism,
With an Epilog on the Interaction of General Theory and
Contingent History 1296

• Failure of Extrapolationism in the Non-Isotropy of Time
and Geology 1296
The Specter of Catastrophic Mass Extinction: Darwin
to Chicxulub 1296
The Paradox of the First Tier: Towards a General Theory of
Tiers of Time 1320

• An Epilog on Theory and History in Creating the Grandeur of
This View of Life 1332

CHAPTER ONE



Defining and Revising
the Structure of Evolutionary Theory

Theories Need Both Essences and Histories

In a famous passage added to later editions of the Origin of Species, Charles
Darwin (1872, p. 134) generalized his opening statement on the apparent absurdity
of evolving a complex eye through a long series of gradual steps by reminding his
readers that they should always treat "obvious" truths with skepticism. In so doing,
Darwin also challenged the celebrated definition of science as "organized common
sense," as championed by his dear friend Thomas Henry Huxley. Darwin wrote:
"When it was first said that the sun stood still and world turned round, the common
sense of mankind declared the doctrine false; but the old saying of Vox populi, vox
Dei [the voice of the people is the voice of God], as every philosopher knows,
cannot be trusted in science."
Despite his firm residence within England's higher social classes, Darwin took
a fully egalitarian approach towards sources of expertise, knowing full well that the
most dependable data on behavior and breeding of domesticated and cultivated
organisms would be obtained from active farmers and husbandmen, not from lords
of their manors or authors of theoretical treatises. As Ghiselin (1969) so cogently
stated, Darwin maintained an uncompromisingly "aristocratic" set of values
towards judgment of his work—that is, he cared not a whit for the outpourings of
vox populi, but fretted endlessly and fearfully about the opinions of a very few key
people blessed with the rare mix of intelligence, zeal, and attentive practice that we
call expertise (a democratic human property, respecting only the requisite mental
skills and emotional toughness, and bearing no intrinsic correlation to class,
profession or any other fortuity of social circumstance).
Darwin ranked Hugh Falconer, the Scottish surgeon, paleontologist, and
Indian tea grower, within this most discriminating of all his social groups, a panel
that included Hooker, Huxley and Lyell as the most prominent members. Thus,
when Falconer wrote his important 1863 paper on American fossil elephants (see
Chapter 9, pages 745-749, for full discussion of this incident), Darwin flooded
himself with anticipatory fear, but then rejoiced in his critic's generally favorable

reception of evolution, as embodied in the closing
1




2 THE STRUCTURE OF EVOLUTIONARY THEORY

sentence of Falconer's key section: "Darwin has, beyond all his cotemporaries
[sic], given an impulse to the philosophical investigation of the most backward and
obscure branch of the Biological Sciences of his day; he has laid the foundations of
a great edifice; but he need not be surprised if, in the progress of erection, the
superstructure is altered by his successors, like the Duomo of Milan, from the
roman to a different style of architecture."
In a letter to Falconer on October 1, 1862 (in F. Darwin, 1903, volume 1, p.
206), Darwin explicitly addressed this passage in Falconer's text. (Darwin had
received an advance copy of the manuscript, along with Falconer's request for
review and criticism—hence Darwin's reply, in 1862, to a text not printed until the
following year): "To return to your concluding sentence: far from being surprised,
I look at it as absolutely certain that very much in the Origin will be proved
rubbish; but I expect and hope that the framework will stand."
The statement that God (or the Devil, in some versions) dwells in the details
must rank among the most widely cited intellectual witticisms of our time. As with
many clever epigrams that spark the reaction “I wish I'd said that!”, attribution of
authorship tends to drift towards appropriate famous sources. (Virtually any nifty
evolutionary saying eventually migrates to Т. Н. Huxley, just as vernacular
commentary about modern America moves towards Mr. Berra.) The apostle of
modernism in architecture, Ludwig Mies van der Rohe, may, or may not, have said
that "God dwells in the details," but the plethora of tiny and subtle choices that
distinguish the elegance of his great buildings from the utter drabness of

superficially similar glass boxes throughout the world surely validates his
candidacy for an optimal linkage of word and deed.
Architecture may assert a more concrete claim, but nothing beats the
extraordinary subtlety of language as a medium for expressing the importance of
apparently trivial details. The architectural metaphors of Milan's cathedral, used by
both Falconer and Darwin, may strike us as effectively identical at first read.
Falconer says that the foundations will persist as Darwin's legacy, but that the
superstructure will probably be reconstructed in a quite different style. Darwin
responds by acknowledging Falconer's conjecture that the theory of natural
selection will undergo substantial change; indeed, in his characteristically diffident
way, Darwin even professes himself "absolutely certain" that much of the Origin's
content will be exposed as "rubbish." But he then states not only a hope, but also
an expectation, that the "framework" will stand.
We might easily read this correspondence too casually as a polite dialogue
between friends, airing a few unimportant disagreements amidst a commitment to
mutual support. But I think that this exchange between Falconer and Darwin
includes a far more "edgy" quality beneath its diplomacy. Consider the different
predictions that flow from the disparate metaphors chosen by each author for the
Duomo of Milan—Falconer's "foundation" vs. Darwin's "framework." After all, a
foundation is an invisible system of support, sunk into the ground, and intended as
protection against sinking or toppling of the


Defining and Revising the Structure of Evolutionary Theory 3

overlying public structure. A framework, on the other hand, defines the basic form
and outline of the public structure itself. Thus, the two men conjure up very
different pictures in their crystal balls. Falconer expects that the underlying
evolutionary principle of descent with modification will persist as a factual
foundation for forthcoming theories devised to explain the genealogical tree of life.

Darwin counters that the theory of natural selection will persist as a basic
explanation of evolution, -even though many details, and even some subsidiary
generalities, cited within the Origin will later be rejected as false, or even illogical.
I stress this distinction, so verbally and disarmingly trivial at a first and
superficial skim through Falconer's and Darwin's words, but so incisive and
portentous as contrasting predictions about the history of evolutionary theory,
because my own position—closer to Falconer than to Darwin, but in accord with
Darwin on one key point—led me to write this book, while also supplying the
organizing principle for the "one long argument" of its entirety. I do believe that
the Darwinian framework, and not just the foundation, persists in the emerging
structure of a more adequate evolutionary theory. But I also hold, with Falconer,
that substantial changes, introduced during the last half of the 20th century, have
built a structure so expanded beyond the original Darwinian core, and so enlarged
by new principles of macroevolutionary explanation, that the full exposition, while
remaining within the domain of Darwinian logic, must be construed as basically
different from the canonical theory of natural selection, rather than simply
extended.
A closer study of the material basis for Falconer and Darwin's metaphors—
the Duomo (or Cathedral) of Milan—might help to clarify this important
distinction. As with so many buildings of such size, expense, and centrality (both
geographically and spiritually), the construction of the Duomo occupied several
centuries and included an amalgam of radically changing styles and purposes.
Construction began at the chevet, or eastern end, of the cathedral in the late 14th
century. The tall windows of the chevet, with their glorious flamboyant tracery,
strike me as the finest achievement of the entire structure, and as the greatest
artistic expression of this highly ornamented latest Gothic style. (The term
"flamboyant" literally refers to the flame-shaped element so extensively used in the
tracery, but the word then came to mean "richly decorated" and "showy," initially
as an apt description of the overall style, but then extended to the more general
meaning used today.)

Coming now to the main point, construction then slowed considerably, and
the main western facade and entrance way (Fig. 1-1) dates from the late 16th
century, when stylistic preferences had changed drastically from the points, curves
and traceries of Gothic to the orthogonal, low-angled or gently rounded lintels and
pediments of classical Baroque preferences. Thus, the first two tiers of the main
(western) entrance to the Duomo display a style that, in one sense, could not be
more formally discordant with Gothic elements of design, but that somehow
became integrated into an interesting coherence. (The third tier of the western
facade, built much later, returned to a "retro" Gothic style, thus suggesting a
metaphorical reversal of phylogenetic conventions, as
4 THE STRUCTURE OF EVOLUTIONARY THEORY



1-1. The west facade (main entrance) of Milan Cathedral, built in baroque style in the 16th
century, with a retro-gothic third tier added later.


up leads to older—in style if not in actual time of emplacement!) Finally, in a
distinctive and controversial icing upon the entire structure (Fig. 1-2), the
"wedding cake," or row-upon-row of Gothic pinnacles festooning the tops of all
walls and arches with their purely ornamental forms, did not crown the edifice
until the beginning of the 19th century, when Napoleon conquered the city and
ordered their construction to complete the Duomo after so many centuries of work.
(These pinnacle forests may amuse or disgust architectural purists, but no one can
deny their unintended role in making the Duomo so uniquely and immediately
recognizable as the icon of the city.)
How, then, shall we state the most appropriate contrast between the Duomo of
Milan and the building of evolutionary theory since Darwin's Origin in 1859? If
we grant continuity to the intellectual edifice (as implied by

Defining and Revising the Structure of Evolutionary Theory 5

comparison with a discrete building that continually grew but did not change its
location or basic function), then how shall we conceive "the structure of
evolutionary theory" (chosen, in large measure, as the title for this book because I
wanted to address, at least in practical terms, this central question in the history
and content of science)? Shall we accept Darwin's triumphalist stance and hold that
the framework remains basically fixed, with all visually substantial change
analogous to the non-structural, and literally superficial, icing of topmost
pinnacles? Or shall we embrace Falconer's richer and more critical, but still fully
positive, concept of a structure that has changed in radi-



1-2. The "wedding cake" pinnacles that festoon the top of Milan Cathedral, and that were
not built until the first years of the 19th century after Napoleon
conquered the city.


6 THE STRUCTURE OF EVOLUTIONARY THEORY

cal ways by incorporating entirely different styles into crucial parts of the building
(even the front entrance!), while still managing to integrate all the differences into
a coherent and functional whole, encompassing more and more territory in its
continuing enlargement?
Darwin's version remains Gothic, and basically unchanged beyond the visual
equivalent of lip service. Falconer's version retains the Gothic base as a positive
constraint and director, but then branches out into novel forms that mesh with the

base but convert the growing structure into a new entity, largely defined by the
outlines of its history. (Note that no one has suggested the third alternative, often
the fate of cathedrals—destruction, either total or, partial, followed by a new
building of contrary or oppositional form, erected over a different foundation.)
In order to enter such a discourse about "the structure of evolutionary theory"
at all, we must accept the validity, or at least the intellectual coherence and
potential definability, of some key postulates and assumptions that are often not
spelled out at all (especially by scientists supposedly engaged in the work), and
are, moreover, not always granted this form of intelligibility by philosophers and
social critics who do engage such questions explicitly. Most importantly, I must be
able to describe a construct like "evolutionary theory" as a genuine "thing"—an
entity with discrete boundaries and a definable history—especially if I want to
"cash out," as more than a confusingly poetic image, an analogy to the indubitable
bricks and mortar of a cathedral.
In particular, and to formulate the general problem in terms of the specific
example needed to justify the existence of this book, can "Darwinism" or
"Darwinian theory" be treated as an entity with defining properties of "anatomical
form" that permit us to specify a beginning and, most crucially for the analysis I
wish to pursue, to judge the subsequent history of Darwinism with enough rigor to
evaluate successes, failures and, especially, the degree and character of alterations?
This book asserts, as its key premise and one long argument, that such an
understanding of modern evolutionary theory places the subject in a particularly
"happy" intellectual status—with the central core of Darwinian logic sufficiently
intact to maintain continuity as the centerpiece of the entire field, but with enough
important changes (to all major branches extending from this core) to alter the
structure of evolutionary theory into something truly different by expansion,
addition, and redefinition. In short, "The structure of evolutionary theory"
combines enough stability for coherence with enough change to keep any keen
mind in a perpetual mode of search and challenge.
The distinction between Falconer's and Darwin's predictions, a key ingredient

in my analysis, rests upon our ability to define the central features of Darwinism
(its autapomorphies, if you will), so that we may then discern whether the extent of
alteration in our modern understanding of evolutionary mechanisms and causes
remains within the central logic of this Darwinian foundation, or has now changed
so profoundly that, by any fair criterion in vernacular understanding of language,
or by any more formal account of departure from original premises, our current
explanatory theory must be de-

Defining and Revising the Structure of Evolutionary Theory 7

scribed as a different kind of mental "thing." How, in short, can such an intellectual
entity be defined? And what degree of change can be tolerated or accommodated
within the structure of such an entity before we must alter the name and declare the
entity invalid or overthrown? Or do such questions just represent a fool's errand
from the start, because intellectual positions can't be reified into sufficient
equivalents of buildings or organisms to bear the weight of such an inquiry?
As arrogant as I may be in general, I am not sufficiently doltish or
vainglorious to imagine that I can meaningfully address the deep philosophical
questions embedded within this general inquiry of our intellectual ages—that is,
fruitful modes of analysis for the history of human thought. I shall therefore take
refuge in an escape route that has traditionally been granted to scientists: the liberty
to act as a practical philistine. Instead of suggesting a principled and general
solution, I shall ask whether I can specify an operational way to define
"Darwinism" (and other intellectual entities) in a manner specific enough to win
shared agreement and understanding among readers, but broad enough to avoid the
doctrinal quarrels about membership and allegiance that always seem to arise when
we define intellectual commitments as pledges of fealty to lists of dogmata (not to
mention initiation rites, secret handshakes and membership cards—in short, the
intellectual paraphernalia that led Karl Marx to make his famous comment to a
French journalist: "je ne suis pas marxiste").

As a working proposal, and as so often in this book (and in human affairs in
general), a "Goldilocks solution" embodies the blessedly practical kind of approach
that permits contentious and self-serving human beings (God love us) to break
intellectual bread together in pursuit of common goals rather than personal
triumph. (For this reason, I have always preferred, as guides to human action,
messy hypothetical imperatives like the Golden Rule, based on negotiation,
compromise and general respect, to the Kantian categorical imperatives of absolute
righteousness, in whose name we so often murder and maim until we decide that
we had followed the wrong instantiation of the right generality.) We must, in short
and in this case, steer between the "too little" of refusing to grant any kind of
"essence," or hard anatomy of defining concepts, to a theory like Darwinism; and
the "too much" of an identification so burdened with a long checklist of exigent
criteria that we will either spend all our time debating the status of particular items
(and never addressing the heart or central meaning of the theory), or we will waste
our efforts, and poison our communities, with arguments about credentials and
anathemata, applied to individual applicants for membership.
In his brilliant attempt to write a "living" history and philosophy of science
about the contemporary restructuring of taxonomic theory by phenetic and cladistic
approaches, Hull (1988) presents the most cogent argument I have ever read for
"too little" on Goldilocks's continuum, as embodied in his defense of theories as
"conceptual lineages" (1988, pp. 15-18). I enthusiastically support Hull's decision
to treat theories as "things," or individuals in the crucial sense of coherent
historical entities—and in opposition to the stan-