This first set of Lamarckian ideas contains nothing that should have offended Darwin, while several points embody the deeper functionalist and adaptationist spirit of the Darwinian view of life. Darwin did not grant such crucial emphasis to soft inheritance, although he accepted the principles of use and disuse and inheritance of acquired characters, and he awarded them a subsidiary role in his own theory. But two key items in this first set might be designated as decidedly Darwinian in spirit, if only because they advance and presage two of the half dozen most important ideas in Darwin's theory: the uniformity of environmental change,* and the functionalist first principle that change of habit sets the pathway to altered form. The mechanisms of change differ to be sure — altered habits establish new selection pressures for Darwin, but induce heritable modifications more directly for Lamarck — but both thinkers share a functionalist commitment.
I would argue that the structuralist-functionalist dichotomy precedes any particular theory of mechanism within either camp. Thus, we may view Lamarck and Darwin as occupying the common ground of functionalism, with their differing mechanisms of natural selection and soft inheritance as versions of the same deeper commitment. Therefore, if Lamarckism only encompassed this first set of ideas, we might interpret Lamarck as the inception of a smooth transition to Darwin. But Lamarckism also includes a second set of concepts, which, when combined with the first set into Lamarck's full system, builds an evolutionary theory truly opposed to Darwin's chief theoretical concept and operational principle as well.
The second set: progress and taxonomy
The first set, by itself, leads to a logical dilemma for Lamarck's view of life and his professional commitments. Adaptation to changing local environments may be well explained, but Lamarck's truly ahistorical uniformitarianism implies that life can manifest no progress, or no linear order at all, if adaptation matches creatures to an environmental history without direction. [Page 180] (This issue arose for many environmental determinists in both creationist and evolutionist camps. Buckland, and most of his catastrophist colleagues, maintained their allegiance to life's increasing perfection by positing a directional history of environmental change — increasing inclemency, for example, requiring improvement in organic design to meet the growing challenge. This option was not open to Lamarck, who espoused a steady state, non-directionalist geology.)
Yet Lamarck firmly advocated a taxonomic ordering of organisms by the conventional scheme of increasing perfection in organization. This subject greeted him on a daily basis, for he held the post of curator for invertebrates at the Museum in Paris, and his yearly courses featured this organizing theme of linear order. (As a pedagogic device, Lamarck usually started with humans, as the “highest” creature, and then discussed the rest of nature as degradation from maximal complexity. He defended this procedure, even in his evolutionary writings, as a method for teaching, even though historical order had actually moved from simple to complex — for he argued that one must understand the full and final possibilities before grasping the imperfect and incipient beginnings.)
Lamarck argued that a second set of forces, distinct from the causal flow of environment to organism, produced nature's other primary pattern of advancing complexity. But this claim for an efficient and universal cause of progress engendered another dilemma: why, on our present and ancient earth, do some organisms still maintain the simplest anatomies? Why were these forms not pushed up the ladder of complexity ages ago? Lamarck resolved this problem with the last major argument of his full system — continuous spontaneous generation. New life continues to arise from chemical constituents; these simple forms begin their march up the ladder, while replacements at their lowly status continue to form anew. (Thus, in a curious sense, as Simpson and others have noted, Lamarck's evolutionary system operates as a grand steady state, even as any particular bit of protoplasm moves on a historical path up the sequence. The ladder of life really operates as a continuous escalator, with all steps occupied at all moments. The simplest forms continue to arise by spontaneous generation from chemical constituents formed by the breakdown of higher creatures upon their individual deaths.)
Lamarck argued that his unconventional chemistry, emphasizing the role of fire and the motions of subtle fluids, engendered these two central phenomena — spontaneous generation and progress up the ladder — as consequences of deeper physical principles. Lavoisier had destroyed the old quadripartite taxonomy of air, water, earth, and fire in developing his theory of chemical elements. Lamarck opposed the “new chemistry” by asserting the old taxonomy, and his own distinctive claim for the primacy of fire. Much of Cuvier's disdain focused not on Lamarck's biology, but on his allegiance to this antiquated chemistry.
Lamarck, who excelled in crisp assertion but not in clear exposition, never fully specified why chemicals should aggregate to life, or what subtle motions [Page 181] of physical fluids would build the increasing complexity of anatomy. He held that the products of spontaneous generation arose as small, soft and un-differentiated primal forms. The complexifying force — which Lamarck usually called le pouvoir de la vie or la force qui tend sans cesse a composer I'organisation — resides in the motion of fluids and their inevitable tendency to carve channels, sacs, and passageways in soft tissues. This process, extended through time, gradually builds ever greater complexity. In the Histoire naturelle of 1815, Lamarck offers his most explicit statement about this process: “As the movement of fluids . . . accelerates, the vital forces would grow proportionately, and so will their power. The rapid motion of fluids will etch canals between delicate tissues. Soon their flow will begin to vary, leading to the emergence of distinct organs. The fluids themselves, now more elaborate, will become more complex, engendering a greater variety of secretions and substances composing the organs” (1815, in Corsi, 1988, p. 189).
Lamarck did clearly assert that these internal carvings of complexity maintained a relentless and intrinsic causal basis separate from the apparatus of response to “felt needs” used in building adaptations to changing local environments. He contrasted the two sets of forces in writing: “There exists a variety of environmental factors which induces a corresponding variety in the shapes and structure of animals, independent of that special variety which necessarily results from the progress of the complexity of organization in each animal” (1809, p. 112). He also stated that the entire escalator of complexity could run a full course in a constant environment: “If nature had given existence to none but aquatic animals and if all these animals had always lived in the same climate, the same kind of water, the same depth, etc., etc., we should then no doubt have found a regular and even continuous gradation in the organization of these animals” (1809, p. 69).
Lamarck therefore proposes two distinct sets of forces to construct what he regarded as the two preeminent features of life — progress in linear order, and adaptation to environment. The interactions of these sets — not the causes or properties of either one — establish the foundation of Lamarckism, properly defined in his own expansive terms.
Distinctness of the two sets
I shall argue in the next section that these two sets of concepts must be regarded as both logically distinct and opposed in Lamarck's system. My basis for regarding Lamarckism as a theory of hierarchy lies in this division. Lamarck, as we shall see, always presents the two sets as separate in his later evolutionary writing, and scholars of Lamarckism have accepted this contrast as crucial (Burkhardt, 1977; Mayr, 1972; Simpson, 1961). But Lamarck, as noted several times above, remains a frustrating figure for historians. His assertions are bold, even dogmatic; but his arguments tend to be sketchy, full of elisions, or even self-contradictory. These frustrations become most apparent in Lamarck's treatment of his two primary forces (as Corsi, 1988, has discussed with great insight). The explicit assertions of his later works rank the two forces as distinct and opposed, but both the ontogeny and logic of [Page 182] Lamarck's arg
ument shows more “leakage” than his words would suggest. Consider the following, as stressed by Corsi and Burkhardt:
Ontogeny. Although Lamarck presents the forces of adaptation as deviations from, and therefore secondary to, the primary causes that build complexity, he apparently developed his mechanism for progress from his previously formulated ideas about adaptation (Corsi, 1988; and newly discovered evidence in Gould, 2000d). Still, the psychological source of a theory needn't map its eventual logical structure, and this point, while interesting, scarcely compromises the distinctness and ranking of the two sets.
Causation. At several points, Lamarck breaches the boundaries between his sets in discussing causation.
(1) Soft inheritance works in both sets. Whether an organism becomes more complex because fluids carve channels by intrinsic chemistry, or becomes better adapted because habits change in response to altered environments, the acquired features must still be passed to offspring by direct inheritance. Still, a common mechanism may work in two modes, and this linkage does not compromise Lamarck's claim for distinctness.
(2) The style of action for soft inheritance in adaptation depends upon the state of complexity engendered by opposing forces of progress. Lamarck divided organisms into three ascending groups designated, in the old Aristotelian terms, as insensitive, sensitive, and rational. The first group, too simple to mount a creative response to external change, reacts to environment not by altered habits, but by direct influence. The capacity for active response, Lamarck's famous sentiment interieur, only arises in the second group and unleashes the tripartite causal sequence of changed environment to altered habit to modified form.
(3) The real blurring occurs when we try to make sense of Lamarck's claim that forces of progress can build the entire sequence from infusorian to complex vertebrate without any environmental change. Lamarck surely makes this assertion explicitly, without hesitation (see citation on p. 187), and the distinctness of his two forces depends upon this potential independence. But Lamarck does not work out a consistent justification, and several frustrated historians have even argued that he could not have done so without contradiction — that his system, in other words, suffers from a true defect in logic of argument on this point.
The simplest organisms, Lamarck states, are carved out and complexified by “subtle” and “imponderable” fluids — caloric and electricity in his system. These fluids work in their intrinsic way to produce increased complexity. But as animals differentiate and harden, fluids must flow in preset channels; the weak imponderables then lose their power to mold, and the body's own ponderable fluids must assume this role. (Lamarck locates this transition at about the echinoderm grade of organization.) At this level, the “power of life” should become inoperable without an impetus from environmental change — and the two sets of forces should therefore commingle. Protected inside a rigid body, and constrained to flow in preexisting channels, how can the ponderable [Page 183] fluids produce further advances in complexity unless changed environments elicit altered habits, thus modifying form and permitting the ponderables to flow in new ways (see Corsi, 1988, p. 200; and Burkhardt, 1977, p. 147).
Pattern. The “pure” distinction of progress and adaptation should produce a single linear chain (for progress) with lateral deflections (for adaptation). Lamarck tried to construct such a topology, but could not carry his scheme to completion at two important places — the top and bottom of the ladder — where environment intruded upon the chain to blur the distinction of forces.
(1) Two sequences of spontaneous generation. Lamarck first proposed a single linear series of animals, starting with the spontaneous generation of infusorians (protistans) as free-living creatures in water. These unicells then aggregated to polyps and their relatives, and then to simple, bilaterally symmetrical worms (see Fig. 3-1). However, Lamarck later discovered worms (the acoelous platyhelminths in modern terminology) without nerve cords. These worms ranked “higher” than polyps on grounds of their mobility, but could not be the descendants of polyps, unless the nerve cords of polyps had degenerated and disappeared — impossibility under the “force that tends incessantly to complicate organization.” Thus, worms without nerve cords must represent part of a second and separate sequence of progress. Lamarck proposed an origin for this second sequence in the spontaneous generation of even simpler worms as parasites within the bodies of other organisms. If
3-1. Lamarck's linear series of animal organization, from volume 1 of the Philosophie zoologique of 1809. (Author's collection.)
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different environments — a pond and the body of a complex creature — encourage disparate inceptions for sequences of progress, then the two forces commingle (Fig. 3-2).
(2) Ramification at the top. Lamarck could not rank the vertebrates in linear order. He followed the conventional path of fish to reptile, but could not convince himself that birds fell between reptiles and mammals in a genealogical sense. He therefore permitted a fork, provoked by the environmental set of forces, at the very top of a ladder supposedly built by the unilinear impetus of progress (Fig. 3-3): “We cannot doubt,” he wrote with characteristic certainty (1809, p. 176), “that the reptiles by means of two distinct branches,
3-2. Lamarck's later conception of two chains of being with different starting points, the first (to the left) from free-living single-celled infusorians, the second (to the right) beginning with parasitic worms spontaneously generated within the bodies of higher organisms. From Lamarck, 1815. (Author's collection.)
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3-3. Lamarck allowed his linear sequence to branch at the apex of complexity (shown as the bottom in this figure because he begins with the lowest forms and works down by descent). Lamarck could not rank birds and mammals as part of the single sequence, and therefore allowed a branch after reptiles with birds on one side (left, culminating in egg-laying monotremes), and mammals to the right. From additional material added to the end of Volume 2 of the Philosophie zoologique of 1809. (Author's collection.)
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caused by the environment, have given rise, on the one hand, to the formation of birds, and, on the other hand, to the . . . mammals.”
I doubt that we can take this analysis much further. Historians often err in trying to wrest consistency from great thinkers at all costs. Some issues are too difficult, too encompassing, too important, too socially embedded, or just too devoid of evidence, for resolution even by the finest scientists. Darwin never consolidated his contradictory ideas about progess (see Chapter 6), and Lamarck never found a thoroughly consistent way to fulfill his desired argument for a full separation between two forces pulling evolution in orthogonal [Page 186] directions — up the ladder of progress, and sideways into lateral paths of adaptation. Lamarck may never have completed his scheme with success and consistency, but he made his desires clear to the point of redundancy. Lamarck's two-factor theory holds the distinction of being both the first evolutionary system in modern Western thought, and a strong argument for causal hierarchy. The two levels — in strong contrast with modern theories of hierarchy — are both causally distinct and contradictory for Lamarck, thus inspiring Darwin's legitimate disparagement. Lamarck's distinction of levels, as discussed in the next section, unites hierarchy and evolution at the starting gate of the subject's modern history.
LAMARCK'S TWO-FACTOR THEORY: THE HIERARCHY OF PROGRESS AND DEVIATION
Lamarck had separated his sets of forces in order to account for the two primary attributes of natural order — features that seemed to play off against, or even to contradict, each other. First, organisms form a progressive sequence from mo»ad to man, but the sequence abounds with gaps and deviations — so some other force must be disrupting a potentially smooth gradation. Second, organisms are well adapted to their environments, but most adaptations, from the tiny eyes of moles to the legendary necks of giraffes, represent particular specializations and depart
ures from type (with many adaptations counting as losses or degenerations); therefore, adaptation cannot account for the sequence of progress.
Lamarck joined the two sets in a discordant union that operated more like a tug of war than a harmony. This partnership made no pretense to equality. A primary and dominating force — the march of progress — struggled to order organisms in a simple and sensible way; while a secondary and disrupting force — l'influence des circonstances, or adaptation to local environments — tore this order apart by pushing individual lineages into lateral deviations from the main track, thereby making the order of life rich, messy, and replete with clumps and gaps. This clear distinction of merit — the regular vs. the deviant, the progressive vs. the merely fit — imparts the character of hierarchy to Lamarck's uneasy marriage of forces, with a primary factor doing its inexorable, underlying work at a higher level, while a secondary but more immediate factor of disruption plays upon the products of this higher level, pushing some forms into the side-channels of its influence. Burkhardt (1977, p. 87) captures both the hierarchy and conflict of forces in his epitome of Lamarck's system as an attempt to explain “how organisms would develop naturally” along a chain of progress “were it not for the constraining accidents of history” pushing lineages into side channels of adaptation.
The Structure of Evolutionary Theory Page 31
