The Structure of Evolutionary Theory Read online

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  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 [Page 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 radical

  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.

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  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 [Page 7] described 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 Hu
ll's decision to treat theories as “things,” or individuals in the crucial sense of coherent historical entities — and in opposition to the [Page 8] standard tactic, in conventional scholarship on the “history of ideas,” of tracing the chronology of expression for entirely abstract concepts defined only by formal similarity of content, and not at all by ties of historical continuity, or even of mutual awareness among defenders across centuries and varied cul­tures. (For example, Hull points out that such a conventional history of the “chain of being” would treat this notion as an invariant and disembodied Platonic archetype, independently “borrowed” from the eternal storehouse of potential models for natural reality, and then altered by scholars to fit local contexts across millennia and cultures.)

  But I believe that Hull's laudable desire to recast the history of ideas as a narrative of entities in historical continuity, rather than as a disconnected chronology of tidbits admitted into a class only by sufficient formal similarity with an abstract ideological archetype, then leads him to an undervaluation of actual content. Hull exemplifies his basic approach (1988, p. 17): “A con­sistent application of what Mayr has termed 'population thinking' requires that species be treated as lineages, spatiotemporally localized particulars, in­dividuals. Hence, if conceptual change is to be viewed from an evolutionary perspective, concepts must be treated in the same way. In order to count as the 'same concept,' two term-tokens must be part of the same conceptual lin­eage. Population thinking must be applied to thinking itself.”

  So far, so good. But Hull now extends this good argument for the necessity of historical connectivity into a claim for sufficiency as well — thus springing a logical trap that leads him to debase, or even to ignore, the “morphology” (or idea content) of these conceptual lineages. He states that he wishes to “organize term-tokens into lineages, not into classes of similar term-types” (pp. 16-17). I can accept the necessity of such historical continuity, but nei­ther I nor most scholars (including practicing scientists) will then follow Hull in his explicit and active rejection of similarity in content as an equally neces­sary criterion for continuing to apply the same name — Darwinian theory, for example — to a conceptual lineage.

  At an extreme that generates a reductio ad absurdum for rejecting Hull's conclusion, but that Hull bravely owns as a logical entailment of his own prior decision, a pure criterion of continuity, imbued with no constraint of content, forces one to apply the same name to any conceptual lineage that has remained consciously intact and genealogically unbroken through several generations (of passage from teachers to students, for example), even if the current “morphology” of concepts directly inverts and contradicts the central arguments of the original theory. “A proposition can evolve into its contra­dictory,” Hull allows (1988, p. 18). Thus, on this account, if the living intel­lectual descendants of Darwin, as defined by an unbroken chain of teaching, now believed that each species had been independently created within six days of 24 hours, this theory of biological order would legitimately bear the name of “Darwinism.” And I guess that I may call myself kosher, even though I and all members of my household, by conscious choice and with great ideo­logical fervor, eat cheeseburgers for lunch every day — because we made this [Page 9] dietary decision in a macromutational shift of content, but with no genealogi­cal break in continuity, from ten previous generations of strict observers of kashrut.

  The objections that most of us would raise to Hull's interesting proposition include both intellectual and moral components. Certain kinds of systems are, and should be, defined purely by genealogy and not at all by content. I am my father's son no matter how we interact. But such genealogical defini­tions, as validated by historical continuity, simply cannot adequately charac­terize a broad range of human groupings properly designated by similarity in content. When Cain mocked God's inquiry about Abel's whereabouts by ex­claiming “Am I my brother's keeper” (Genesis 4:9), he illustrated the appro­priateness of either genealogy by historical connection or fealty by moral re­sponsibility as the proper criterion for “brotherhood” in different kinds of categories. Cain could not deny his genealogical status as brother in one sense, but he derided a conceptual meaning, generally accorded higher moral worth as a consequence of choice rather than necessity of birth, in disclaim­ing any responsibility as keeper. As a sign that we have generally privileged the conceptual meaning, and that Cain's story still haunts us, we need only re­member Claudius's lament that his murder of his own brother (and Hamlet's father) “hath the primal eldest curse upon't.”

  Ordinary language, elementary logic, and a general sense of fairness all combine to favor such preeminence for a strong component of conceptual continuity in maintaining a name or label for a theory. Thus, if I wish to call myself a Darwinian in any just or generally accepted sense of such a claim, I do not qualify merely by documenting my residence within an unbroken lin­eage of teachers and students who have transmitted a set of changing ideas organized around a common core, and who have continued to study, aug­ment and improve the theory that bears such a longstanding and honorable label. I must also understand the content of this label myself, and I must agree with a set of basic precepts defining the broad ideas of a view of natural real­ity that I have freely chosen to embrace as my own. In calling myself a Dar­winian I accept these minimal obligations (from which I remain always and entirely free to extract myself should my opinions or judgments change); but I do not become a Darwinian by the mere default of accidental location within a familial or educational lineage.

  Thus, if we agree that a purely historical, entirely content-free definition of allegiance to a theory represents “too little” commitment to qualify, and that we must buttress any genealogical criterion with a formal, logical, or anatom­ical definition framed in terms of a theory's intellectual content, then what kind or level of agreement shall we require as a criterion of allegiance for in­clusion? We now must face the opposite side of Goldilocks's dilemma — for once we advocate criteria of content, we do not wish to impose such strin­gency and uniformity that membership becomes more like a sworn obedience to an unchanging religious creed than a freely chosen decision based on per­sonal judgment and perception of intellectual merits. My allegiance to [Page 10] Darwinian theory, and my willingness to call myself a Darwinian biologist, must not depend on my subscription to all 95 articles that Martin Luther nailed to the Wittenburg church door in 1517; or to all 80 items in the Syllabus of Er­rors that Pio Nono (Pope Pius IX) proclaimed in 1864, including the “fal­lacy,” so definitionally uncongenial to science, that “the Roman Pontiff can and should reconcile himself to and agree with progress, liberalism and mod­ern civilization”; or to all 39 articles of the Church of England, adopted by Queen Elizabeth in 1571 as a replacement for Archbishop Thomas Cranmer's 42 articles of 1553.

  Goldilocks's “just right” position between these extremes will strike nearly all cooperatively minded intellectuals, committed to the operationality and advance of their disciplines, as eminently sensible: shared content, not only historical continuity, must define the structure of a scientific theory; but this shared content should be expressed as a minimal list of the few defining at­tributes of the theory's central logic — in other words, only the absolutely es­sential statements, absent which the theory would either collapse into fallacy or operate so differently that the mechanism would have to be granted an­other name.

  Now such a minimal list of such maximal centrality and importance bears a description in ordinary language — but its proper designation requires that evolutionary biologists utter a word rigorously expunged from our profes­sional consciousness since day one of our preparatory course work: the con­cept that dare not speak its name — essence, essence, essence (say the word a few times out loud until the fear evaporates and the laughter recedes). It's high time that we repressed our aversion to this good and honorable word. Theories have essences. (So, by the way, and in a more restrictive and nuanced sense, do organisms — in
their limitation and channeling by con­straints of structure and history, expressed as Bauplane of higher taxa. My critique of the second theme of Darwinian central logic, Chapters 4–5 and 10–11, will treat this subject in depth. Moreover, my partial defense of or­ganic essences, expressed as support for structuralist versions of evolutionary causality as potential partners with the more conventional Darwinian functionalism that understandably denies intelligibility to any notion of an es­sence, also underlies the double entendre of this book's title, which honors the intellectual structure of evolutionary theory within Darwinian traditions and their alternatives, and which also urges support for a limited version of structuralist theory, in opposition to certain strict Darwinian verities.)

  Our unthinking rejection of essences can be muted, or even reversed into propensity for a sympathetic hearing, when we understand that an invocation of this word need not call down the full apparatus of an entirely abstract and eternal Platonic eidos — a reading of “essence” admittedly outside the logic of evolutionary theory, and historical modes of analysis in general. But the solu­tion to a meaningful notion of essence in biology lies within an important epi­sode in the history of emerging evolutionary views, a subject treated exten­sively in Chapter 4 of this book, with Goethe, Etienne Geoffroy St. Hilaire, and Richard Owen as chief protagonists. [Page 11]