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Natural History
March, 1999

Branching Through a Wormhole.(reclassifying the types of 'worms')

Author/s: Stephen Jay Gould

Lamarck's Ladder Collapses

In 1800 the French zoologist Jean-Baptiste Lamarck changed the science of biology forever by presenting the first public account of his theory of evolution at the Museum d'Histoire Naturelle. More than a half century before Charles Darwin published On the Origin of Species, Lamarck proposed that modern species had descended from common ancestors over immense periods of time. In Part One of this essay, the author discussed Lamarck's original model, which consisted of two vectors--an upward ladder of progression, modified by the lateral pull toward local adaptations. Part Two demonstrates how Lamarck's study of invertebrates eventually compelled him to abandon that system and to arrive, well heft)re Darwin, at the paradigm of a branching bush or tree life--Eds.

PART TWO

V. AN ODYSSEY OF WORMS

I have always considered it odd (and redolent either of arrogance or parochialism) when a small minority divides the world into the two wildly unbalanced categories of itself versus all others and then defines the big category as an absence of the small--as in my grandmother's taxonomy for Homo sapiens: Jews and non-Jews. Yet our conventional classification of animals follows the same strategy by drawing a basic distinction between vertebrates and invertebrates--when only about forty thousand of more than a million named species belong to the relatively small lineage of vertebrates.

On the venerable principle that bad situations can always be worse, we can gain some solace by noting the even greater imbalance devised by the founder of modern taxonomy, Carolus Linnaeus. At least we now recognize vertebrates as only part of a single phylum, while most modern schemes divide invertebrates into some twenty to thirty separate phyla. But in his Systema naturae of 1758, the founding document of modern zoological nomenclature, Linnaeus identified only six basic animal groups: four among vertebrates (mammals, birds, reptiles, and fishes) and two for the entire realm of invertebrates (Insecta, for insects and their relatives, and Vermes, literally "worms," for nearly everything else).

When Lamarck became professor of invertebrates at the Museum d'Histoire Naturelle in 1793 (with an official title in a Linnaean straitjacket as professor of insects, and worms), he already recognized that reform demanded the dismemberment of Linnaeus's "wastebucket" category of Vermes. (Wastebucket actually ranks as a semitechnical term among professional taxonomists, a description for inflated groups that become receptacles for heterogeneous bits and pieces that most folks would rather ignore--as in Linnaeus's relegation of all "primitive" animals to the category of "worms," ranking far beneath the notice of specialists on vertebrates.)

In his 1801 book, Systeme des animaux san vertebres, Lamarck identified the hodgepodge of Linnaeus's Vermes as the biggest headache and impediment in zoology:

   The celebrated Linnaeus, and almost all other naturalists up to now, have
   divided the entire series of invertebrate animals into only two classes:
   insects and worms. As a consequence, anything that could not be called an
   insect must belong,  without exception, to the class of  worms.

By the time Lamarck wrote his most famous book, Philosophic zoologique, in 1809, his frustration had only increased; he called Linnaeus's class of worms "une espece de chaos dans lequel les objets tres disparates se trouvent reunis (a kind of chaos where very disparate objects have been united together)." He then blamed the great man himself for this sorry situation: "The authority of this scientist carried such great weight among naturalists that no one dared to change this monstrous class of worms." (By writing cette classe monstrueuse, I am confident that Lamarck meant to attack the sheer numbers of included genera, not the moral status, of Linnaeus's Vermes). Lamarck therefore began his campaign of reform by raiding Vermes and gradually adding the extracted groups as novel phyla to his newly named category of invertebrates. In his first museum lecture course in 1793, he had already expanded the Linnaean duality to a ladder of progress with five rungs--mollusks, insects, worms, echinoderms, and polyps (corals and jellyfish)--by liberating three new phyla from the wastebucket of Vermes.

This reform accelerated in 1795, when Georges Cuvier arrived at the museum and began to study invertebrates as well. The two men collaborated in friendship at first, and they surely operated as one mind on the key issue of dismembering Vermes. Thus, during almost every annual course of lectures, Lamarck continued to add phyla, extracting most new groups from Vermes but some from the overblown Linnaean Insecta as well. In year 7 of the French revolutionary calendar (1799), he established the Crustacea (for marine arthropods, including crabs, shrimps, and lobsters), and in year 8 (1800), the Arachnida (for spiders and scorpions). Lamarck's invertebrate classification of 1801 therefore featured a growing ladder of progress, now bearing seven rungs. In 1809 he presented a purely linear sequence of progress for the last time in his most famous book, Philosophie zoologique. His tall and rigid ladder now contained fourteen rungs, as he had added the four traditional groups of vertebrates atop a list of invertebrate phyla that had just reached double digits (see Lamarck's chart, page 84).

So far, Lamarck had done nothing to inspire any reconsideration of the evolutionary views first presented in his Floreal address of 1800. His taxonomic reforms, in this sense, had been entirely conventional in adding weight and strength to his original views. The Floreal statement had contrasted a linear force leading to progress in major groups with a lateral force causing local adaptation in particular lineages. In 1800 his ladder had included only seven groups. By 1809 he had doubled its length while preserving the same strictly linear form-thus strengthening his central contrast between two forces by granting the linear impetus a greatly expanded field for its inexorably exceptionless operation.

But if Lamarck's first reform of Linnaeus--the expansion of groups into a longer linear series--had conserved and strengthened his original concept of evolution, he now embarked upon a second reform, destined (though he surely had no inkling at the outset) to yield the opposite effect of forcing a fundamental change in his view of life. He had, heretofore, only extracted misaligned groups from Linnaeus's original Vermes. He now needed to consider the core of Vermes itself and to determine whether waste and rot existed at the foundation as well.

"Worms," in our vernacular understanding, are defined both broadly and negatively (bad criteria spelling inevitable trouble down the road) as soft-bodied, bilaterally symmetrical animals, roughly cylindrical in shape and lacking appendages or prominent sense organs. By these criteria, both earthworms and tapeworms fill the bill. For nearly ten years, Lamarck did not seriously challenge this core. But he could not permanently ignore the glaring problem (recognized but usually swept under the rug by naturalists) that this broad vernacular category seemed to include at least two kinds of organisms bearing little relationship beyond a superficial and overt similarity of external form. On the one hand, a prominent group of free-living creatures--earthworms and their allies--built bodies composed of rings or segments and also developed internal organs of substantial complexity, including nerve tubes, blood vessels, and a digestive tract. But another assemblage of largely parasitic creatures--tapeworms and their allies--grew virtually no discretely recognizable internal organs at all and therefore seemed much "lower" than earthworms and their kin by Lamarck's own favored concept of an organic scale of complexity. Would the heart of Vermes therefore need to be dismembered as well?

This problem was already worrying Lamarck when he published the Floreal address in his 1801 compendium on invertebrate anatomy, but he was not yet ready to impose a formal divorce upon the two basic groups of "worms." Either standard of definition, taken by itself--different anatomies or disparate environments--might not offer sufficient impetus for taxonomic separation. But the two criteria correlated perfectly in the remaining Vermes: the earthworm group possessed complex anatomy and lived freely in the outside world; the tapeworm group maintained maximal simplicity among mobile animals and lived almost exclusively within the bodies of other creatures. Lamarck therefore opted for an intermediary solution. He would not yet dismember Vermes but would establish two subdivisions within the class: vets externes (external worms) for earthworms and their allies and vers intestins (internal worms) for tapeworms and their relatives. He stressed the simple anatomy of the parasitic subgroup and defended their new name as a spur to further study, while arguing that knowledge remained insufficient to advocate a deeper separation:

   It is very important to know them [the internal worms], and this name will
   facilitate their study. But aside froth this motive, I also believe that
   such a division is the most natural ... because the internal worms art'
   much more imperfect and simply organized than the other worms.
   Nevertheless, we know so little about their origin that we cannot yet make
   them a separate order.

At this point the crucial incident occurred that sparked Lamarck to an irrevocable and cascading reassessment of his evolutionary views. He attended Cuvier's lecture during the winter of 1801-1802 (year 10 of the revolutionary calendar) and became convinced by his colleague's elegant data on the anatomy of external worms that the differences between his two subdivisions were too great to permit their continued residence in the same class. He would, after all, have to split the heart of Vermes. In his next lecture course, in the spring of 1802, Lamarck formally established the class Annelida for the external worms (retaining Vermes for the internal worms alone) and then separated the two classes widely by placing his new annelids above insects in linear complexity while leaving the internal worms near the bottom of the ladder, well below insects.

Lamarck formally acknowledged Cuvier's spur when he wrote a history of his successive changes in classifying invertebrates for the Philosophie zoologique of 1809:

   Mr. Cuvier discovered the existence of arterial and venous vessels in
   distinct Animals that had been confounded with other very differently
   organized animals under the name of worms. I soon used this new fact to
   perfect my classification; therefore, I established the class of Annelids
   in my course for year 10 [1802].

The handwritten note and drawing in the interleaved copy of Lamarck's 1801 book, published last month in the first installment of this essay, tells much the same story--but what a contrast, in both intellectual and emotional intrigue, between a sober memory written long after an inspiration and the inky evidence of the moment of enlightenment itself!

But this tale should now be raising questions in the minds of readers. Why am I making such a fuss about this particular taxonomic change: the final division of Vermes into a highly ranked group of annelids and a primitive class of internal worms? In what way does this alteration differ from any other change in classification previously discussed? In all cases, Lamarck subdivided Linnaeus's class Vermes and established new phyla in his favored linear series, thus reinforcing his view of evolution as built by contrasting forces of linear progress and lateral adaptation. Wasn't he just following the same procedure in extracting annelids and placing them on a new rung of his ladder? So it might seem--at first. But Lamarck was too smart, and too honorable, to ignore a logical problem directly and inevitably instigated by this particular division of worms--and the proper solution broke his system.

At first, Lamarck did treat the extraction of annelids as just another addition to his constantly improving linear series. But as the years passed, he became more and more bothered by an acute problem evoked by an inherent conflict between this taxonomic decision and the precise logic of his overarching system. Lamarck had ranked the phylum Vermes, now restricted to the internal worms alone, just above a group he named radiaires (radially symmetrical animals)--actually (by modern understanding) a false amalgam of jellyfishes from the coelenterate phylum and sea urchins and their relatives from the echinoderm phylum. Worms had to rank above radiates because bilateral symmetry and directional motion trump radial symmetry and an attached (or not very mobile) lifestyle--at least in conventional views about ladders of progress (which, of course, use mobile and bilaterally symmetrical humans as the ultimate standard). But the parasitic internal worms lack the two most important organ systems--nerve ganglia and cords, and circulatory vessels--that virtually define complexity on the traditional ladder. Yet echinoderms, within the "lower" radiate phylum, develop both nervous and circulatory systems. They circulate seawater rather than blood, but they do run their fluids through tubes.

If Lamarck's primary "force that tends incessantly to complicate organization" truly works in a universal and exceptionless manner, then how can such an inconsistent situation arise? If the force be general, then any given group must stand fully higher or lower than any other. A group cannot be higher for some features but lower for others. Taxonomic experts cannot pick and choose. He who lives by the line must die by the line.

This problem did not arise so long as annelids remained in the class of worms. Lamarck, after all, had never argued that each genus of a higher group must rank above all members of a lower group in every body part. He only claimed that the "principal masses" of organic design run in pure linear order. Individual genera may degenerate or adapt to less complex environments--but so long as some genera display the higher conformation in all features, then the entire group retains its status. In this case, so long as annelids remained, then many worms possessed organ systems more complex than any comparable structure in any lower group--and the entire class of worms could retain its unambiguous position above radiates and other primitive forms. But with the division of worms and the banishment of complex annelids, Lamarck now faced the logical dilemma of a coherent group (the internal parasitic worms) standing higher than radiates in some key features but lower in others. The pure march of nature's progress--the keystone of Lamarck's entire system--had been fractured.

Lamarck struggled with this problem for several years. He stuck to the line of progress in 1802 and again--for the last time, and in a particularly uncompromising manner that must, in retrospect, have been a last hurrah before the fall--in the first volume of his seminal work, the Philosophie zoologique of 1809. But honesty eventually trumped hope. Just before publication, Lamarck appended a short chapter of additions to volume two of the Philosophic zoologique. He now, if only tentatively, floated a new scheme that would resolve his problem with worms but also unravel his precious linear system.

Lamarck had always argued that life began with the spontaneous generation of infusorians (single-celled animals) in ponds. But suppose that spontaneous generation occurs twice and in two distinct environments--in the external world, for a lineage beginning with infusorians, and inside the bodies of other creatures, for a second lineage beginning with worms? Lamarck therefore wrote that "worms seem to form one initial lineage in the scale of animals, just as, evidently, the infusorians form the other branch."

Lamarck then faced the problem of allocating the higher groups. To which of the two great lines does each belong? He presented his preliminary thoughts in a chart--perhaps the first evolutionary branching diagram ever published in the history of biology--that directly contradicted his previous image of a single ladder (compare the later chart, page 86, with the version above, taken from volume one of the same 1809 work). Lamarck begins (at the top, contrary to current convention) with two lines, one labeled infusoires (single-celled animals) and the other vers (worms). He then inserts light dots to suggest possible allocations of the higher phyla to the two lines. The logical problem that broke his system has now been solved--for the radiaires, standing below worms in some features but above in others, now rank in an entirely separate series, directly following an infusorian beginning.

When mental floodgates open, the tide of reform must sweep to other locales. Once he had admitted branching and separation at all, Lamarck could hardly avoid the temptation to apply this new scheme to other old problems. Therefore, he also suggested some substantial branching at the end of his array. He had always been bothered by the conventional summit of reptiles to birds to mammals, for birds seemed just different from, rather than inferior to, mammals. Lamarck therefore proposed (and drew on his revolutionary chart) that reptiles branched at the end of the series, one line passing from turtles to birds (oiseaux) to monotremes (platypuses, which Lamarck now considered as separate from mammals), and the other from crocodiles to marine mammals (labeled m. amphibies) to terrestrial mammals. Finally, and still in the new spirit, he even posited a threefold branching in the transition to terrestrial mammals, leading to separate lines for whales (m. cetaces), hoofed animals (m. ongules), and mammals with nails (m. onguicules), including carnivores, rodents, and primates.

Finally, Lamarck explicitly connected the two reforms: the admission of two sequences of spontaneous generation at the bottom and a branching among higher vertebrates at the top: "The animal scale begins with at least two branches; in the course of its extent, several branches seem to end in different places."

After the Philosophie zoologique of 1809, Lamarck wrote one additional major book on evolution, the introductory volume (1815) of his Histoire naturelle des animaux sans vertebres. Here he transcended all the tentativeness of his 1809 revision and announced his conversion to branching as the fundamental pattern of evolution. In direct contradiction to the linear model that had shaped all his previous work, Lamarck stated simply and without ambiguity: "Dans sa production des differents animaux, la nature n'a pas execute une serie unique et simple. (In its production of the different animals, nature has not fashioned a single and simple series.)"

He then emphasized the branching form of his new model and explained how the division of worms, inspired by Cuvier's observations, had broken his former system and impelled his revision:

   The order is far from being simple; it is branching (rameux) and even
   appears to be constructed of several distinct series.... The animals that
   belonged to the class of worms display a great disparity of
   organization.... The most imperfect of these animals arise by spontaneous
   generation, and the worms [now restricted to vers intestins, with annelids
   removed/ truly form their own series, later in origin than the one that
   began with infusorians.

Lamarck's third and last chart (page 88, reproduced from his 1815 volume) shows how far he had progressed both in his own confidence and in copious branching on his new tree of life. He titles the chart "Presumed order of the formation of animals, showing two separate and subbranching series." Note how the two major lines of separate spontaneous generation--one beginning with infusorians, the other with internal worms--are now clearly marked and separated. Note also how each series also divides within itself, thus establishing the process of branching as a key theme at all scales of the system. The infusorian line branches at the level of polyps (corals and jellyfish) into a line of radiates and a line terminating in mollusks. The second line of worms also branches in two, leading to annelids on one side and insects on the other. But the insect line then splits again (a tertiary division) into a lineage of crustaceans and barnacles (labeled cirrhipedes) and another of arachnids (spiders and scorpions).

Finally, we must recognize that these major changes do not affect only the overt geometry of animal organization. The conversion from linearity to branching also--and perhaps even more importantly--marks a profound shift in Lamarck's underlying theory of nature. He had based his original system, defending it vociferously until 1809, on a fundamental division of two independent forces--a primary cause that builds basic anatomies in an unbroken line of progress and a subsidiary lateral force that draws single lineages off the line into byways of immediate adaptation to local environments. A set of philosophical consequences then spring from this model: the predictable and lawlike character of evolution lies patent in the primary force and its ladder of progress reaching to man, while accidents of history (leading to local adaptations) can then be dismissed as secondary and truly independent from the overarching order.

But the branching system destroys this neat and comforting scheme for two major reasons. First of all, the two forces become intermingled and conflated in the branching itself. We can no longer distinguish two independent and orthogonal powers working at right angles. Progress may occur along any branch, to be sure, but the very act of division implies an environmental impetus to split the main line--and Lamarck had always advocated a complete and principled distinction between a single and inexorable main line and the numerous minor deviations that can draw off a long-necked giraffe or an eyeless mole but can never disrupt or ramify the major designs of animal life. In the new model, however, environment intrudes at the first construction of basic order--as one group arises spontaneously in ponds, and another inside the bodies of other creatures! Moreover, each of the two resulting lines then branches further, and unpredictably, under environmental impetuses that were not supposed to derail the force of progress among major groups, as when insects split into a terrestrial line of arachnids and a marine line leading to crustaceans and barnacles.

Secondly, the forces of history and natural complexity had now triumphed over the scientific ideal of a predictable and lawlike system. The taxonomy of animals could no longer embody an overarching plan of progress, illustrating the fundamental order, harmony, and predictable good sense of the natural world (and perhaps even the explicit care of a loving deity, whose plans we may hope to understand because he thinks as we do). Now the confusing, particular, local, and unpredictable forces of complex environments held sway, ready at any time to impose a deviation upon any group with enough hubris to suppose that Emerson's forthcoming words could describe their inevitable progress:

   And, striving to be man,
   the worm

   Mounts through all the
   spires of form.

VI. Lamarck's Epilogue and My Own

Following his last and greatest treatise on the anatomy of invertebrate organisms, Lamarck published only one other major work: Analytic System of Positive Knowledge of Man (1820). This rare book has not been consulted by previous historians who traced the development of Lamarck's changing views on the classification of animals. Thus, traditional accounts stop at Lamarck's 1815 revision, with its fundamental distinction between two separate lineages of spontaneous generation. The impression therefore persists that Lamarck never fully embraced the branching model, later exemplified by Darwin as the "tree of life," with a common trunk of origin for all creatures and no main line of growth thereafter. Lamarck had compromised his original ladder of progress by advocating two separate origins for living things, but he could continue to stress linearity in each of the resulting series.

But his 1820 book, although primarily a treatise on psychology, does include a chapter on the classification of animals, and I was excited to find that Lamarck does pursue his revisionary path further and does finally arrive at a truly branching model for a tree of life. Moreover, in a remarkable passage, Lamarck also recognizes the philosophical implications of his full switch by acknowledging a reversal in his ranking of natural forces--one of the most interesting (and honorable) intellectual conversions I have ever read.

Lamarck still talks about forces of progress and forces of branching, and he does argue that progress will proceed along each branch. But branching has triumphed as a primary and controlling theme, and Lamarck now frames his entire discussion of animal taxonomy in terms of successive points of division. For example, consider this epitome of vertebrate evolution:

   Reptiles come necessarily after fishes. They build a branching sequence,
   with one branch leading from turtles to platypuses to the diverse group of
   birds, while the other seems to direct itself, via lizards, toward the
   mammals. The birds then ... build a richly varied branching series, with
   one branch ending in birds of prey.

In previous models, he had viewed birds of prey as the top rung of a single avian ladder.

But much more radically, his 1815 model, based on two lines of spontaneous generation, has now disappeared. In its place, Lamarck advocates the same tree of life that would later become conventional through the influence of Darwin and other early evolutionists. Lamarck now proposes a single common ancestor for all animals, called a monad. From this beginning, infusorians evolve, followed by polyps, arising "directly and almost without a gap." But polyps then branch to build the rest of life's tree. "Instead of continuing as a single series, the polyps appear to divide themselves into three branches": the radiates, which end without evolving any further; the worms, which continue to branch into all phyla of segmented animals, including annelids, insects, arachnids, crustaceans, and barnacles, each by a separate event of division; and the tunicates (now regarded as marine organisms closely related to vertebrates), which later split to form several lines of mollusks and vertebrates.

Lamarck then acknowledges the profound philosophical revision implied by a branching model for nature's fundamental order. He had always viewed the linear force of progress as primary. As late as 1815, even after changing his model to permit extensive branching and two environmentally induced sequences of spontaneous generation, Lamarck continues to emphasize the primary power of the linear force compared with disturbing and anomalous exceptions produced by lateral environmental causes, called l'influence des circonstances. I quoted his key passage in the first installment of this essay:

   The plan followed by nature in producing animals clearly comprises a
   predominant prime cause. This endows animal life with the power to make
   organization gradually more complex.... Occasionally a foreign, accidental,
   and therefore variable cause has interfered with the execution of the plan
   ... [producing] branches that depart from the series in several points and
   alter its simplicity.

But five years later, in his final book of 1820, Lamarck now rejects this controlling concept of his career and embraces the opposite conclusion. The influence of circumstances (leading to a branching model of animal taxonomy) rules the paths of evolution. All general laws--of progress or anything else--must be subservient to the immediate singularities of environments and histories. The influence of circumstances has risen from the position of a disturbing and peripheral joker to true lord of all (with an empire to boot):

   Let us consider the most influential cause for everything done by nature,
   the only cause that can lead to an understanding of everything that nature
   produces.... This is, in effect, a cause whose power is absolute, superior
   even to nature, since it regulates all nature's acts, a cause whose empire
   embraces all parts of nature's domain.... This cause resides in the power
   that circumstances have to modify all operations of nature, to force nature
   to change continually the laws that she would have followed without [the
   intervention of] these circumstances, and to determine the character of
   each of her products. The extreme diversity of nature's productions must
   also be attributed to this cause.

Lamarck's great intellectual journey began with a first public address about evolution, delivered in 1800 during a month that the revolutionary government had auspiciously named Floreal, or flowering. He then developed the first comprehensive theory of evolution in modern science--an achievement that won him a secure place in any scientific hall of fame or list of immortals--despite the vicissitudes of his reputation during his own lifetime and immediately thereafter.

But Lamarck's original system failed--and not for the reasons we specify today in false hindsight (the triumph of Mendelism over Lamarck's false belief in inheritance of acquired characters) but from inconsistencies that new information imposed upon the central logic of Lamarck's system during his own lifetime. We can identify a fulcrum, a key moment, in the unraveling of Lamarck's original theory: when he attended a lecture by Cuvier on the anatomy of annelids and recognized that he would have to split his taxonomic class of worms into two distinct groups. This recognition--which Lamarck recorded with excitement (and original art) as a handwritten insertion into his first published book on evolution--unleashed a growing cascade of consequences that, by Lamarck's last book of 1820, destroyed his original theory of primary ladders of progress versus subsidiary lateral deviations and led him to embrace the opposite model (in both geometry of animal classification and basic philosophy of nature) of a branching tree of life.

A conventional interpretation would view this tale as fundamentally sad, if not tragic, and would surely note a remarkable symbol and irony for a literary conclusion. Lamarck began his adventure in the springtime month of flowering. But he heard Cuvier's lecture, and his system began to crumble, on the eleventh day of Nivose, the winter month of snow. How fitting--to begin with springtime joy and promise, and to end in the cold and darkness of winter. How fitting, in one distorted sense--but how very, very wrong. I do not deny or belittle Lamarck's personal distress, but how can we view his slow acknowledgment of logical error, and his willingness to construct an entirely new and contrary explanation, as anything other than a heroic act, worthy of our greatest admiration and identifying Lamarck as one of the finest intellects in the history of biology (a name that he invented for his profession)?

Two major reasons lead me to view Lamarck's intellectual odyssey in this eminently positive light. First, what can be more salutary in science than the flexibility that allows a person to change his mind, and to do so not for a minor point, under the compulsion of irrefutable data, but to rethink and reverse the most fundamental concept underlying a basic philosophy of nature. I would argue, secondly, that Lamarck's journey teaches us something truly important about the interaction between nature and our attempts to understand her ways. The fallacies and foibles of human thinking lead us into systematic and predictable trouble when we try to grasp the complexities of external reality. Among these foibles, our persistent attempts to build abstractly beautiful, logically impeccable, and comprehensively simplified systems always lead us astray. Lamarck far exceeded most of us in his attraction to this perilous style of theorizing--this esprit de systeme--and he therefore fell further and harder because he also possessed the honesty and intellectual power to probe his mistakes.

Nature, to cite a modern cliche, always bats last. She will not succumb to the simplicities of our hopes or mental foibles, but she remains eminently comprehensible. Evolution follows the syncopated drumbeats of complex and contingent histories, shaped by the vagaries and uniquenesses of time, place, and environment. Simple laws with predictable outcomes cannot fully describe the pageant and pathways of life. A linear march of progress must raft as a model for evolution, but a luxuriantly branching tree does capture the basic geometry of history.

When Lamarck snatched victory from the jaws of his defeat (by abandoning his beloved ladder of life and embracing the tree), he stood in proper humility before nature's complexity--a lesson for us all. But he also continued to wrestle with nature, to struggle to understand and even to tame her ways, not simply to bow down and acknowledge sovereignty. Only the most heroic people can follow Job's great example in owning error while continuing to hurl defiance and shout, "I am here." Lamarck greeted nature (traditionally construed as female) with Job's ultimate challenge to God (construed as male, in equally dubious tradition): "Though he slay me, yet will I trust in him; but I will maintain mine own ways before him" (Job 13:15).

I therefore propose that we reinterpret the symbolic meaning of Lamarck's undoing in the month of Nivose. Cuvier's challenge elicited a cascade of discovery and reform, not the battering of bitter defeat. And snow also suggests metaphors of softness, whiteness, and purification--not only of frost, darkness, and destruction. God, in a much kinder mood than he showed to poor Job, promises his people in the first chapter of Isaiah: "Though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool" (Is. 1:18). We should also remember that this verse begins with an even more famous statement--a watchword for an intellectual life, and a testimony to Lamarck's brilliance and flexibility: "Come now, and let us reason together."

Stephen Jay Gould teaches biology, geology, and the history of science at Harvard University. He is also the Frederick P. Rose Honorary Curator in Invertebrates at the American Museum of Natural History.

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