Segue to Part Two
Contemporary challenges to all three central commitments of Darwinism (the legs of the tripod in my chosen metaphor, or the “essence” of the theory in the legitimate use of a word generally shunned by evolutionary biologists) prompted me to write this book. Such forms of debate set the mainsail of scholarly life, and cynics may be excused for suspecting the academic equivalent of glitz and grandstanding when their colleagues proclaim major unhappiness with received wisdom. This cynicism merits special attention when Charles Darwin serves as a target — for the demise of Darwinism has been trumpeted more often than the guard changes at Buckingham Palace, notwithstanding the evident fact that both seem to stand firm as venerable British institutions. (I state nothing new here: Kellogg (1907) began his wonderful book, the basis for my style of exposition, by refuting a German proclamation, then current, about the Sterbelager, or death-bed, of Darwinism — see Dennert, 1904, for an English translation of the book that inspired Kellogg's long and celebrated rejoinder.)
If continuity breeds respect — and what other criterion could an evolutionist propose in this volatile vale of tears? — then the most persuasive rejoinder to a charge of superficial and ephemeral grandstanding must lie in the documentation of long persistence and serious attention for a given critique. Persistence, of course, need not imply cogency; Lord only knows the lengthy pedigree of stupidity. But an analog to natural selection also operates in the world of ideas, and truly silly notions do get weeded out at certain levels of intellectual competence. Moreover, only a small subset of our forebears ranks as brilliant thinkers. When we can designate a critique as both longstanding in general and seriously supported by scholars in this subset, then such arguments should command our respect and attention. (Brilliance, of course, only implies cogency, not correctness. Cultural biases and simple lack of information can lead even the most gifted minds to firm convictions that seem risible today. But I do assert that brilliant scholars, while often as wrong as anyone else, devise their positions for interesting and instructive reasons. We may now reject Lyell's strict views about substantive uniformity, and Paley will find few modern devotees for his natural theology. But we must not write these men off — and we will learn much by studying the reasons for their distinctive attitudes.) [Page 586]
In this context, I ask readers to consider two points about the tripod of necessary support for Darwinism:
First, even during the period of current orthodoxy, beginning with the coalescence and spread of the Modern Synthesis; the three supports have never been particularly firm, or adequately defended. The first support — restriction of selection to the organismal level — received little explicit defense, but rather prevailed in a fuzzy sort of way by convention in practice. Sloppy statements implying group selection abounded in the literature (as documented in Chapter 7, pp. 544–556), and some disciplines, notably the classical ethology of Lorenz and his disciples, frequently cited arguments about supraorganismal selection without understanding their consequences for Darwinian theory. This situation changed dramatically when Wynne-Edwards (1962) advanced his explicit argument for group selection at a predominant relative frequency — and Williams (1966) wrote his spirited defense of the Darwinian straight and narrow by setting out the centrality of organismal selection so forcefully.
The second support — the validation of selection as a nearly exclusive mechanism of evolutionary change, as embodied in the adaptationist program — received strong verbal approbation, and elegant illustration in a few cases, but won orthodox status largely as a bandwagon effect prompted by the urgings of a few central figures, notably Mayr and Dobzhansky, and the subsequent acquiescence of most professionals to the assertion of such leading figures, and not to the data of convincing demonstrations (see Chapter 7 for a detailed defense of this claim, as embodied in my hypothesis on the “hardening” of the Modern Synthesis). In particular, taxonomic orthodoxy just before the Synthesis (Kinsey, 1936; Robson and Richards, 1936) regarded most geographic variation within species as nonadaptive. The opposite opinion triumphed as the Synthesis reached a height of prestige and orthodoxy, but few actual cases had been overturned by data. Rather, a shifting theoretical preference led to assertions of dominant relative frequency based on documentation inadequate to affirm either view. (I do not regard earlier arguments for nonadaptation as inherently more cogent. On the contrary, I am convinced that we still have no good idea about the relative frequencies of adaptive and nonadaptive effects in geographic variation. I only claim that the shift to adaptationist preferences resulted more from a bandwagon effect than from direct evidence — and that this second leg of the tripod therefore never enjoyed adequate buttressing.)
The third support — extrapolation, explicitly discussed here in terms of the surrogate proposition of geological uniformity, and so necessary to provide a stage that would nurture, or at least not disrupt, Darwin's hope for explaining the entire history of life by “pure” extension of principles derived from the small and palpable — prevailed more by assumption than by active validation, with Kelvin's defeat and Rutherford's proof of the earth's great age read as adequate defense (a logically insufficient argument, by the way, because time may be long, but change still concentrated in rare catastrophic episodes). By the largely arbitrary and contingent sociology of disciplines, paleontology [Page 587] belonged to the geologists, and students of fossils therefore received virtually no training in evolution. With few exceptions, notably the work of G. G. Simpson, paleontology (at least during the first half of the 20th century) played little role in the development of a theory to account for its own subject matter.
Second, and more important in summarizing the first half of this book: not only can we identify basic logical weaknesses in standard defenses for the three Darwinian supports, but cogent critiques have also been persistent, indeed omnipresent though changing in form, throughout the history of evolutionary thought. These histories may not be widely known to current practitioners, but the best minds of our profession have struggled continuously with themes of the essential tripod — and their arguments deserve our attention and respect. (Without this knowledge, we tend to imbue orthodoxies with false permanence or, even worse, to lose sight of basic principles in the surrounding silence, thereby converting dubious but central postulates into hidden assumptions. History can and should be liberating.)
For the first leg of the tripod of essential support, hierarchy theory and multiple levels of selection do not represent only a modern gloss upon Darwinism. Rather, contemporary versions of these concepts have reinvigorated the oldest issue of our profession. In Chapter 3, I showed that the first two evolutionary systems well known to English-speaking naturalists — Lamarck's and Chambers's — relied on a causal hierarchy that contrasted progress with diversification. Darwin explicitly combatted these ideas with a single-level theory based on extrapolating the small and observable results of natural selection, operating on organisms in local populations, to render all evolutionary phenomena at all scales of time and effect. Weismann, and Darwin himself as he struggled to explain diversity, then considered hierarchical models of selection formulated very much in the spirit of modern versions. Weismann, after much internal debate, leading to eventual rejection of his previous commitment to the strict Darwinism of single-level selection on organisms alone, eventually advocated a full hierarchy of levels, explicitly citing this concept as the most distinctive innovation and centerpiece of his mature evolutionary views.
The internalist critique of adaptationism (the main subject of modern criticism on the second, or “creativity,” leg of the tripod) boasts an even more venerable pedigree. I showed, in Chapters 4 and 5, how this critique defined the major difference between British (Paleyan) and continental versions of natural theology in preevolutionary days. I then demonstrated that the same division, transformed as the structuralist-functionalist dichotomy, served as a focus for evolution
ary debate — pitting the functionalism (adaptationism) of such disparate theories as Darwinian selectionism and Lamarckian soft inheritance against the great continental schools of structuralism, as advocated by such scientists as Goethe (and most of the German Naturphilosophen), Geoffroy Saint-Hilaire (and the French transcendental morphologists), and, in a rare move across the Channel, in major themes of the complex and much misunderstood evolutionary views of Richard Owen. Finally, I traced the two [Page 588] major lines of post-Darwinian internalist thought (orthogenesis and saltationism), and documented the continuity of this pedigree, after the Mendelian rediscovery, in the macromutationism of Hugo de Vries and (combining both strands of constraint and saltation) in the apostasy of Richard Goldschmidt. Modern critiques of adaptationism rest upon an ancient legacy.
For the third leg of extrapolationism, as illustrated here by the surrogate theme of Darwin's geological needs (for the other major aspects of extrapolationism fall into the theoretical domains of the first two essential postulates), I showed, in Chapter 6, that classical catastrophism operated as good science, and also represented the literal empiricism of its time. I then argued that Lyell's uniformitarian victory arose largely as a triumph of skilled but dubious rhetoric. The aspects of catastrophism that posed the strongest challenges to Darwin's ideas on the origin of macroevolutionary pattern never received a convincing critique, and have now experienced a legitimate rebirth in modern views on mass extinction.
Nonetheless, although each leg of the Darwinian tripod faces a venerable indictment from the fullness of history, the path of modern reform surely does not lie with these classical critiques, for each embodies fatal flaws in each of two debilitating ways:
Anchors in cultural biases. The attempt to validate human superiority by the doctrine of progress identifies the heaviest burden imposed by Western culture upon evolutionary views of all stripes. In their nineteenth century versions, all three critiques of the essential postulates of Darwinism sunk their major root (and fallacy) in the concept of progress. For the first leg, the original hierarchical models of Lamarck and Chambers construed their higher level of large-scale change as a force of progress orthogonal to a palpable cause of local adaptation. For both Lamarck and Chambers, the two forces of general progress and local adaptation are not only geometrically orthogonal (upwards vs. sidewards), but also conceptually opposed, as the lateral force “pulls” lineages from their upward course into dead ends of local specialization. For the second leg, most structuralist visions postulated an inherent increase of complexity and progress mediated by laws of form and internal principles of living matter. These internalist theories proved attractive because, in contrast with the Darwinian contingency of shifting local adaptation, they offered more promise as validations for the great psychic balm of progress. On the third leg, catastrophism might seem inherently opposed to ideas of regulated and predictable increase in life's complexity, but the classical versions advocated an intimate connection between progressionism and paroxysmal change — for pre-Darwinian catastrophists generally postulated renewed faunas of increasing excellence after each episode of extinction. This theme became such an intrinsic component of classical catastrophism that many scholars now designate this movement as the “directionalist synthesis” or as “progressionism,” and not by the paroxysmal dynamics of catastrophic change.
Failures of logic. The three critiques, in their nineteenth century versions, are explicitly anti-Darwinian. That is, they propose alternative [Page 589] causes of evolution that either deny natural selection entirely, or demote Darwin's preferred cause to insignificance. These alternative forces are, in any case, opposed to — clearly not synergistic with — Darwin's principle of natural selection at the organismic level.
The explicit, often vociferous, invocation of these critiques against Darwinism set the primary agenda for scientific debate from the very beginning of modern evolutionary theory. On the first leg, the Lamarck-Chambers tradition of a primary force of progress (effectively inaccessible to empirical study), opposed to a palpable cause of immediate adaptation (eminently operational for research, but decidedly secondary in significance), acted as a major spur to Darwin's development of a fully operational theory with causes working at a single and accessible level. On the second leg, internalist notions of orthogenesis and saltation denied creativity to natural selection and defined the major versions of late 19th century anti-Darwinism. On the third leg, classical catastrophism became Darwin's personal bete noire, an obstacle that he surmounted by allegiance to Lyellian uniformity. Later in Darwin's career, the appearance of a similar threat in a different guise — the claim for an earth too young to render the results of evolution by natural selection in a gradualistic mode — led Darwin to characterize Lord Kelvin as an “odious specter.”
I believe that the historical tradition for using these critiques as supposed confutations of Darwinism has engendered a great deal of unnecessary and unproductive wrangling in our own time, as markedly different versions of the same critiques needlessly evoke old fears. I also believe that we can find the way to a better (and healing) taxonomy by following the lead of Kellogg's fine presentation (1907), already much praised in this book. Kellogg, as previously discussed (pp. 163–169), divided critical commentary about Darwinism into arguments “auxiliary to” and “alternative to” natural selection — enlargements and confutations, if you will. In the past, critiques of the Darwinian tripod have usually been advocated in Kellogg's alternative, or destructive, mode — and a tradition for quick (often ill-considered) and defensive reaction by Darwinians has developed whenever the critical buzz-words rise again: rapid change, group selection, mass extinction, directed mutation, for example. But all these critiques can also generate powerful versions in Kellogg's auxiliary, or helpful and expansive, mode — as Kellogg himself recognized when he classified Weismann's theory of hierarchy as one of the two most significant auxiliary propositions of his time.
The older, alternative mode of these critiques did lead to a series of dead ends, rightly rejected by the resurgent Darwinism of the Modern Synthesis. Older versions of hierarchy (the first leg) foundered in the mysticism of super-organisms and harmonious ecologies; constraint and laws of form (the second leg) became mired in invalid macromutationism or lingering orthogenesis; catastrophic geology (representing the third leg) languished in the failure of all proposed mechanisms for global paroxysm. The old versions, freighted by the cultural bias of progress, and rooted in false arguments for the demise of Darwinism, richly deserved the rejection they received. [Page 590]
But modern forms of these critiques are now being advanced in different and helpful versions within Kellogg's auxiliary mode — that is, as ideas to expand, while substantially changing, the Darwinian core. For the first leg, and most importantly, the hierarchical theory of multi-level selection retains Darwin's emphasis on the centrality of selection as a mechanism, but rejects the notion that the organismal level must hold nearly exclusive sway as a causal locus of change (while wondering if this conventional Darwinian level can even claim dominant status — Chapters 8 and 9). On the second leg, modern ideas of constraint and channeling deny the crucial isotropy of variation, so necessary to the logic of selection as the primary directional force in evolution, and therefore envision important roles for structural and internal causes as patterning agents of evolutionary change (Chapters 10 and 11). These internal channels work with selection as conduits for its impetus — that is, as auxiliary (not alternative) forces to natural selection. For the third leg, current notions of mass extinction do not challenge the Darwinian mechanism of selection per se, but suggest that any full explanation of macroevolutionary pattern must integrate the accumulated Darwinian effects of normal times with the profound restructurings of diversity that occur in environmental episodes too rapid or too intense for adaptive response by many species and clades (Chapter 12).
Therefore, in modern versi
ons of the three critiques, classical Darwinism either becomes expanded (in the theory of hierarchical selection), or dynamically counterposed with other causal forces working in concert with selection to produce the patterns of life's history, either at a conventional microevolutionary scale (internal channels as conduits for selection) or as interacting regimes through geological time (mass extinctions and selective replacements). But we cannot fairly portray these expanded views as pure sweetness and light for orthodox Darwinism. Much that has been enormously comfortable must be sacrificed to accept this enlarged theory with a retained Darwinian core — particularly the neat and clean, the simple and unifocal, notion that natural selection on organisms represents the cause of evolutionary change, and (by extrapolation) the only important agent of macroevolutionary pattern.
On the first leg, the theory of hierarchical selection differs substantially from classical Darwinism in basic logic and concept — for explanations of both stability and change must now be framed as compound results of a balanced interaction of levels, working in all possible ways (in concert, in conflict, or orthogonally), and not as shifting optimalities built at a single level. On the second leg, an emphasis on constraints and channels implies a new set of operational concerns, and a revamping of the evolutionary research program. Internally imposed biases upon directions of change become a major subject for study — and the role of developmental patterns must again become prominent in evolutionary theory. (I must confess great personal pleasure in observing the rapid progress of this integration, as the wall between these two subjects seemed so frustratingly impenetrable when I published my first book, Ontogeny and Phylogeny, not so long ago in 1977.) On the third leg, a renewed [Page 591] appreciation for the shaping power of mass extinction must reinstate paleontology as a source of theory, and not merely a repository for the historical unfolding of processes fully illuminated by microevolutionary studies. Thus, the new theory produced by the confluence of these critiques and their integration with classical Darwinism will not emerge from a simple act of generosity or noblesse oblige by previous orthodoxy. The new theory may remain Darwinian in spirit (a “higher Darwinism,” see Gould, 1982b), but its development requires a wrenching from several key assumptions of classical Darwinism — not simply a smooth evolution from conventional precepts — as embodied in both the tripod of essential theoretical support, and the methodology of uniformitarian extrapolation (the theoretical and methodological poles of Darwinism, as discussed in Chapter 2).
The Structure of Evolutionary Theory Page 94
