The Structure of Evolutionary Theory

by Stephen Jay Gould

  Geoffroy's attempted comparisons posed two major challenges to his own “law of connections” for establishing homology: how can inside and outside become reversed if topology be inviolate; and how can arthropods, with their ventral nerve tracts, be brought into structural harmony with the dorsal nerve cord of vertebrates? Geoffroy proposed an ingenious explanation for the me­tastasis of inside and outside: He argued that hard parts (and other organs) develop as deposits or exudates on the outside of vessels. In vertebrates, the dorsal nerve cord secretes the vertebrae around itself, while other organs emerge as exudates around vessels of the circulatory system. But insects lack a heart, making their circulatory system too weak to build organs. Therefore, only the nervous system can carry material for the deposition of hard parts — and all other organs must form within the resulting outer set of rings.

  The inversion of orientation did not require such an elaborate rationale, but only a repositioning of viewpoint. Geoffroy regarded “top” and “bot­tom” as subjective terms of a secondary and derivative functionalism. (Geoffroy never intended his homology of vertebrates and inverted arthro­pods as an evolutionary claim for the origin of vertebrates from an arthropod that literally turned over onto its back. For Geoffroy, the two orientations represented ecological alternatives for a common design.) The primary topol­ogy of formalism puts little store by the derivative ecology and function that leads the same side of an invariant organization to turn towards the sun in some groups, and towards the ground in others.

  This solution is not, by any means, problem-free, for such changes of topology must also be rationalized. In particular, and as a major stumbling-block [Page 306] (especially for later, evolutionary versions in the “worm that turned” theory of vertebrate origins), the mouth lies below the brain and spinal cord in vertebrates, but above the nerve cords in arthropods, with the esophagus piercing through the cords. Turn an insect over, and the mouth should lie on top, above the brain. Geoffroy and later supporters of this homology gener­ally argued that the old arthropod mouth and nerve-piercing esophagus sim­ply closed, while the digestive tube formed an entirely new ventral “mouth” (therefore not homologous with the arthropod orifice). In any case, and with an almost wondrous and partly humorous irony as I shall show in Chapter 10, Geoffroy's fundamental homology has been validated (in modern guise) after more than a century of calumny. The genetic determinants of dorsoventral patterning may well be homologous but reversed in expression in arthro­pods and vertebrates (see pp. 1117–1123).

  If Geoffroy belittled Cuvier's functionalism in his argument about orienta­tion, he also attacked the deeper postulate of adaptational primacy by argu­ing, once again, that the archetypal vertebra comes first, with any use of the resulting structures developing only later as a consequence. Why, he asks, do arthropods use their “ribs” for locomotion? And he answers with the old cliché about mountain climbing — because they are there. Geoffroy wrote in 1820 (quoted in Russell, 1916, p. 77): “From the circumstance that the verte­bra is external, it results that the ribs must be so too; and, as it is impossible that organs of such a size can remain passive and absolutely functionless, these great arms, hanging there continually at the disposition of the animal, are pressed into the service of progression, and become its efficient instru­ments.”

  Cuvier may have been offended by the arthropod connection, but he was too smart a rhetorician, and too much a figure of the establishment, to be drawn into the limelight of public debate, thus giving even more publicity to Geoffroy's apostasy. Geoffroy goaded him throughout the 1820's, but with no public response. Finally, the dam burst in 1830. Meyranx and Laurencet, two young provincial naturalists with an eye on advancement, presented a monograph, “Some considerations on the organization of mollusks,” to the Academie des sciences — the standard path for career building at the time. They suggested that the anatomy of a squid might be homologized with a ver­tebrate bent back upon itself at the middle of the vertebral column, so that the buttocks and base of the spine lined up with the nape of the neck.

  Their original paper has been lost, and we do not know how far they meant to carry the comparison, or how much they had intended to inject themselves into the formalist-functionalist controversy. But we do know that Geoffroy, appointed as one of two commissioners to prepare a public report for the Academie, rejoiced at this entering wedge for a second imperialistic raid upon Cuvier's embranchements. The inclusion of arthropods had once seemed rad­ical enough, but if mollusks could also be brought under the vertebral arche­type, then three of four phyla would be reduced to common design, and a final absorption of the Radiata could not lag far behind. The dream of total unification now seemed within Geoffroy's grasp. [Page 307]

  Therefore, at the weekly, Monday afternoon meeting of February 15, 1830, Geoffroy presented an enthusiastic endorsement of Meyranx and Laurencet's work, perhaps extending their conclusions far beyond their own intents and desires. And Cuvier finally reached his breaking point.

  On February 22, Cuvier appeared, colored charts in hand, to demolish the proposed homology of mollusk and vertebrate. He showed, with devastating effect, that although some organs may look similar and bear the same name, they occupy entirely different topological positions in the two phyla and therefore cannot be homologized by Geoffroy's own criterion of connection. Moreover the anatomy of cephalopods features several organs not found in vertebrates at all. Strongly attacking Geoffroy and his pretensions, Cuvier stated (in Geoffroy, 1830, p. 243):

  One of our learned colleagues, Monsieur Geoffroy Saint-Hilaire avidly seized upon this new view and announced that it completely refuted all that I had said on the distance that separates mollusks and verte­brates. Going much further than the authors of the memoir [Meyranx and Laurencet], he concluded that, up to now, zoology had had no solid base, that it had been an edifice constructed upon sand, and that the only true basis, henceforth indestructible, shall be a certain principle that he calls unity of composition [unite de composition], and which, he assures us, will have a universal application.

  Following this flourish of controlled contempt, Cuvier presented his spe­cific rebuttal (in Geoffroy, 1830, p. 257): “Cephalopods have several organs in common with vertebrates, and fulfilling similar functions; but the organs are differently arranged in mollusks, often constructed in a different manner, and accompanied by several other organs that vertebrates do not possess.”

  Poor Meyranx and Laurencet. They became the ultimate victims of numer­ous clichés, hackneyed by virtue of their fundamental truth — bit off more than they could chew, sacrificial lambs, caught in the middle, between Scylla and Charybdis, a rock and a hard place. The two young men disappeared, forthwith and permanently, both from immediate view, and from later his­tory. Of poor Laurencet, we do not even know his first name (official reports, in those days, spoke only of M. — for Monsieur — so-and-so). Of the equally wretched Meyranx, we know only his attempt to rend his garments before the powerful Cuvier. He wrote, in an abject letter to Cuvier (quoted in Appel, 1987, p. 147): “I cannot find words to express how devastated I am that our Memoir has given rise to disputes. We could scarcely believe that anyone could draw such exaggerated consequences from a single, simple consider­ation on the organization of mollusks.” He then added that the memoir con­tained nothing “which contradicts the admirable work that you have written and that we regard as the best guide in this matter.”

  Cuvier, having demolished a specific argument about mollusks, and grasp­ing the deeper issue with his usual clarity, set the groundwork for expanding the debate by defending his functionalist view against the true subject of Geoffroy's primary concern — the defense and hegemony of formalist morphology. [Page 308] Cuvier stated (in Geoffroy, 1830, pp. 248-249), belittling the idea of unity of type: “It [unity of type] is only a principle subordinate to another that is much more important and much more fecund — that of the conditions of existence, of the fitting of parts and their coordination for the role that the ani
mal must play in nature. This is the true philosophical principle, from which flows the possibility of certain resemblances, and the impossibility of others; this is the rational principle from which one may deduce that of anal­ogies [homologies in modern usage] of plan and composition.”

  With Meyranx, Laurencet and mollusks forgotten (to Cuvier's satisfaction and Geoffroy's relief), the debate moved on to greater generalities of formal­ism vs. functionalism. Geoffroy replied briefly on February 22, and then, on March 1, presented a general defense of his theorie des analogues (homo­logies), illustrated primarily with his old favorite example of hyoid bones in fishes and tetrapods. On March 8, Geoffroy had fallen ill and Cuvier refused to deliver his rebuttal in his colleague's absence. The large crowd, lured by the promised fireworks more than the putative content, dispersed in disap­pointment. Cuvier replied in kind by failing to attend the following week; tit for tat. The debate finally resumed on March 22, with Cuvier's rebuttal of Geoffroy's claims for hyoid homologies. Geoffroy defended himself on March 29, but he had clearly tired of the affair, for he stated, with more than a whiff of disingenuous disengagement, that “a meeting of the disciples of the Portico” had regretfully turned into theater — “a pit applauding the outra­geous comedies of Aristophanes” (quoted in Appel, 1987, pp. 154-155). Cuvier replied one last time on April 5, but Geoffroy ended the public debate by announcing that he would not respond. Cuvier surely enjoyed advantages as a brilliant debater and consummate politician, but we must not consider Geoffroy either devoid of wiliness, or willing to surrender. He merely shifted ground to the more comfortable medium of print. By April 15, in a fit of zeal and celerity as impressive as anything achieved with our current technology of instant books, Geoffroy had sent to the printers the text of his Principes de philosophic zoologique, containing all papers and commentary presented by Cuvier and himself during the public debate. (Several years ago, I had the good fortune to purchase Cuvier's own copy of this work. The book bears Cuvier's library stamp (Fig. 4-11), but I find no sign, in marginalia or any other indication of use, that the great man ever consulted the volume!)

  Intellectual debates of such grand scale and diverse content can never be won or lost in the unambiguous fashion of more worldly events, as when Joe Louis knocked out Max Schmeling. Most biological texts (Russell, 1916, for example) proclaim Cuvier the victor — surely a fair judgment for the narrow, initiating topic of molluscan homologies. But the debate quickly moved from this immediate instigation to the broadest question of formalism vs. function­alism — an issue that cannot be resolved as total victory or defeat. Moreover, the debate embodied a hundred subtexts in sociology, philosophy, and poli­tics — open vs. closed meetings of the Academie, facts vs. theory in science, elites vs. populism in research — and all these swirling, largely orthogonal themes could not fall into a single pattern of victory for one side. [Page 309]

  Furthermore, and in a curious sense, the debate didn't seem so tumultuous, fierce, or epochal at the moment of its actual unfolding — six meetings, two misses, and an abrupt, unfinished ending. This incident became central to the later history of biology largely through machinations and unplanned conse­quences of its aftermath, and primarily because a mixture of good luck and a special kind of insight allowed the dreamer Geoffroy to recoup everything he had lost in immediate debate to the magisterial Cuvier, and to attain some sort of victory in retrospect, or at least a “draw” with great advantages.

  On the ledger of luck, Geoffroy gained history's greatest and most conventional form of advantage when Cuvier died in 1832, thus awarding Geoffroy 12 additional years to reconstruct the incident, unopposed and in his fashion (a kind of poetic justice in this case, since Cuvier had so adroitly used the same power with such effect — as in his infamous eloge of Lamarck, see pp. 170–173). Secondly, Geoffroy obtained the finest free publicity conceiv­able when Europe's greatest literary figure, the aged Goethe, expressed such

  4-11. A remarkable artifact in the history of evolutionary biology! This is the title page of Cuvier's personal copy — a “gift” from Geoffroy — of the volume that Geoffroy so quickly edited and published after their debate of 1830 at the Academy of Sciences. (Author's collection.) I can find no evidence that Cuvier, after placing his library stamp upon this volume, ever read a word of the text. Following Cuvier's death, this book became the property of the Library of the Museum d'Histoire naturelle, which later sold it as a duplicate.)

  [Page 310]

  lively interest in the debate and wrote two articles on the subject, including the very last piece before his death (Goethe, 1832). Although Goethe declared no victor, his basic sympathy lay with Geoffroy — a kindred soul who de­fended poetic insight against pure empiricism, and who had, in a real sense that inspired their deepest intellectual bond, completed for animals (with the archetypal vertebra) the program that Goethe had begun so brilliantly for plants (and their archetypal leaf).

  The debate of Geoffroy and Cuvier unfolded during one of the most impor­tant and tumultuous events of 19th century French history — the revolution of 1830. This coincidence prompted the most famous anecdote of the entire epi­sode — a tale that documents the extent of Goethe's involvement. Goethe's friend Frederic Soret recalled:

  The news of the Revolution ... reached Weimar today, and set everyone in a commotion. I went in the course of the afternoon to Goethe's. “Now,” he exclaimed as I entered, “what do you think of this great event? The volcano has come to an eruption; everything is in flames, and we no longer have a transaction behind closed doors!” “A frightful story,” I replied. “But what else could be expected under such notorious circumstances, and with such a ministry, than that matters would end with the expulsion of the royal family?” “We do not appear to under­stand each other, my good friend,” replied Goethe. “I am not speaking of those people at all, but of something entirely different. I am speaking of the contest, of the highest importance for science, between Cuvier and Geoffroy Saint-Hilaire, which has come to an open rupture in the Acad­emy” (quoted in Appel, 1987, p. 1).

  In his first article (1831, p. 179), Goethe conjured up the scene of debate: “In this sanctuary of science . . . where all is order and decorum, where one encounters people of high culture, where one responds with moderation ... lively debate has broken out, debate which appears to lead only to personal dissention, but which, viewed from a higher perspective, has more value and more future worth.” He then epitomized the differences between the protago­nists in both method and theory (1831, p. 180): “Cuvier presents himself as having an indefatigable zeal for distinction and description . . . Geoffroy de­votes himself to the hidden affinities of creatures . . . The totality is always present in an interior sense, from which follows the conviction that the par­ticular can arise from the totality.”

  Goethe also recognized the link between a commitment to formalist constraints and channels, and a reluctance to explain morphology by utility and adaptation — for he had promoted the same correlation in his own work on plants. Presenting the most essential aspect of Geoffroy's methodology, Goethe writes (1832, p. 62): “It is necessary to cite, as most important, his having shown the uselessness of explanations in terms of final causes.”

  Geoffroy surely enjoyed good fortune in Cuvier's death and Goethe's inter­est, but he also actively campaigned in an unconventional yet strikingly effec­tive manner, for elevating the importance of the debate and rewriting its story [Page 311] to his advantage. As stated above, his book of documents went to the printers just 10 days after the debate ended. Although he did not importune Goethe directly, he surely took full advantage of this fortuitous involvement (see Fig. 4-8 for some private evidence). Speaking before the Academie later in 1830, Geoffroy noted Goethe's favorable commentary on his “instant” book, refer­ring to the great poet as “the first authority of Germany . . . the celebrated Goethe . . . who has just accorded my work the greatest honor that a French book can receive” (quoted in Appel, 1987, pp. 166-167).
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br />   Taking a cue from Goethe's clout, Geoffroy actively recruited support from literary leaders in France. Balzac dedicated Fere Goriot, perhaps his most fa­mous novel, “to the great and illustrious Geoffroy Saint-Hilaire as a tribute of admiration for his labors and his genius.” The avantpropos to Balzac's La comedie humaine (1842) contains the following description of Geoffroy's sys­tem:

  There is only one animal. The Creator has used only a single pattern for all organized beings. The animal is a principle, which takes its exter­nal form, or, to be more exact, the differences in its form, from the mi­lieus in which it is obliged to develop. Zoological species are the result of these differences. The proclamation and defense of this system, which is, moreover, in harmony with our ideas of divine power, will be the eternal glory of Geoffroy Saint-Hilaire, the victor over Cuvier in this point of higher science, and whose triumph has been hailed by the last article written by the great Goethe (in Appel, 1987, p. 192).

  Balzac then used Geoffroy's centerpiece, in a timely and fascinating way, in this and other novels — arguing that all people partake of a single human es­sence, with individual variation best explained by environmental differences.

  Geoffroy also courted the friendship and publicity of George Sand. Of a meeting with Geoffroy at the Jardin des Plantes in 1836, she wrote: “The old Geoffroy is for his part a rather curious beast, as ugly as the orangutan, as talkative as a magpie, but for all that full of genius” (in Appel, 1987, p. 189). Geoffroy sent Sand several of his publications; she declared herself unable to do them technical justice, but still proclaimed them “broad and magnificent,” throwing Cuvier “to the ground ... for anyone who detests meanness in the arts” (in Appel, 1987, p. 189).