The Structure of Evolutionary Theory Read online

  To complement this most general statement with just one example of the utility of historical analysis at the smaller scale of details, I offer the following case as the strongest argument for my central claim that Darwin's brave at­tempt to construct a single-level, exclusively organismic theory of natural se­lection must fail in principle, and that all selectionists must eventually own a hierarchical model. What better evidence can we cite than the historical dem­onstration (see Chapters 3 and 5 for details) that each of the only three foundational thinkers who truly understood the logic of selectionism — August Weismann, Hugo de Vries, and Charles Darwin himself — tried mightily to make the single-level version work as a fully sufficient explanation for evolu­tion. And each failed, after intense intellectual struggle, and for fascinatingly different reasons documented later in the book — Darwin for explaining di­versity by reluctant resort to species selection; Weismann for a strongest ini­tial commitment to a single level, and an eventual recognition of full hierar­chy as the most important and distinctive conclusion of his later career (by his own judgment); and de Vries for reconciling his largely psychological fealty to Darwin as his intellectual hero, with his clearly non-Darwinian account of the origin of species and the explanation of trends (including an explicit coin­ing of the term “species selection” for explaining cladal patterns).

  One might cite various truisms telling us that people ignorant of history will be condemned to repeat its errors. But I would rather re-express this ac­curate and rueful observation in a more positive manner by illustrating the power of historical analysis to aid both our current understanding and the depth of our appreciation for the intellectual importance of our enterprise. Finally, and to loosen the rein on personal bravado that I usually try to hold at least somewhat in check, no scholar should impose a project of this length upon his colleagues unless he believes that some quirk of special skill or expe­rience permits him to proceed in a unique manner that may offer some insight to others. In my case, and only by history's fortune of no immediate competi­tion in a small field, I may be able to combine two areas of professional com­petence not otherwise conjoined among current evolutionists. I am not a credentialed historian of science, but I believe that I have done sufficient work in this field (with sufficient understanding of the difference between the Whiggish dilettantism of most enthusiastic amateurs, and the rigorous meth­ods applied by serious scholars) to qualify as adequately knowledgeable. (At least I can read all the major works in their original languages, and I stay close to the “internalist” style of analysis that people who understand the logic and history of theories, but cannot claim truly professional expertise in the “externalist” factors of general social and historical context, can usefully pursue.) Meanwhile I am, for my sins, a lifelong and active professional pale­ontologist, a commitment that began at age five as love at first sight with a di­nosaur skeleton.

  Many historians possess deeper knowledge and understanding of their immediate subject than I could ever hope to acquire, but none enjoy enough [Page 37] intimacy with the world of science (knowing its norms in their bones, and its quirks and foibles in their daily experience) to link this expertise to contem­porary debates about causes of evolution. Many more scientists hold superb credentials as participants in current debates, but do not know the historical background. As I hope I demonstrated by practical utility in The Mismeasure of Man (Gould, 1981a), a small and particular — but I think quite impor­tant — intellectual space exists, almost entirely unoccupied, for people who can use historical knowledge to enlighten (not merely to footnote or to pret­tify) current scientific debates, and who can then apply a professional's “feel” for the doing of science to grasp the technical complexities of past debates in a useful manner inaccessible to historians (who have therefore misinter­preted, in significant ways, some important incidents and trends in their sub­ject). I only hope that I have not been wrong in believing that my devotion of a lifetime's enthusiasm to both pursuits might make my efforts useful, in a distinctive way, to my colleagues.

  Theory

  I admire my friend Oliver Sacks extravagantly as a writer, and I could never hope to match him in general quality or human compassion. He once said something that touched me deeply, despite my continuing firm disagreement with his claim (while acknowledging the validity of the single statement rele­vant to the present context). Oliver said that he envied me because, although we had both staked out a large and generous subject for our writing (he on the human mind, me on evolution), I had enjoyed the privilege of devising and developing a general theory that allowed me to coordinate all my work into a coherent and distinctive body, whereas he had only written descrip­tively and aimlessly, albeit with some insight, because no similar central focus underlay his work. I replied that he had surely sold himself short, because he had been beguiled by conventional views about the nature and limits of what may legitimately be called a central scientific theory — and that he certainly held such an organizing concept in his attempt to reintroduce the venerable “case study method” of attention to irreducible peculiarities of individual pa­tients in the practice of cure and healing in medicine. Thus, I argued, he held a central theory about the importance of individuality and contingency in gen­eral medical theory, just as I and others had stressed the centrality of histori­cal contingency in any theoretical analysis and understanding of evolution and its actual results.

  Oliver saw the theory of punctuated equilibrium itself, which I developed with Niles Eldredge and discuss at inordinate length in Chapter 9, as my coordinating centerpiece, and I would not deny this statement. But punctuated equilibrium stands for a larger and coherent set of mostly iconoclastic con­cerns, and I must present some intellectual autobiography to explain the rea­sons and the comings together, as best I understand them myself — hence my rip-off of Cardinal Newman's famous title for the best similar effort ever made, albeit in a maximally different domain. In his Apologia Pro Vita Sua (an apology for one's own life), Newman intends the operative word as I do, [Page 38] in its original and positive meaning, not in the currently more popular nega­tive sense — “something said or written in defense or justification of what ap­pears to others to be wrong or of what may be liable to disapprobation” (per Webster's).

  As my first two scientific commitments, I fell in love with paleontology when I met Tyrannosaurus in the Museum of Natural History at age five, and with evolution at age 11, when I read G. G. Simpson's The Meaning of Evolu­tion, with great excitement but minimal comprehension, after my parents, as members of a book club for folks with intellectual interests but little eco­nomic opportunity or formal credentials, forgot to send back the “we don't want anything this month” card, and received the book they would never have ordered (but that I begged them to keep because I saw the little stick fig­ures of dinosaurs on the dust jacket). Thus, from day one, my developing pro­fessional interests united paleontology and evolution. For some reason still unclear to me, I always found the theory of how evolution works more fasci­nating than the realized pageant of its paleontological results, and my major interest therefore always focused upon principles of macroevolution.* I did come to understand the vague feelings of dissatisfaction (despite Simpson's attempt to resolve them in an orthodox way by incorporating paleontology within the Modern Synthesis) that some paleontologists have always felt with the Darwinian premise that microevolutionary mechanics could construct their entire show just by accumulating incremental results through geological immensity.

  As I began my professional preparation for a career in paleontology, this vague dissatisfaction coagulated into two operational foci of discontent. First (and with Niles Eldredge, for we worried this subject virtually to death as graduate students), I became deeply troubled by the Darwinian convention that attributed all non-gradualistic literal appearances to imperfections of the geological record. This traditional argument contained no logical holes, but the practical consequences struck me as unacceptable (esp
ecially at the out­set of a career, full of enthusiasm for empirical work, and trained in statis­tical techniques that would permit the discernment of small evolutionary [Page 39] changes). For, by the conventional rationale, the study of microevolution be­came virtually nonoperational in paleontology — as one almost never found this anticipated form of gradual change up geological sections, and one there­fore had to interpret the vastly predominant signal of stasis and geologically abrupt appearance as a sign of the record's imperfection, and therefore as no empirical guide to the nature of evolution. Second, I became increasingly dis­turbed that, at the higher level of evolutionary trends within clades, the ma­jority of well documented examples (reduction of stipe number in graptolites, increasing symmetry of crinoidal cups, growing complexity of ammonoid su­tures, for example) had never been adequately explained in the terms de­manded by Darwinian convention — that is, as adaptive improvements of constituent organisms in anagenetic sequences. Most so-called explana­tions amounted to little more than what Lewontin and I, following Kipling, would later call “just-so stories,” or plausible claims without tested evidence, whereas other prominent trends couldn't even generate a plausible story in adaptationist terms at all.

  As Eldredge and I devised punctuated equilibrium, I did use the theory to resolve these two puzzles to my satisfaction, and each resolution, when finally generalized and further developed, led to my two major critiques of the first two branches of the essential triad of Darwinian central logic — so Oliver Sacks's identification of punctuated equilibrium as central to my theoretical world holds, although more as a starting point than as a coordinating focus. By accepting the geologically abrupt appearance and subsequent extended stasis of species as a fair description of an evolutionary reality, and not only as a sign of the poverty of paleontological data, we soon recognized that spe­cies met all criteria for definition and operation as genuine Darwinian indi­viduals in the higher-level domain of macroevolution — and this insight (by complex routes discussed in Chapter 9) led us to concepts of species selection in particular and, eventually, to the full hierarchical model of selection as an interesting theoretical challenge and contrast to Darwinian convictions about the exclusivity of organismal selection. In this way, punctuated equilibrium led to the reformulation proposed herein for the first branch of essential Dar­winian logic.

  Meanwhile, in trying to understand the nature of stasis, we initially fo­cused (largely in error, I now believe) upon internal constraints, as vaguely represented by various concepts of “homeostasis,” and as exemplified in the model of Galton's polyhedron (see Chapter 4). These thoughts led me to extend my doubts about adaptation and the sufficiency of functionalist mechanisms in general — especially in conjunction with my old worries about paleontological failures to explain cladal trends along traditional adapta­tionist lines. Thus, these aspects of punctuated equilibrium strongly contrib­uted to my developing critiques of adaptationism and purely functional me­chanics on the second branch of essential Darwinian logic (although other arguments struck me as even more important, as discussed below).

  Nonetheless, and despite the centrality of punctuated equilibrium in developing a broader critique of conventional Darwinism, my sources extended [Page 40] outward into a diverse and quirky network of concerns that seemed, to me and at first, isolated and uncoordinated, and that only later congealed into a coherent critique. For this curious, almost paradoxical, reason, I have be­come even more convinced that the elements of my overall critique hang to­gether, for I never sensed the connections when I initially identified the com­ponents as, individually, the most challenging and intriguing items I had encountered in my study of evolution. When one accumulates a set of things only for their independent appeals, with no inkling that any common intellec­tual ground underlies the apparent miscellany, then one can only gain con­fidence in the “reality” of a conceptual basis discerned only later for the cohe­sion. I would never argue that this critique of strict Darwinism gains any higher probability of truth value for initially infecting me in such an uncoor­dinated and mindless way. But I would assert that a genuinely coherent and general alternative formulation must exist “out there” in the philosophical universe of intellectual possibilities — whatever its empirical validity — if its isolated components could coagulate, and be discerned and selected, so un­consciously.

  If I may make a somewhat far-fetched analogy to my favorite Victorian novel, Daniel Deronda (the last effort of Darwin's friend George Eliot), the hero of this story, a Jew raised in a Christian family with no knowledge of his ethnic origins, becomes, as an adult, drawn to a set of apparently inde­pendent activities with no coordinating theme beyond their relationship, en­tirely unknown to Deronda at the time of his initial fascination, to Jewish history and customs. Eventually, he recognizes the unifying theme behind such apparent diversity, and learns the truth of his own genetic background. (I forgive Eliot for this basically silly fable of genealogical determinism be­cause her philosemitic motives, however naive and a bit condescending, shine forth so clearly in the surrounding antisemitic darkness of her times.) But I do feel, to complete the analogy, rather like a modern, if only culturally or psy­chologically predisposed, Deronda who gathered the elements of a coherent critique solely because he loved each item individually — and only later sensed an underlying unity, which therefore cannot be chimaerical, but may claim some logical existence prior to any conscious formulation on my part.

  In fact, the case for an external and objective coherence of this alternative view of evolution seems even stronger to me because I gathered the indepen­dent items not only in ignorance of their coordination, but also at a time when I held a conscious and conventional view of Darwinian evolution that would have actively denied their critical unity and meaning. I fledged in sci­ence as a firm adaptationist, utterly beguiled by the absolutist beauty (no doubt, my own simplistic reading of a more subtle, albeit truly hardened, Modern Synthesis) of asserting, a la Cain and other ecological geneticists of the British school, that all aspects of organismal phenotypes, even the most trivial nuances, could be fully explained as adaptations built by natural selec­tion.

  I remember two incidents of juvenilia with profound embarrassment to­day: First, an undergraduate evening bull session with the smartest physics [Page 41] major at Antioch College, as his skepticism evoked my stronger insistence that our science matched his in reductionistic rigor because “we” now knew for certain that natural selection built everything for optimal advantage, thus making evolution as quantifiable and predictive as classical physics. Second, as a somewhat more sophisticated, but still beguiled, assistant professor, I re­member my profound feeling of sadness and disappointment, nearly amount­ing to an emotional sense of betrayal, upon learning that an anthropological colleague favored drift as the probable reason for apparently trivial genetic differences among isolated groups of Papua-New Guinea peoples. I remem­ber remonstrating with him as follows: Of course your argument conforms to logic and empirical possibility, and I admit that we have no proof either way. But your results are also consistent with selection — and our panselectionist paradigm has forged a theory of such beauty and elegant simplicity that one should never favor exceptions for their mere plausibility, but only for docu­mented necessity. (I recall this discussion with special force because my emo­tional feelings were so strong, and my disappointment in his “unnecessary apostasy” so keen, even though I knew that neither of us had the empirical “goods.”) Finally, if I could, in a species of Devil's bargain, wipe any of my publications off the face of the earth and out of all memory, I would gladly nominate my unfortunately rather popular review article on “Evolutionary paleontology and the science of form” (Gould, 1970a) — a ringing paean to selectionist absolutism, buttressed by the literary barbarism that a “quantifunctional” paleontology, combining the best of biometric and mechanical analyses, could prove panadaptationism even for fossils that could not be run through the hoops of actu
al experiments.

  Against this orthodox background — or, rather, within it and quite unconsciously for many years — I worked piecemeal, producing a set of separate and continually accreting revisionary items along each of the branches of Darwinian central logic, until I realized that a “Platonic” something “up there” in ideological space could coordinate all these critiques and fascinations into a revised general theory with a retained Darwinian base.

  The first branch of levels in selection proceeded rather directly and linearly because the generality flowed so clearly from punctuated equilibrium itself, once Eldredge and I finally worked through the implications and extensions of our own formulations (Eldredge and Gould, 1972). Steve Stanley (1975) and Elisabeth Vrba (1980) helped to show us what we had missed in rami­fications leading from the phenomenology of stasis and geologically abrupt appearance, to recognizing species as genuine Darwinian individuals, to des­ignating species as, therefore and potentially, the basic individuals of macro-evolution (comparable with the role of the organism in microevolution), to the validity of species selection, and eventually to the full hierarchical model and its profound departure from the exclusively organismal accounts of con­ventional Darwinism (or the even more reduced and equally monistic genic versions of Williams and Dawkins) — see Vrba and Gould, 1986. Finally, by adopting the interactor rather than the replicator approach to defining selec­tion, and by recognizing emergent fitness, rather than emergent characters, as [Page 42] the proper criterion for identifying higher-level selection (Lloyd and Gould, 1993; Gould and Lloyd, 1999), I think that we finally reached, by a circuitous route around many stumbling blocks of my previous stupidity, a consistent and truly operational theory of hierarchical selection (see Chapter 8).