In sketching the life of one of our most celebrated naturalists, we have conceived it to be our duty, while bestowing the commendation they deserve on the great and useful works which science owes to him, likewise to give prominence to such of his productions in which too great indulgence of a lively imagination had led to results of a more questionable kind, and to indicate, as far as we can, the cause or, if it may be so expressed, the genealogy of his deviations.
Cuvier then proceeded to downplay Lamarck’s considerable contributions to anatomy and taxonomy, and to excoriate his senior colleague for fatuous speculation about the comprehensive nature of reality. He especially ridiculed Lamarck’s evolutionary ideas by contrasting a caricature of his own construction with the sober approach of proper empiricism:
These [evolutionary] principles once admitted, it will easily be perceived that nothing is wanting but time and circumstances to enable a monad or a polypus gradually and indifferently to transform themselves into a frog, a stork, or an elephant…. A system established on such foundations may amuse the imagination of a poet; a metaphysician may derive from it an entirely new series of systems; but it cannot for a moment bear the examination of anyone who has dissected a hand … or even a feather.
Cuvier’s éloge reeks with exaggeration and unjust ridicule, especially toward a colleague ineluctably denied the right of response—the reason, after all, for our venerable motto, de mortuis nil nisi bonum (“say only good of the dead”). But Cuvier did base his disdain on a legitimate substrate, for Lamarck’s writing certainly displays a tendency to grandiosity in comprehensive pronouncement, combined with frequent refusal to honor, or even to consider, alternative views with strong empirical support.
L’esprit de système, the propensity for constructing complete and overarching explanations based on general and exceptionless principles, may apply to some corners of reality, but this approach works especially poorly in the maximally complex world of natural history. Lamarck did feel drawn toward this style of system building, and he showed no eagerness to acknowledge exceptions or to change his guiding precepts. But the rigid and dogmatic Lamarck of Cuvier’s caricature can only be regarded as a great injustice, for the man himself did maintain appropriate flexibility before nature’s richness, and did eventually alter the central premises of his theory when his own data on the anatomy of invertebrate animals could no longer sustain his original view.
This fundamental change—from a linear to a branching system of classification for the basic groups, or phyla, of animals—has been well documented in standard sources of modern scholarship about Lamarck (principally in Richard W. Burkhardt,Jr.’s The Spirit of System: Lamarck and Evolutionary Biology, Harvard University Press, 1977; and Pietro Corsi’s The Age of Lamarck, University of California Press, 1988). But the story of Lamarck’s journey remains incomplete, for both the initiating incident and the final statement have been missing from the record—the beginning, because Lamarck noted his first insight as a handwritten insertion, heretofore unpublished, in his own copy of his first printed statement about evolution (the al address of 1800, recycled as the preface to his 1801 book on invertebrate anatomy); and the ending, because his final book of 1820, Système analytique des connaissances positives de l’homme (Analytical system of positive knowledge about man), has been viewed only as an obscure swan song about psychology, a rare book even more rarely consulted (despite a fascinating section containing a crucial and novel wrinkle upon Lamarck’s continually changing views about the classification of animals). Stories deprived of both beginnings and endings cannot satisfy our urges for fullness or completion—and I am grateful for this opportunity to supply these terminal anchors.
II. LAMARCK’S THEORY AND OUR MISREADINGS
Lamarck’s original evolutionary system—the logical, pure, and exceptionless scheme that nature’s intransigent complexity later forced him to abandon—featured a division of causes into two independent sets responsible for progress and diversity respectively. (Scholars generally refer to this model as the “two-factor theory.”) On the one hand, a “force that tends incessantly to complicate organization” (la force qui tend sans cesse à composer l’organisation) leads evolution linearly upward, beginning with spontaneous generation of “infusorians” (single-celled animals) from chemical precursors, and moving on toward human intelligence.
But Lamarck recognized that the riotous diversity of living organisms could not be ordered into a neat and simple sequence of linear advance—for what could come direcdy before or after such marvels of adaptation as long-necked giraffes, moles without sight, flatfishes with both eyes on one side of the body, snakes with forked tongues, or birds with webbed feet? Lamarck therefore advocated linearity only for the “principal masses,” or major anatomical designs of life’s basic phyla. Thus, he envisioned a linear sequence mounting, in perfect progressive regularity, from infusorian to jellyfish to worm to insect to mollusk to vertebrate. He then depicted the special adaptations of particular lineages as lateral deviations from this main sequence.
These special adaptations originate by the second set of causes, labeled by Lamarck as “the influence of circumstances” (l;’influence des circonstances). Ironically, this second (and subsidiary) set has descended through later history as the exclusive “Lamarckism” of modern textbooks and anti-Darwinian iconoclasts (while the more important first set of linearizing forces has been forgotten). For this second set—based on change of habits as a spur to adaptation in new environmental circumstances—invokes the familiar (and false) doctrines now called “Lamarckism”: the “inheritance of acquired characters” and the principle of “use and disuse.”
Lamarck invented nothing original in citing these principles of inheritance, for both doctrines represented the “folk wisdom” of his time (despite their later disproof in the new world of Darwin and Mendel). Thus, the giraffe stretches its neck throughout life to reach higher leaves on acacia trees, and the shorebird extends its legs to remain above the rising waters. This sustained effort leads to longer necks or legs—and these rewards of hard work then descend to offspring in the form of altered heredity (the inheritance of acquired characters, either enhanced by use, as in these cases, or lost by disuse, as in eyeless moles or blind fishes living in perpetually dark caves).
As another irony and injustice (admittedly abetted, in part, by his own unclear statements), the ridicule that has surrounded Lamarck’s theory since Cuvier’s éloge and Darwin’s dismissal has always centered upon the charge that Lamarck’s views represent a sad throwback to the mystical vitalism of bad old times before modern science enshrined testable mechanical causes as the proper sources of explanation. What genuine understanding, the critics charge, can possibly arise from claims about vague and unknowable powers inherent in Ufe itself, and propelling organisms either upward by an intrinsic complexifying force (recalling Molière’s famous mock of vitalistic medicine, exemplified in the statement that morphine induces sleep “quia est in eo virtus dormativa,” because it contains a dormitive virtue) or sideward by some ineffable “willing” to build an adaptive branch by sheer organic effort or desire?
In a famous letter to J. D. Hooker, his closest confidant, Darwin first admitted his evolutionary beliefs in 1844 by contrasting his mechanistic account with a caricature of Lamarck’s theory: “I am almost convinced … that species are not (it is like confessing a murder) immutable. Heaven forfend me from Lamarck nonsense of a ‘tendency to progression,’ ‘adaptations from the slow willing of animals,’ etc.! But the conclusions I am led to are not widely different from his; though the means of change are wholly so.” And Cuvier, in a public forum, ridiculed the second set of adaptive forces in the same disdainful tone: “Wants and desires, produced by circumstances, will lead to other efforts, which will produce other organs…. It is the desire and the attempt to swim that produces membranes in the feet of aquatic birds. Wading in the water … has lengthened the legs of such as frequent the sides of rivers.”
> Lamarck hurt his own cause by careless statements easily misinterpreted in this mode. His talk about an “interior sentiment” (sentiment intérieur) to propel the upward force, or about organisms obeying “felt needs” (besoins in his terminology) to induce sideward branches of adaptation, led to suspicions about mysterious and unprovable vitalistic forces. But in fact, Lamarck remained a dedicated and vociferous materialist all his life—a credo that surely represents the most invariable and insistent claim in all his writings. He constandy sought to devise mechanical explanations, based on the physics and chemistry of matter in motion, to propel both sets of linear and lateral forces. I do not claim that his efforts were crowned with conspicuous success—particularly in his speculative attempts to explain the linear sequence of animal phyla by positing an ever more vigorous and ramifying flow of fluids, carving out spaces for organs and channels for blood in progressively more complex bodies. But one cannot deny his consistent conviction. “La vie … n’est autre chose qu’un phénomène physique” (life is nothing else than a physical phenomenon), he wrote in his last book of 1820. In a famous article, written to rehabilitate Lamarck at the Darwinian centennial celebrations (for The Origin of Species) in 1959, the eminent historian of science C. C. Gillispie wrote: “Life is a purely physical phenomenon in Lamarck, and it is only because science has (quite righdy) left behind his conception of the physical that he has been systematically misunderstood and assimilated to a theistic or vitalistic tradition which in fact he held in abhorrence.”
Lamarck depicted his two sets of evolutionary forces as clearly distinct and destined to serve contrasting ends. The beauty of his theory—the embodiment of his esprit de système—hes in this clean contrast of both geometry and mechanism. The first set works upward to build progress in a stricdy linear series of major anatomical designs (phyla) by recruiting a mechanism inherent in the nature of living matter. The second set works sideward to extract branches made of individual lineages (species and genera) that respond to the influence of external circumstances by precise adaptations to particular environments. (These side branches may be visualized as projecting at right angles, perpendicular to the main trunk of progress. Vectors at right angles are termed orthogonal, and are mathematically independent, or uncorrelated.)
Lamarck made this contrast explicit by stating that animals would form only a single line of progress if the pull of environmental adaptation did not interrupt, stymie, and divert the upward flow in particular circumstances:
If the factor that is incessandy working toward complicating organization were the only one that had any influence on the shape and organs of animals, the growing complexity of organization would everywhere be very regular. But it is not; nature is forced to submit her works to the influence of their environment…. This is the special factor that occasionally produces… the often curious deviations that may be observed in the progression. (1809, Philosophic zoologique; my translations from Lamarck’s original French text in all cases)
Thus, the complex order of life arises from the interplay of two forces in conflict, with progress driving lineages up the ladder, and adaptation forcing them aside into channels set by peculiarities of local environments:
The state in which we find any animal is, on the one hand, the result of the increasing complexity of organization tending to form a regular gradation; and, on the other hand, of the influence of a multitude of very various conditions ever tending to destroy the regularity in the gradation of the increasing complexity of organization. (1809, Philosophic zoologique)
Finally, in all his major evolutionary works, culminating in his multivolumed treatise on invertebrate anatomy (1815), Lamarck honored the first set of linear forces as primary, and identified the second set as superposed and contrary—as in this famous statement, marking the lateral pull of adaptation as foreign, accidental, interfering, and anomalous:
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, without, however, destroying it. This has created gaps in the series, in the form either of terminal branches that depart from the series in several points and alter its simplicity, or of anomalies observable in specific apparatuses of various organisms. (1815, Histoire naturelle des animaux sans vertèbres)
III. THE VALUES OF CHANGING THEORIES
Charles Darwin began the closing paragraph of his Origin of Species by noting the appeal of evolutionary explanation: “There is grandeur in this view of life.” No thinking or feeling person can deny either nature’s grandeur or the depth and dignity of our discovery that a history of evolution binds all living creatures together. But in our world of diverse passions and psychologies, primary definitions (and visceral feelings) about grandeur differ widely among students of natural history. Darwin emphasized the bounteous diversity itself, in all its buzzing and blooming variety—for the last sentence of this closing paragraph contrasts the “dullness” of repetitive planetary cycling with the endless expansion and novelty of evolution’s good work: “whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
But I suspect that Lamarck, following his own upbringing in the rigorous traditions of French rationalism during the Enlightenment, construed the primary definition of grandeur quite differendy. As a devotee of l’esprit de système, Lamarck surely viewed the capacity of the human mind (his own in this case, for he was not a modest man) to apprehend the true and complete system of nature’s rational order as a primary criterion (with the actual production of riotous diversity as a consequence requiring taxonomie arrangement, but only a product of the less important lateral set of adaptive forces that disturb the march of progress). Thus, the logical clarity of his two-factor theory—with a primary cause establishing a linear march of rational progress and an opposed and subsidiary cause generating a more chaotic forest of adaptive diversity—must have struck Lamarck as the defining ingredient of nature’s grandeur and the power of evolution.
Our understanding of nature must always reflect a subtle interaction between messages from genuine phenomena truly “out there” in the real world and the necessary filtering of such data through all the foibles and ordering devices internal to the human mind and its evolved modes of action (see chapter 2). We cannot comprehend nature’s complexity—particularly for such comprehensive subjects as evolution and the taxonomie structure of organic diversity—unless we impose our mental theories of order upon the overt chaos that greets our senses. The different styles followed by scientists to balance and reconcile these two interacting (but partly contradictory) sources of order virtually define the rich diversity of fruitful approaches pursued by a profession too often, and falsely, caricatured as a monolithic enterprise committed to a set of fixed procedures called “the scientific method.”
Dangers and opportunities attend an overemphasis on either side. Rigid sys-tematizers often misconstrue natural patterns by forcing their observations into rigidly preconceived structures of explanation. But colleagues who try to approach nature on her own terms, without preferred hypotheses to test, risk either being overwhelmed by a deluge of confusing information or falling prey to biases that become all the more controlling by their unconscious (and therefore unrecognized) status.
In this spectrum of useful approaches, Lamarck surely falls into the domain of scientists who place the logical beauty of a fully coherent theory above the messiness of nature’s inevitable nuances and exceptions. In this context, I am all the more intrigued by Lamarck’s later intellectual journey, so clearly contrary to his own inclinations, and inspired (in large part) by his inability to encompass new discoveries about the anatomy of invertebrates into the rigid confines of his beautiful system.
Nothing i
n the history of science can be more interesting or instructive than the intellectual drama of such a slow transformation in a fundamental view of life—from an initial recognition of trouble, to attempts at accommodation within a preferred system, to varying degrees of openness toward substantial change, and sometimes, among the most flexible and courageous, even to full conversion. I particularly like to contemplate the contributions of external and internal factors to such a change: new data mounting a challenge from the outside, coordinated with an internal willingness to follow the logic of an old system to its points of failure, and then to construct a revised theory imposing a different kind of consistency upon an altered world (with minimal changes for those who remain in love with their previous certainties and tend to follow conservative intellectual strategies, or with potentially revolutionary impact for people with temperaments that permit, or even favor, iconoclasm and adventure). Reward and risk go hand in hand, for the great majority of thoroughly radical revisions must fail, even though the sweetest fruits await the few victors in this chanciest and most difficult of all mental adventures.
When we can enjoy the privilege of watching a truly great intellect struggling with the most important of all biological concepts at a particularly interesting time in the history of science, then all factors coincide to produce a wonderful story offering unusual insight into the workings of science as well. When we can also experience the good fortune of locating a previously missing piece—in this case, the first record of a revision that would eventually alter the core of a central theory, although Lamarck, at this inception, surely had no inkling of how vigorously such a small seed could grow—then we gain the further blessing of an intriguing particular (the substrate of all good gossip) grafted onto a defining generality. The prospect of being an unknown witness—the “fly on the wall” of our usual metaphor—has always excited our fancy. And the opportunity to intrude upon a previously undocumented beginning—to be “present at the creation” in another common description—evokes an extra measure of intrigue. In this case, we begin with something almost inexpressibly humble: the classification of worms—and end with both a new geometry for animal life and a revised view of evolution itself.
The Lying Stones of Marrakech Page 15