The Structure of Evolutionary Theory

by Stephen Jay Gould

  We may best illustrate the depth of feeling (and the perceived extent of Goldschmidt's apostasy) by examining the review of Material Basis written for Science by Th. Dobzhansky (1940), whose own Genetics and the Origin of Species had codified the developing Synthesis three years earlier. The rhe­torical strategy of this review embodies the general reaction of the emerging Neo-Darwinian consensus. Dobzhansky grants warmest praise to Gold­schmidt's persona and to the sweep of his effort. He begins by stating: “This book contains the only basically new theory of organic transformation pro­pounded during the current century” (1940, p. 356) — a peculiar statement, given the former popularity of de Vriesian saltationism (although Dobzhan­sky may have viewed de Vries's Mutation Theory, not formally printed until 1901, as a late 19th century formulation, especially since de Vries had pub­lished his major empirical work on Oenothera in the 1880's and 1890's). For Dobzhansky, only three serious theories of evolutionary mechanics precede Goldschmidt's book — Lamarckism, which “has become obsolete owing to its basic assumption having fallen short of experimental verification” (p. 356); autogenesis (orthogenesis), dismissed as “in conflict with the principle of causality in vogue in the materialistically-minded modern science” (loc. cit.); and Darwinism, which Dobzhansky accepts, and which “underwent great changes because of the forward strides of genetics, but the unbroken continuity [Page 455] of ideas between the 'neo-Darwinism' and Darwin's original theory is evi­dent.” Goldschmidt's book now “connotes an at least temporary end of the undivided reign of neo-Darwinian theories” (loc. cit.).

  Dobzhansky covered his review in a patina of judiciousness, even of approbation. He also presents a fair and clear epitome of Goldschmidt's major points. Dobzhansky refers to Goldschmidt's theory as “brilliantly developed and masterfully presented” (p. 357), and he adds: “Goldschmidt's keenly crit­ical analysis has emphasized the weaknesses and deficiencies of the neo-Dar­winian conception of evolution, which are numerous, as even partisans ought to have the courage to admit” (p. 358).

  But, in the deeper theme and purpose of his review, Dobzhansky's rejection could not have been more total or dismissive (much as he advocates a close reading and study of Goldschmidt's book). First of all, he does not count Goldschmidt's ideas as an evolutionary theory at all, as expressed in the title of Dobzhansky's review: “Catastrophism versus evolutionism.” The first sen­tence, as quoted above, presents Goldschmidt's theory as the first new view of “organic transformation,” not of evolution — words that Dobzhansky chose very carefully and purposefully. He then explains: “Goldschmidt not only rel­egates natural selection to a place of relative unimportance, but in effect re­jects evolution beyond the narrow confines in which it has been admitted to exist by Linnaeus and many creationists. His theory belongs to the realm of catastrophism, not to that of evolutionism.”

  Recalling the stereotypical cry of the stadium vendor — “you can't tell the players without a scorecard” — later scholars often need a historical primer of definitions to identify certain claims properly. Dobzhansky refers here to Lyell's rhetorical strategy for specifying the requirements of a scientific geol­ogy. A truly scientific theory based on verae causae (true causes), Lyell tells us, must embrace the uniformitarian postulate that small-scale changes, observ­able on our current earth, can produce, by gradual accumulation through geological time, all the grand events of our planet's history. Evolution, for Dobzhansky, defines all theories of biological change set within this proper uniformitarian mode. The catastrophic alternative — that occasional parox­ysms sweep the earth to produce most important change, whereas the daily accumulation of tiny, observable alterations can lead to nothing substantial — represents a retreat to the bad old days of useless speculation and theological influence. Goldschmidt's saltational theory of the “hopeful monster” falls into this basically unscientific mode. As Lyell wrote in his magisterial prose (1833, p. 6): “Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity ... We see the ancient spirit of specula­tion revived, and a desire manifested to cut, rather than patiently to untie, the Gordian knot.” Therefore, by placing Goldschmidt's book within the catastrophist tradition, Dobzhansky almost denies any scientific status to the theory at all.

  Dobzhansky then reinforces his dismissal by declining even to present any counterarguments: “It is impossible to attempt here a critique of Gold­schmidt's theory, for this would require a book approximately the same size [Page 456] as his own” (p. 358 — indeed, Mayr would soon write such a rebuttal). But Dobzhansky's demurral does not prevent him from trying to annihilate Goldschmidt with the unkindest cut of all — an explicit removal of scientific status: “But in the reviewer's opinion the simplicity of Goldschmidt's theory is that of a belief in miracles” (p. 358).

  No one can deny that Goldschmidt's theory merits historical attention for its palpable and extensive influence, at least upon the psyches of his major op­ponents. But we also need to assess whether anything in Goldschmidt's theory merits our respect and study today. We must therefore clarify a primary issue that Goldschmidt himself unfortunately plunged into deep confusion: how shall we characterize the genetic source of saltations that make new species? Beginning in the 1930's, and extending with increasing scope, unconventionality, and self-assurance to his death, Goldschmidt developed an idiosyncratic concept of genetics that eventually sought to refute the “particulate” or “cor­puscular” gene entirely (see the culmination of this development in Gold­schmidt's last and least cogent book — Theoretical Genetics, 1955. A compar­ison between Goldschmidt's “holistic” view and Bateson's unwillingness to abandon his “vibrational” theory of heredity would provide an interesting subject of research. I suspect that more than mere coincidence must inhere in the observation that Bateson and Goldschmidt — the most thoroughly non-Darwinian thinkers among important 20th century evolutionists, particularly as expressed in their full and coordinated support for the channeling and the facet-flipping themes of Galton's polyhedron — both insisted upon a holistic concept of genetic material).

  In short, Goldschmidt finally concluded that the underlying basis for all mutational change must be sought in alterations of chromosomal patterns. If inversions, translocations, and other chromosomal changes can exert such a marked effect upon phenotypes in the absence of alteration within supposed genes, why should genes exist at all as discrete and bounded entities? Perhaps all genetic changes arise as alterations in pattern, with mappable, so-called micromutations as modifications of minimal spatial extent and phenotypic effect. (Goldschmidt, of course, did not deny the methodology of locating and mapping “genes” on chromosomes. He merely considered these loci as operationally definable spots on an indivisible chromosome. Order must be conserved for normal development. The “mutations” of conventional ter­minology must represent disruptions of this standard order, not material changes within discrete entities.) Eventually, Goldschmidt even regarded indi­vidual chromosomes as mere segments of a more comprehensive, holistically acting, system. As he touted this concept with increasing vigor and assurance, even after Watson and Crick's resolution of the structure of DNA in 1953, Goldschmidt became more and more marginalized within his field.

  This idiosyncratic view of genetics bears an obvious relationship to Goldschmidt's saltational concept. If all genetic change can be rendered as alteration of pattern within a single integrated system, then some changes must be great enough in scope to reorient the entire program of development (while others, with only local effect, correspond to micromutations of standard interpretations). [Page 457] Goldschmidt called these pervasive changes “systemic muta­tions,” and he identified them as the underlying source of saltational events that produce new species by transcending the ineffective Darwinian diversi­fication of races:

  For a long time I have been convinced that macroevolution must proceed by a different genetic method ... A pattern change in the chromosomes, completely independent of gene mutation
s, nay, even of the concept of the gene, will furnish this new method of macroevolution . . . So-called gene mutation and recombination within an interbreeding population may lead to a kaleidoscopic diversification within the species, which may find expression in the production of subspecific categories . . . The change from species to species is not a change involving more and more additional atomistic changes, but a complete change of the primary pattern or reaction system into a new one, which afterwards may again pro­duce intraspecific variation by micromutation. One might call this differ­ent type of genetic change a systemic mutation . . . Whatever genes or gene mutations might be, they do not enter this picture at all. Only the arrangement of the serial chemical constituents of the chromosome into a new, spatially different order, i.e., a new chromosomal pattern, is in­volved (1940, pp. 205-206).

  This bold statement highlights the key issue surrounding Goldschmidt's role in current reformulations of evolutionary theory. Goldschmidt clearly ties his phenotypic concept of the “hopeful monster” to his genetic hypothe­sis of “systemic mutation” as a cause. If these two notions are indissolubly linked, and if the hopeful monster can only be conceived as a phenotypic manifestation of this deeply fallacious genetic theory, then we may dismiss this colorful term as a historical curiosity. I place Goldschmidt's denial of cor­puscular genes, and his attempt to construct a holistic genetics based upon position effects in a fully integrated interchromosomal system, into the inter­esting category of major ideas that we may honor as “gloriously wrong.” Goldschmidt made a grand, not a paltry, error — for his system proposes an entirely different way of knowing, with intellectual and scientific ramifica­tions at broadest scale. But this generous breadth of vision doesn't make Goldschmidt's genetic system any less wrong, and the obvious argument re­mains: If hopeful monsters and systemic mutations only represent two aspects of the same phenomenon, then we must place the unitary concept aside, how­ever gently and with sympathetic interest.

  But even a cursory investigation of Goldschmidt's career, and a first-pass analysis of his writings, reveals a separate, older and more important theme behind the concept of the hopeful monster. Goldschmidt sets most of his macroevolutionary discussions in the context of developmental systems and their ontogenies, not of idiosyncratic genetics and their operation. The confu­sions and conflations within The Material Basis of Evolution remain both palpable and frustrating — and must be regarded as Goldschmidt's own doing (and undoing). In this book, he sometimes speaks of systemic mutations as [Page 458] causes of macroevolution — alterations, by chromosomal repatterning, of en­tire genetic systems. But, more often, he discusses macroevolutionary change as a consequence of alterations in developmental ontogeny. His language then becomes dramatically different. Goldschmidt now refers to the genetic basis of large, species-forming phenotypic changes as “mutations” — and he now speaks of conventional alterations at specific sites, not of holistic repatternings. He often describes these mutational changes as “small,” and he ar­gues for far-reaching consequences because genes affect rates of development, and small changes occurring early in growth can trigger cascading results throughout ontogeny. “A single mutational step affecting the right process at the right moment can accomplish everything provided that it is able to set in motion the ever-present potentialities of embryonic regulation” (1940, p. 297). These developmental themes, of course, would be regarded as inter­esting and acceptable to orthodox synthesists (however underemphasized within the traditions of this theory). “The physiological balanced system of development is such that in many cases a single upset leads automatically to a whole series of consecutive changes of development in which the ability for embryonic regulation, as well as purely mechanical and topographical mo­ments, come into play; there is in addition the shift in proper timing of inte­grating processes. If the result is not, as it frequently is, a monstrosity incapa­ble of completing development or surviving, a completely new anatomical construction may emerge in one step from such a change” (1940, p. 486).

  How then shall the hopeful monster be defined: the product of an illusory systemic mutation (and therefore a chimaera to be set aside), or as the result of a small genetic change that, by working early in ontogeny, produces a sub­stantial final effect (and therefore an acceptable idea to stretch the Neo-Darwinian envelope)?

  This confusion epitomizes the key issue for evaluating Goldschmidt's book, since the importance of his macroevolutionary ideas depends upon a resolu­tion. Many readers have noted and commented upon this frustration, and Goldschmidt himself remarked (1955, quoted in Frazzetta, 1975, p. 116): “I have been reproached for not having made clear in my book The Material Ba­sis of Evolution whether I was speaking of systemic mutation (scrambling of the chromosomal pattern) or of ordinary mutations of a macroevolutionary type, and of being confused myself on what I meant.”

  In one sense, of course, any resolution based on Goldschmidt's own intellectual ontogeny must admit a genuine incoherence, even a contradiction, between the different parts of his book. After all, systemic mutations differ markedly from small genetic changes that cascade to large effect by acting early in ontogeny — and Goldschmidt clearly grants each phenomenon, in dif­ferent passages, the dominant role in macroevolutionary change! But I think that several persuasive arguments can be made, including the existence of a genuine literary “smoking gun,” for regarding the developmental theme as more important, both in Goldschmidt's career and in his 1940 book (even though systemic mutation, as a much more radical concept — albeit ultimately [Page 459] false and detrimental to his influence — became the chief obsession of Goldschmidt's old age).

  1. Material Basis grants the developmental theme a clear prominence in both place and space. In his introductory pages, Goldschmidt complains that evolutionary thought suffers by disregarding a vital subject: “There is, finally, another field which has been neglected almost completely in evolutionary discussions; namely, experimental embryology. The material of evolution con­sists of hereditary changes of the organism. Any such change, however, means a definite change in the development of the organism” (pp. 5-6). “A change in the hereditary type can occur only within the possibilities and limitations set by the normal process of control of development” (p. 1).

  The macroevolutionary half of the book — the search for the “other evolutionary method” behind the origin of species — cobbles two strikingly different discussions together: the first (pp. 184-250) on systemic mutation and the non-existence of the “corpuscular gene”; and the second (pp. 250-396) on constraints and opportunities of developmental systems, and the potential macroevolutionary consequences of mutations affecting early development. Goldschmidt strongly emphasized the second discussion (at more than twice the length devoted to the first theme). Moreover, he situated his entire treat­ment of hopeful monsters (pp. 390-393) within the developmental section. In the opening paragraph on hopeful monsters, Goldschmidt lists his favorite potential examples — concrescence of tail vertebrae to produce a fanlike ar­rangement of feathers in ancestral birds, the passage of both eyes to one side of the head in flatfishes, and an achondroplastic bow-legged dog that ranks as a mere monster until humans need to extract badgers from dens and therefore breed dachshunds. Goldschmidt interprets these examples entirely in terms of small mutations affecting early development. He states, following the citation of dachshunds (p. 391): “Here, then, we have another example of evolution in single large steps on the basis of shifts in embryonic processes produced by one mutation . . . This basis is furnished by the existence of mutants produc­ing monstrosities of the required type and the knowledge of embryonic deter­mination, which permits a small rate change in early embryonic processes to produce a large effect embodying considerable parts of the organism.”

  2. The developmental theme pervaded Goldschmidt's career, in both dura­tion of work and centrality of focus. I mentioned above (p. 453) that Gold­schmidt centered his empirical studies upon the gypsy moth, Lymantri
a dispar. His voluminous research on the genetics of geographic variation, pub­lished under the collective title Untersuchungen zur Genetik der geographischen Variation, convinced him that diversification within species, though Darwinian and adaptive, did not lead to the origin of new species. But Gold­schmidt pursued a second line of work on Lymantria for more than 20 years and through equally voluminous publication — studies on sexual determina­tion and intersexuality (culminating in a long series of papers collectively titled, Untersuchungen iiber Intersexualitat).

  In these developmental studies, Goldschmidt recognized normal sexuality [Page 460] as a quantitative phenomenon produced by a balance of male and female sex determiners. He produced a series of graded intersexes by altering these bal­ances experimentally. At a time (between 1910 and 1920) when the great ma­jority of geneticists focused their work upon basic principles of transmission, Goldschmidt had already begun to study gene function and development — in order to establish a profession that he called “physiological genetics.” He rec­ognized that genes work by controlling the rates of chemical processes. Nor­mal development requires a proper balance and definite timing of substances; evolutionary change occurs by alteration in the timing of development. Gold­schmidt initiated and extended the concept of “rate genes,” and the germ of the hopeful monster clearly lies within this crucial concept of his career.