The Structure of Evolutionary Theory Page 11

  AN ABSTRACT OF ONE LONG ARGUMENT

  I have insisted, borrowing Darwin's famous line in my arrogance, that this “whole volume is one long argument,” flowing logically and sequentially from a clear beginning in Darwin's Origin to our current reformulations of evolutionary theory. But this structural thread of Ariadne can easily become lost in the labyrinth of my tendencies to expatiate on little factual gems, or to follow the thoughts of leading scientists into small, if lovely, byways of their mental complexities. Hence, I need to present summaries and epitomes as guidelines.

  Long books, like large bureaucracies, can easily get bogged down in a ba­roque layering of summary within summary. The United States House of Representatives has a Committee on Committees (I kid you not), undoubt­edly embellished with subcommittees thereof. And we must not forget Jona­than Swift's famous verse on the fractality of growing triviality in scholarly commentary:

  So, naturalists observe, a flea

  Hath smaller fleas that on him prey;

  And these have smaller still to bite 'em

  And so proceed ad infinitum.

  Thus every poet, in his kind,

  Is bit by him that comes behind.

  I wrote, on page 13, that this book includes three levels of embedding for this long argument — the summary in this chapter, the epitome of Darwin in [Page 54] Chapter 2, and the development of the totality. Now, and most sheepishly, I add two more, for a fractal total of five — the listed abstract, in pure “book order,” of this section, and (God help us) the epitome of this epitome, pre­sented now to introduce and guide the list.

  I develop my argument throughout this book by asserting, first, that the central logic of Darwinism can be depicted as a branching tree with three ma­jor limbs devoted to selection's agency, efficacy and scope. Second, that Dar­win, despite his heroic and explicit efforts, could not fully “cash out” his the­ory in terms of the stated commitments on each branch — and that he had to allow crucial exceptions, or at least express substantial fears, in each domain (admitting species selection to resolve the problem of diversity; permitting an uncomfortably large role for formalist correlations of growth as compromis­ers of strict adaptationism; expressing worry that mass extinction, if more than an artifact of an imperfect fossil record, would derail the extrapolationist premise of his system). Third, that the subsequent history of evolution­ary debate has focused so strongly upon the key claims of these three essential branches that we may use engagement with them as a primary criterion for distinguishing the central from the secondary when we need to gauge the im­portance of challenges to the Darwinian consensus. Fourth, that we should not be surprised by the prominence of these three themes, for they embody (in their biological specificity) the broadest underlying issues in scientific expla­nation, and in the nature of change and history: levels of structure and causal­ity, rates of alteration, directions of causal flow, the possibility of causal uni­fication by reduction to the lowest level vs. autonomy and interaction of irreducible levels, punctuational vs. gradual change, causal and temporal tier­ing vs. smooth extrapolation. Fifth, that the most interesting and impor­tant debates in our contemporary science continue to engage the same three themes, thus requiring the vista of history to appreciate the continuity and logical ordering that extends right back to Darwinian beginnings. Sixth, that our best modern understanding of the structure of evolutionary theory has re­versed the harmful dichotomization of earlier debates (Darwinian fealty vs. destructive attempts to trivialize or overturn the mechanism of selection) by confronting the same inadequacies of strict Darwinism, but this time intro­ducing important additions and revised formulations that preserve the Dar­winian foundation, but build a theory of substantial expansion and novelty upon a retained selectionist core.

  This logic and development may be defended as tolerably impersonal and universal, but any book of this length and complexity, and of so idiosyncratic a style and structure, must also own its authorial singularities. The Structure of Evolutionary Theory emerges, first of all, from my professional focus as a paleontologist and a student of macroevolution, defined, as explained on page 38, as descriptive phenomenology prior to any decision about the need for distinctive theory (my view) or the possibility of full subsumption un­der microevolutionary principles (the view of Darwin and the Modern Syn­thesis). The contingency of history guarantees that any body of theory will underdetermine important details, and even general flows, in the realized [Page 55] pageant of life's phylogeny on Earth — and such a claim for nontheoretical independence of macroevolution generates no dispute, even between rigid reductionists who grant no separate theoretical space to macroevolution, and biologists, like myself, who envisage an important role for distinctive macroevolutionary theory within an expanded and reformulated Darwinian view of life.

  In his description of the reductionist view of classical Darwinism — his own opinion in positive support, not a simplistic caricature in opposition — Hoffman (1989, p. 39) writes: “The neodarwinian paradigm therefore asserts that this history of life at all levels — including and even beyond the level of speciation and species extinction events, embracing all macroevolutionary phenomena — is fully accounted for by the processes that operate within pop­ulations and species.” I dedicate my book to refuting this traditional claim, and to advocating a helpful role for an independent set of macroevolutionary principles that expand, reformulate, operate in harmony with, or (at most) work orthogonally as additions to, the extrapolated, and persistently relevant (but not exclusive, or even dominant) forces of Darwinian microevolution.

  This perspective of synergy confutes the contrary, and ultimately destruc­tive, attempts by late 19th and early 20th century macroevolutionists to de­velop substitute mechanisms that would disprove or trivialize Darwinism, and that spread such a pall of suspicion over the important search for non-reductionistic and expansive evolutionary theories — a most unfortunate (if historically understandable) trend that stifled, for several generations, the unification and fruitful expansion of evolutionary theory to all levels and temporal tiers of biology. Thus, for example, my attempt to develop a specia-tional theory of macroevolution (Chapters 8 and 9), with species treated as irreducible Darwinian individuals playing causal roles analogous to those oc­cupied by organisms in Darwinian microevolution, represents an extension of Darwinian styles of explanation to another hierarchical level of analysis (with interestingly different causal twists and resulting patterns), not a refuta­tion of natural selection from an alien realm. (Such a speciational theory, however, does counter Hoffman's reductionistic claim of full theoretical suf­ficiency for “processes that operate within populations and species” — for, given the stasis of species under punctuated equilibrium, such macroevolu­tionary patterns originate by higher-order sorting among stable species, and not primarily by processes occurring anagenetically within the lifetime of these higher-level Darwinian individuals.) Similarly, the different rules of cat­astrophic mass extinctions require additions to the extrapolated Darwinian and microevolutionary causes of phyletic patterns, but do not refute or deny the relevance of conventional uniformitarian accretions through geological time. (In fact, a more comprehensive theory that seeks to integrate the rela­tive strengths, and interestingly disparate effects, of such different levels and forms of continuationist vs. catastrophic causality offers greater richness to Darwinian perspectives as both underpinnings and important contributors to a larger totality.)

  A second authorial input must arise from the distinctive ontogeny of past [Page 56] work. The Structure of Evolutionary Theory occupies a much broader terri­tory than my first lengthy technical book of an earlier career, Ontogeny and Phylogeny (1977b). The motivating conceit of the first book rested upon my choice of a much smaller compass defined by a much clearer tradition of definition and research. I thought — thus my designation of this strategy as a conceit — that I could quote, in extenso and from original sources, every im­portant statement, fr
om von Baer and before to de Beer and after, on the rela­tionship between development and evolution. This potential for comprehen­siveness brought me much pleasure and operational motivation.

  In fact, I soon realized that I could not succeed, even within this limited sphere — and I therefore punted shamelessly in the final result. I did manage to quote every important passage on the theoretical relationship between these central subjects of biology, but I passed, nearly completely, on the actual use of these putative relationships in specific proposals for phylogenetic recon­structions. And, as all historians of science and practitioners of evolutionary biology know, this genre of “phylogenizing” represented by far (at least by weight) the dominant expression of this theoretical rubric in the technical lit­erature. I would, by the way, defend my decision as entirely reasonable and proper, and not merely as practically necessary, because these specific phylo­genetic invocations made effectively no contribution to the development of evolutionary theory — my central concern in the book — and remained both speculative and transient to boot. But I do remember the humbling experi­ence of realizing that a truly full coverage could only represent a pipe dream, if applied to any important subject in a vigorous domain of research!

  My personal love of such thoroughness (with the necessary trade-off of limitation in domain) posed a substantial problem when I decided to expand my range from ontogeny and phylogeny to the structure of evolutionary the­ory. Of all genres in scholarship, I stand most strongly out of personal sympa­thy with broad-brush views that attempt to encompass entire fields (the his­tory of philosophy from Plato to Pogo, or of transportation from Noah to NASA) in a breathless summary paragraph for each of many thousand inci­dents. Even the most honorable efforts by great scholars — former Librarian of Congress Daniel Boorstin's The Explorers, for instance — make me cringe for simplistic legends repeated and interesting complexities omitted. At some level, truly important and subtle themes can only be misrepresented by such a strategy.

  But how then to treat the structure of evolutionary theory in a reputable, even an enlightening, way? Surely we cannot abandon all hope for writing honorably about such broad subjects simply because the genre of comprehen­sive listing by executive summary must propagate more mythology and mis­information than intrigue or understanding. As a personal solution to this crucial scholarly dilemma, and in developing the distinctive strategy of this book, I employed a device that I learned by doing, through many years of composing essays — a genre that I pursued by writing comprehensive personal treatments of small details, fully documentable in the space available, but [Page 57] also conveying important and general principles in their cascading implica­tions. I vowed that I would try to encompass the structure of evolutionary theory in its proper intellectual richness, but that I would do so by exhaustive treatment of well chosen exemplifying details, not by rapid summaries of in­adequate bits and pieces catalogued for all relevant participants.

  Under this premise, the central task then evolves (if I may use such a metaphor) into an extended exercise in discrimination. The solution may be la­beled as elitist, but how else can selection in intellectual history be under­taken? One must choose the best and the brightest, the movers and shakers by the sieve of history's harsh judgment (and not by the transiency of immedi­ate popularity) — and let their subtle and detailed formulations stand as a se­ries of episodes, each conveyed by an essay of adequate coverage. Luckily, the history of evolutionary thought — as one of the truly thrilling and expansive subjects of our mental lives — has attracted some of the most brilliant and fas­cinating doers and thinkers of intellectual history. Thus, we are blessed with more than adequate material to light the pathway of this particular odyssey in science. Luckily too, the founding figure of Darwin himself established such a clear basis of brave commitment that I could characterize, and then trace down to our own times, an essential logic that has defined and directed one of the most important and wide-ranging debates in the history of science into a coherent structure, ripe for treatment by my favored method of full coverage for the few truly central items (by knowing them through their fruits and logics, and by leaving less important, if gaudy, swatches gently aside in order to devote adequate attention to essential threads).

  A third, and final, authorial distinction — my treatment of history and my integration of the history of science with contemporary research on evolu­tionary theory — emerges directly from this strategy of coverage in depth for a small subset of essential items and episodes. My historical treatments tend to resolve themselves into a set of mini intellectual biographies (as exemplified and defended on page 46) for almost all the central players in the history of Darwinian traditions in evolutionary thought. I can only hope that this pecu­liar kind of intellectual comprehensiveness will strike some readers as enlight­ening for the “quick entree” thus provided into the essential work of the peo­ple who led, and the concepts that defined, the history of the greatest and most consequential revolution in the history of biological science. (In most cases — a Goethe, Cuvier, Weismann, de Vries, Fisher or Simpson, for exam­ple — I chose people for their intrinsic and transcendent excellence. In fewer instances — an Eimer or Hyatt as proponents of orthogenesis, for example — I selected eminently worthy scientists not as great general thinkers, but as best exponents of a distinctive approach to an important subject in the history of debate on essentials of evolutionary theory.)

  A few figures in history have been so prescient in their principal contribu­tion, and so acute and broad-ranging in their general perceptions, that they define (or at least intrude upon) almost any major piece of a comprehensive discussion (A. N. Whitehead famously remarked, for example, that all philosophy [Page 58] might be regarded as a footnote to Plato). Evolutionary biology pos­sesses the great good fortune to embrace such a figure — Charles Darwin, of course — at the center of its origin and subsequent history. Thus, Darwin emerges again and again, often controlling the logic of discussion, through­out this book — in his own full foundational exegesis (Chapter 2); but then, in later chapters, as the principal subject, and best possible exemplification, of other important subbranches on all three boughs of his essential logic (his re­luctant acceptance of higher levels of selection in Chapter 3; his formalist contrast to his own functionalism in stressing “correlations of growth” in Chapter 4; his views on direction and progress in the history of life in Chapter 6, and, even in the book's second half on modern developments, for his dis­cussion of discordance between historical origin and current utility as a point of departure for my treatment of exaptation in Chapter 11, and his attempt to underplay and undermine mass extinction as an introduction to my cri­tique of uniformitarianism and extrapolationism in the final Chapter 12). Who could ask for a more attractive and effective coordinating “device” to tie the disparate strands of such an otherwise disorderly enterprise together than the genial and brilliant persona of the man who first gave real substance to the grandeur in this view of life?

  Whatever my dubiety about the role and efficacy of abstracts (too often, as we would all admit in honest moments, our only contact with a work that we nonetheless then feel free to criticize in full assurance of our rectitude), I can­not deny that a work of this length, imbued moreover with a tendency to pen­etrate byways along a basic route that seems (at least to this author) ade­quately linear and logical, demands some attempt to list its principal claims in textual order. Hence, I now impose upon you the following abstract:

  Chapter 2: An exegesis of the origin

  1. All major pre-Darwinian evolutionary theories, Lamarck's in particu­lar, contrasted a primary force of linear progress with a distinctly secondary and disturbing force of adaptation that drew lineages off a main line into par­ticular and specialized relationships with immediate environments. In his most radical intellectual move, expressing both the transforming depth and the conceptual originality of the theory of natural selection, Darwin denied the existence of a
primary progressive force, while promoting the lateral force of adaptation to near exclusivity. In so privileging uniformitarian extrapola­tion as an explanatory device, Darwin imbued natural selection, the lateral force, with sufficient power to generate evolutionary change at all scales by accumulating tiny adaptive increments through the immensity of geological time.

  2. The Origin of Species exceeds all other scientific “classics” of past centu­ries in immediate and continued relevance to the basic theoretical formula­tions and debates of current practitioners. Careful exegesis of Darwin's logic and intentions, through textual analysis of the Origin, therefore assumes un­usual importance for the contemporary practice of science (not to mention its undeniable historical value in se). [Page 59]

  3. Darwin famously characterized the Origin as “one long argument” without explicitly stating “for what?” Assumptions about the focus of this long argument have ranged from the restrictively narrow (for natural selec­tion, or even for evolution) to the overly broad (for application of the most general hypotheticodeductive model in scientific argument, as Ghiselin has claimed). I take a middle position and characterize the “long argument” as an attempt to establish a methodological approach and intellectual foundation for rigorous analysis in historical science — a foundation that could then be used to validate evolution.

  4. The “long argument” for historical science operates at two poles — methodological and theoretical. The methodological pole includes a set of procedures for making strong inferences about phyletic history from data of an imperfect record that cannot, in any case, “see” past causes directly, but can only draw conclusions from preserved results of these causes. Darwin devel­ops four general procedures, all based on one of the three essential premises of his theory's central logic: the explanation of large-scale results by extrapo­lation from short-term processes. In order of decreasing information avail­able for making the required inference, these four procedures include: (1) ex­trapolation to longer times and effects of evolutionary changes actually observed in historic times (usually by analogy to domestication and horticul­ture); (2) exemplification and ordering of several phenomena as sequential stages of a single historical process (fringing reefs, barrier reefs and atolls as stages in the formation of coral reefs by subsidence of central islands, for ex­ample); (3) inference of history as the only conceivable coordinating explana­tion for a large set of otherwise disparate observations (consilience); and (4) inference of history from single objects based on quirks, oddities and imper­fections that must denote pathways of prior change.