The Structure of Evolutionary Theory

by Stephen Jay Gould

  Richard Goldschmidt understood all the connections and, however flawed the result, developed a coherent theory for a full internalist alternative to gradualist and Darwinian functionalism, a view that integrated both themes — facet-flipping and channeling — of Galton's polyhedron. Gold­schmidt became the chief focus for vocal opposition by the synthesists, a sym­bol for all the bad old ways of outdated, typological thinking. I do not write to defend his specific ideas. The particulars of his genetic theory were deeply wrong, and disproved even in his lifetime, though he would not change his commitments. But I do maintain that his fully articulated critique remains as powerful as ever, and must be integrated with Darwinian orthodoxy to form a true and higher synthesis. In choosing Goldschmidt as the focus of their de­rision, the synthesists selected the right person for the best reason of all: Goldschmidt developed and fully understood all pieces of the critique, and he knew how the arguments cohered. Does the best fit always survive?

  We need iconoclasts, if only to keep us thinking and probing. At the end of the Two Minutes Hate in 1984, Emmanuel Goldstein's “hostile figure melted into the face of Big Brother, . . . full of power and mysterious calm, and so vast that it almost filled up the screen. Nobody heard what Big Brother was saying. It was merely a few words of encouragement, the sort of words that are uttered in the din of a battle, not distinguishable individually but restor­ing confidence by the fact of being spoken.” Ignorance is not strength.

  [Page 467]

  CHAPTER SIX

  Pattern and Progress on

  the Geological Stage

  Darwin and the Fruits of Biotic Competition

  A GEOLOGICAL LICENSE FOR PROGRESS

  A plethora of mottoes reminds us that political revolutions are never tidy — not a gentleman says one, no good omelette without cracking eggshells says another. Intellectual revolutions may avoid trails of blood (or they may not, at least metaphorically), but transitions in ideas can become as messy and complex as overthrows of temporal government. One world cannot be sub­stituted for another without leaving some loose ends and some substantial pieces of an uncompleted puzzle.

  Darwin got a great deal right, and he organized even more material into an internally coherent logic of argument. But he failed to achieve resolution on several important issues (especially when cultural convention clashed with implications of his theory), including some questions of great salience for him. Following his customary frankness, Darwin made no false claims for consistency, and ambiguities remain in his writing. In so doing, he followed the prescription for greatness in two famous statements by celebrated Ameri­cans: “A foolish consistency is the hobgoblin of little minds” (R. W. Emerson, 1841, Self-Reliance).

  Do I contradict myself?

  Very well then, I contradict myself,

  (I am large, I contain multitudes).

  (Walt Whitman, Song of Myself, from Leaves of Grass)

  Darwin's greatest failure of resolution centered on an issue that assumed cardinal importance in Victorian culture — progress (both its definition, and its empirical and theoretical justification). Our current world of nuclear weaponry and global pollution does not rank this issue so centrally, but we have never escaped its allure. Several key figures of the Modern Synthesis devoted books to the subject (Huxley, 1953; Simpson, 1947; Dobzhansky, 1967; Stebbins, 1969), while symposia and volumes still appear with great regularity (Nitecki, 1988; Ruse, 1996; and Gould, 1996a, for a contrary view).

  Darwin's dilemma can be stated easily: The bare-bones mechanics of the [Page 468] theory of natural selection provides no rationale for progress because the the­ory speaks only of adaptation to changing local environments. (The morpho­logical degeneration of a parasite may enhance local adaptation as surely as any intricate biomechanical improvement in a bird's wing.) Moreover, Dar­win regarded the banishment of inherent progress as perhaps his greatest con­ceptual advance over previous evolutionary theories — and he said so, often and forcefully, as in this epistolary comment, previously cited on page 373, to the American progressionist paleontologist Alpheus Hyatt on December 4, 1872: “After long reflection I cannot avoid the conviction that no innate ten­dency to progressive development exists” (in F. Darwin, 1903, vol. 1, p. 344).

  On the other hand, Darwin was not prepared to abandon his culture's cen­tral concern with progress, if only to respect a central metaphor that appealed so irresistibly to most of his contemporaries — that if the history of life em­bodied predictable advance, then imperial expansion and industrial growth might be validated, at least by analogy, as the inherent consummation of Vic­torian desire and destiny, and not merely as an odd and ephemeral bump on the surface of history. And so Darwin penned other statements with equal as­surance, as in this famous comment at the close of the Origin: “As natural se­lection works solely by and for the good of each being, all corporeal and men­tal endowments will tend to progress towards perfection” (1859, p. 489). Both opinions appear prominently and often in Darwin's writing, and they do not jibe.

  This ambivalence on the specific question of progress highlights a broader issue at the center of Darwinism. Amidst the various meanings of Lyell's “uniformitarianism,” one concept has been judged as paramount by many scholars (notably Rudwick, 1969): “non-progressionism” or uniformity of state — the proposition that the earth remains in a dynamic steady-state of constant, pulsating, cyclical change without direction: a strange kind of ahistoricism at the heart of ceaseless motion. Darwin owed a profound intellec­tual debt to Lyell, including far more than the expropriation of a geological stage to support the play of natural selection (see both Chapter 2 and later sections of this chapter). By transfer and analogy, Lyellian uniformity also provided a methodology for the general formulation and application of natu­ral selection itself. Lyell's view of change gave Darwin a framework not only for the obvious features of gradualism, incrementalism, and extrapolationism (as often noted), but also for the less recognized ahistoricism of evolutionary mechanics. The bare bones of natural selection supply no vector for the path­way of life: environments change in their non-directional manner, and organ­isms respond in a continuous dance of local adjustment.

  But the history of life includes some manifestly directional properties — and we have never been satisfied with evolutionary theories that do not take this feature of life into account (see Gould, Gilinsky and German, 1988). (Indeed, the stubbornly vectorial properties of paleontological change eventually led Lyell to surrender this key aspect of uniformity in later editions of the Princi­ples of Geology — the most significant alteration of his intellectual ontogeny; see Gould, 1987b.) Darwin felt that natural selection could not be accepted [Page 469] as a thoroughly sufficient theory of evolution unless this mechanism could also explain evidences of pattern and vector in life's history. But how could Darwin meet such a requirement if natural selection — as a central attribute of its radical character and not a peripheral aspect easily withdrawn or compro­mised — had been devised as a biological analog for Lyell's uniformity of state, or non-directionalism?

  I have just epitomized Darwin's dilemma in its most abstract form. In the immediate practice of his century, one prominent example consumed nearly all discussion of the general subject of vector and pattern — the concept of progress. If Darwin could validate progress by natural selection, then he would solve his dilemma of how to extract directional pattern from an appar­ently ahistorical theory.

  This context of validating a concept of progress in macroevolution estab­lishes an unconventional locus for a discussion — now to follow — on the key Darwinian subject of “struggle” and the nature of competition in general, but I am convinced that this topic finds its best fit at this point within the ba­sic logic of Darwinian argument, and that a failure to recognize this appropri­ate place has led many evolutionists to underappreciate the theoretical sig­nificance of much that geology and paleontology have provided of late towards the reformulation of our subject — particularly
the significance of mass extinction as an agent of change, and the central role of vectorial pat­terns as a subject in itself. (To readers who wondered why I treated struggle so cursorily in Chapter 2 on the essentials of Darwinian argument, I apolo­gize for any puzzlement, while asserting that the subject — meriting all its tra­ditional importance — belongs here.)

  Evolutionary biologists should never lose sight of a cardinal principle link­ing history and function — that historical origin and immediate utility repre­sent independent subjects with no necessary connection (see Chapter 11 for an extended discussion of this principle). Struggle and competition entered the ontogeny of Darwin's thought for a variety of reasons related to Malthus, the necessary hecatomb for powering natural selection, views on the pleni­tude of nature, etc. Struggle also serves many functions in the logic of Dar­win's completed theory. But I believe that one role may be designated as para­mount. Darwin used his distinctive views on struggle to validate the concept of progress as a cardinal vector in the history of life. He invoked his own in­terpretation of struggle — in particular, his conviction about the predomi­nance of biotic competition — as an “added” principle to guarantee a pattern of progress that could not be derived, without such an auxiliary, from natural selection in its most abstract and generalized form.

  But logics of argument form webs, and no benefit accrues without a price, or at least a set of implications. The dominance of biotic competition could validate progress — and thus, in a vital sense, “complete” the Darwinian sys­tem. But the adoption of such an argument required that a premise be im­ported from a field external to the biological logic of selection — and such increases in the logical complexity of theories also court danger. In this partic­ular case, the domination of biotic competition as a patterning agent requires [Page 470] that the earth's geological history proceed in a particular way: for the stage of environmental change must permit the Darwinian play to operate (and domi­nate) in our real world. Even the most logical and brilliant theory can do no explanatory work if surrounding conditions never permit its results to emerge. (The expansion of H2O upon freezing may be both true and ab­stractly important, but irrelevant on a hot planet that has never experienced a temperature approaching 0°C.)

  Darwin himself may not have felt the press or worry of this added commitment to a Lyellian earth, for his belief in such a world had deep roots, well an­tedating his formulation of natural selection (see his first three geological books on coral reefs, volcanic islands, and the geology of South America — 1842, 1844, and 1846). Still, the conceptual constraint of requiring an exter­nal license for an internally consistent mechanism has operated as a distinc­tive and problematical claim throughout the history of Darwinism. I shall, in this chapter, first explicate Darwin's argument about biotic competition and progress, then discuss the required geological license more directly, summa­rize the strengths and character of the unfairly maligned catastrophist alter­native, and suggest how an alteration of the geological stage might modify or expand the tenets of Darwinism.

  THE PREDOMINANCE OF BIOTIC COMPETITION

  AND ITS SEQUELAE

  We all know that the most vulgar misinterpretation of Darwin, often willfully made for martial ends, holds that “survival of the fittest” mandates the subju­gation and extermination of people and nations considered inferior. We also know the conventional and proper response to this harmful distortion: Dar­win conceived “struggle” as a metaphorical concept defined in terms of re­productive success, not bloody battle. We can all cite the famous and stan­dard quotation: “I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on an­other, and including (which is more important) not only the life of the indi­vidual, but success in leaving progeny. Two canine animals in a time of dearth may be truly said to struggle with each other, which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent upon the moisture” (1859, p. 62).

  Still, the link of struggle with overt battle does play a crucial role in Dar­win's thought. He did include both biotic competition (the domain of overt battle) and prevalence in difficult environments (the plant at the edge of a desert) within his larger concept of struggle. And he did regard all forms of biotic competition, including symbiosis and symbolic posturing for success in mating — not only combat leading to death or injury — as modes of struggle. Nonetheless, by strongly emphasizing biotic over abiotic competition, and by stressing examples leading to the death of losers, Darwin did favor the close analogs of battle. Thus, his friend and supporter T. H. Huxley frequently referred [Page 471] to natural selection as the “gladiatorial theory” of existence and, in his famous essay on ethics and evolution (1893), urged human beings, as a pri­mary ethical precept, to determine nature's ways and then act in an opposite manner. (Gladiators, by the way, and to make Huxley's etymological point, are not happy or grateful people, but warriors who fight to the death with a gladius, or sword in Latin.)

  Darwin's decided choice in advocating a predominant relative frequency for biotic competition as a mode of struggle forms the crucial link in a chain of argument that stretches back to basic beliefs about the fullness of nature and points forward to a rationale for progress and the need for a uniformitarian geological stage. Consider a sequence of five consecutive, but interre­lated subjects:

  The rule of biotic competition

  Prince Peter Kropotkin, the charming Russian anarchist who spent 30 years in English exile, has generally been viewed as idiosyncratic and politically motivated in his famous attack on Darwinian competition, and his advocacy of cooperation as the norm of nature — Mutual Aid (1902). In fact, Kropot­kin, who was well trained in biology, spoke for a Russian consensus in argu­ing that density-independent regulation by occasional, but severe, environ­mental stress will tend to encourage intraspecific cooperation as a mode of natural selection (Todes, 1988; Gould, 1991b). The harsh environments of the vast Russian steppes and tundras often elicited such a generalized belief; Kropotkin and colleagues had observed well in a local context, but had erred in overgeneralization. But Darwin and Wallace, schooled in the more stable and diversely populated tropics, may have made an equally parochial error in advocating such a dominant role for biotic struggle over limited resources in crowded space (Todes, 1988).

  The shaping of diversity and the powering of natural selection by biotic competition — and not primarily by simple selective response to changing physical conditions — forms a central and recurring argument in the Origin. Three primary themes record its sway:

  The necessary prerequisite of plenitude. If populations gen­erally stand at their carrying capacity, with numbers not fluctuating greatly, then biotic competition must dominate, for no group can increase except at the expense of others (while Kropotkin's underinhabited world can support more of any population if, by mutual aid, their members can counteract envi­ronmental stress). Darwin strongly subscribed to this version of the ancient principle of plenitude (see p. 229), arguing from his favored Malthusian base that a population's geometric capacity for growth guarantees the geologically instantaneous achievement of optimal numbers: “From the high geometrical powers of increase of all organic beings, each area is already fully stocked with inhabitants” (1859, p. 109).

  Metaphors of competition. Since Darwin used metaphor so effec­tively, we can often infer his primary commitments from his choice of images. Darwin, as noted before, does cast a broad net in spreading “struggle” across [Page 472] biotic and abiotic realms — but war and conquest, combat and death, provide the principal examples of competition throughout the Origin. Why else did Tennyson's earlier line from In Memoriam (1850) — “nature red in tooth and claw” — become the canonical characterization of Darwin's world (see Gould, 1992a)? We may not know the particular reasons for success, but victory and battle set the appropriate context: �
�Probably in no one case could we pre­cisely say why one species has been victorious over another in the great battle of life” (Darwin, 1859, p. 76). Two species, previously isolated and meeting for the first time “are maiden knights who have not fought with each other the great battle for life or death. But, whenever . . . they meet, and come into competition, if one has the slightest advantage over the other, that other will decrease in numbers or be quite swept away” (Natural Selection, 1856-1858, 1975 edition, edited by Stauffer, p. 227). Calmness and cooperation may seem to hold sway, but lift the veil and observe the struggles to death in this vale of tears: “We behold the face of nature bright with gladness, we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings, are destroyed by birds and beasts of prey” (1859, p. 62).

  Explicit statements of relative frequency. Darwin often contrasts the relative strengths of relationships among organisms vs. response to physical conditions. In each case, he stresses the greater importance of bi­otic competition. Migration, for example, will affect species more by forcing them into competition with other creatures than by exposing them to new physical environments: “These principles come into play only by bringing or­ganisms into new relations with each other, and in a lesser degree with the surrounding physical conditions” (p. 351). Speaking of movement to oceanic islands, Darwin notes the “deeply-seated error of considering the physical conditions of a country as the most important for its inhabitants; whereas it cannot, I think, be disputed that the nature of the other inhabitants, with which each has to compete, is at least as important, and generally a far more important element of success” (p. 400). And, in his baldest statement, Dar­win asserts (p. 477) “the relation of organism to organism is the most important of all relations.”