Lamarck worked his way slowly towards this final system of hierarchy and relative importance. The Floreal lecture of 1800 states that the “principal masses” of major taxonomic units “are almost regularly spaced” (1800, 1984 edition, p. 416), but designates some peculiarly adapted species as “lateral ramifications” and “truly isolated points.” But this lecture cites only environment [Page 187] as a trigger of change. The Recherches of 1802 adds the theme of “organic movements” forming new organs and faculties in an intrinsic sequence of advance. By the time of his most famous work, the Philosophie zoologique of 1809, Lamarck “was explicit in portraying the diversity of animal form as a result of two separate processes” (Burkhardt, 1977, p. 145), and he had formulated the arguments of hierarchy and relative importance as well. The Histoire naturelle of 1815-1822 then consolidates and advocates the hierarchical two-factor theory even more strongly.
In the Philosophie zoologique, Lamarck begins by claiming that, in an ideally simple world, a single sequence of progress would regulate all taxonomic order:
It may then be truly said that in each kingdom of living bodies the groups are arranged in a single graduated series, in conformity with the increasing complexity of organization and the affinities of the object. This series in the animal and vegetable kingdoms should contain the simplest and least organized of living beings at its anterior extremity, and ends with those whose organization and faculties are most perfect. Such appears to be the true order of nature, and such indeed is the order clearly disclosed to us by the most careful observation and an extended study of all her modes of procedure (1809, p. 59).
But this principle of progress remains insufficient in our actual world, where environmental change elicits adaptations off the main sequence: “It does not show us why the increasing complexity of the organization of animals from the most imperfect to the most perfect exhibits only an irregular gradation, in the course of which there occur numerous anomalies or deviations with a variety in which no order is apparent” (1809, p. 107).
These “anomalies and deviations” are produced by a second, and clearly subsidiary, force — a “special factor” that thwarts the “incessantly working” source of general progress, and riddles the chain with gaps and lateral branches: “If the factor which is incessantly working toward complicating organization were the only one which 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, and this environment everywhere produces variations in them. This is the special factor which occasionally produces . . . the often curious deviations that may be observed in the progression” (1809, p. 69).
This special factor may be identified as environmental adaptation, initiated by changed habits and abetted by soft inheritance in the principles of use and disuse and the hereditary passage of acquired characters: “The environment exercises a great influence over the activities of animals, and as a result of this influence the increased and sustained use or disuse of any organ are causes of modification of the organization and shape of animals and give rise to the anomalies observed in the progress of the complexity of animal organization” (1809, p. 105). [Page 188]
As a primary sign of our estrangement from Lamarck's world, and our lack of understanding for his system, all “standard” textbook examples of Lamarckian evolution ignore his fundamental, higher-level principle of progress, and only cite instances of lateral twigs built as highly specialized adaptations. We do this, I suppose, because adaptation and specialization constitute the major theme in our modern evolutionary vocabulary (in the altered guise of Darwinian causation), while the bulk of Lamarck's system has passed beyond our notice into cognitive dissonance. In any case, every classical example — from eyeless moles, to webbed feet of water birds, to long legs of shore birds, to the blacksmith's strong right arm — ranks as a lateral deviation, not a stage on the main sequence. As for the greatest cliché and exemplar of all, the ubiquitous giraffe of our text-books, happily munching leaves at the tops of acacia trees, Lamarck provides only one paragraph of speculation — with no elaboration, no measurements, no data at all. An example can become a knee-jerk standard for many reasons, with cogent, complete documentation not always prominent among them (see Gould, 1991b, on the evolution of horses and the size of Hyracotherium). Nor does simple repetition enhance the probability of truth! Lamarck wrote this and only this about giraffes (even repeating a common error about differential lengths of fore and hind limbs):
It is interesting to observe the result of habit in the peculiar shape and size of the giraffe (Camelo-pardalis)': this animal, the tallest of the mammals, is known to live in the interior of Africa in places where the soil is nearly always arid and barren, so that it is obliged to browse on the leaves of trees and to make constant efforts to reach them. From this habit long maintained in all its race, it has resulted that the animal's forelegs have become longer than its hind-legs, and that its neck is lengthened to such a degree that the giraffe, without standing up on its hind-legs, attains a height of six meters (1809, p. 122).
The final, complex order of life arises from an interplay of the 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, p. 107). In his strongest characterization of the two forces as conflicting, Lamarck tells us in another passage that “nature's work [of progress] has often been modified, thwarted and even reversed by the influence exercised by very different and indeed conflicting conditions of life upon animals exposed to them throughout a long succession of generations” (1809, p. 81).
Two additional statements in the Philosophie zoologique give dramatic expression to the absolute distinction of the forces, and to their hierarchical character, with progress as primary and regular, and diversity as secondary and disturbing. The first provides a vivid iconography of the two-factor theory: [Page 189] progress builds the regular and rising trunk; diversity snatches some items off this upward highway and pulls them into orthogonal blind alleys — “lateral ramifications” that peter out into “isolated points”: “These irregularities ... are found in those organs which are the most exposed to the influence of the environment; this influence involves similar irregularities in the shape and condition of the external parts, and gives rise to so great and singular a diversity of species that, instead of being arranged like the main groups in a single linear series as a regularly graduated scale, these species often constitute lateral ramifications around the groups to which they belong, and their extremities are in reality isolated points” (1809, p. 59). The second features Lamarck's explicit statement about hierarchy, translated into differential taxonomic levels of attention. The broad forces of progress set relations among orders and classes; smaller and more immediate episodes of adaptation establish species and genera:
Nature . . . has really formed a true scale ... as regards the increasing complexity of organization; but the gradations in this scale . . . are only perceptible in the main groups of the general series, and not in the species or even in the genera. This fact arises from the extreme diversity of conditions in which the various races of animals and plants exist; for these conditions have no relation to the increasing complexity of organization; but they produce anomalies or deviations in the external shape and characters which could not have been brought about solely by the growing complexity of organization (1809, p. 58).
Lamarck's increasing conviction about the distinctness, hierarchical character, and conflicting nature of the two for
ces culminates in his last major work, the Histoire naturelle of 1815-1822. The force of progress has now become a “predominant prime cause,” while adaptation ranks below as occasional and foreign, a disturbance strong enough to disrupt but not to efface nature's deeper law:
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, in Corsi, 1988, p. 189).
ANTINOMIES OF THE TWO-FACTOR THEORY
We have seen how Lamarck formulated and intensified the two-factor theory from his first exposition of evolution in 1800 to his last and most comprehensive works. One might even say, following a developmental metaphor, that the two sets of forces differentiated from an originally more inchoate conglomeration of evolutionary ideas, gradually becoming more different and [Page 190] more sharply defined. As the two sets grew along their orthogonal pathways, they became alternate centers of nucleation for the full realm of evolutionary ideas. All major items of this new conceptual world fell to one side or the other — as though two suns had entered an originally homogeneous universe, and all particles had to enter either one or the other gravitational system. Lamarck's two-factor theory separated the universe of evolutionary concepts into a set of dichotomies best characterized as antinomies, an unfamiliar word designating contradictions between two equally binding principles (and originally used to specify differences between ecclesiastical and secular law when both vied for domination in medieval states). The precipitation of ideas about Lamarck's two axes established a long list of antinomies that, in an important way, has set the agenda of evolutionary biology ever since. Darwin opposed this structure of antinomies; others have advanced strong defenses, in whole or in part. The modern theory of hierarchy depends upon a selective defense, but in a manner radically different from Lamarck's formulation. Consider a few key items:
Ideal order (real) vs. disruption (disturbing). The interpretation of diversification by adaptation as lateral to, and disruptive of, an underlying lawful regularity marks an old tradition that Darwin fought fiercely by elevating the supposed “disturbing” force to the cause, by extrapolation, of all evolution. Curiously, since old traditions die hard, this antinomy remains potent (even under a Darwinian rubric) in the common claim that anagenesis, or evolutionary trends in lineages, should be viewed as distinct from cladogenesis, or diversification — and that speciation is, in Julian Huxley's words (1942, p. 389), “a biological luxury, without bearing upon the major and continuing trends of the evolutionary process.”
Behind this issue, of course, and particularly well expressed in this first antinomy, stands the ancient credo of essentialism. Just as the essence or type never becomes fully incarnate in an actual object (because any material being must be subject to all the slings and arrows of outrageous fortune in our palpable world of accidents), so does the outside world of changing environments deny full expression to the ideal march of progress.
Progress vs. diversity. Lamarck's expression of the fundamental vs. the disruptive; note Huxley's words above for a modern expression.
Internal vs. external, or intrinsic vs. interactive. The march of progress is intrinsically and internally generated as a consequence of the chemical properties of matter; this march represents the “essential” process of life, moving ever forward in the absence of any push or disturbance from external forces. Lamarck makes this contrast explicit in arguing that the march of progress would proceed to smooth completion even in an absolutely constant environment.
Immanence vs. unpredictability. The forces of progress, arising as consequences of chemical laws, generate a set of predictable products inherent in the constitution of nature. Since the chain is constantly replenished by spontaneous generation, all stages exist at all times, and the entire sequence constitutes a permanent part of nature. But the disturbing force of environmental [Page 191] change introduces the oddness and unpredictability of contingency. We can never know exactly what climatic change will occur, which lineage will be diverted into its channel, and how the resulting adaptation will form. Thus, our actual world becomes filled up with unique particulars. Giraffe necks do not arise by first principles of natural law, but as a contingency of dry climates and acacia trees at a particular time and place.
Timeless vs. historical. History requires distinctive moments that tell a story as a sequence of events. The force of progress may confer history upon any particular bolus of protoplasm as it mounts the ladder. But, in a larger sense, this force also cancels the usual meaning of history. Each step becomes predictable and repeatable; and each exists at every time (since spontaneous generation continually replenishes the base). Thus, Lamarck's perfecting force becomes essentially ahistorical. The rungs of the ladder are permanent and always occupied; items pass up and through, but the forms are timeless. Genuine history enters via the disturbing force of environmental adaptation instead. A mole without eyes, a stork with long legs, a duck with webbed feet — all originate as nonrepeatable objects of a historical moment, triggered by a particular change of environment in a unique time and place.
Higher taxa vs. species and genera. Lamarck's two-factor theory is hierarchical. The force of progress — paramount, primary, and underlying — produces patterns of nature at the broadest scale, and therefore forges the relationships among higher taxa in our classifications. The force of adaptation is secondary, disruptive, and subsidiary. It seizes individual lineages and pulls them from the main Sequence into side channels that always peter out as dead ends. This lower-level force produces the smaller units, the species and genera of our taxonomies.
Elusive vs. palpable. This last antinomy does not form part of Lamarck's scheme, but becomes important in later interpretations, particularly in Darwin's refutation. The force of progress lies deeper within and operates at a higher level; the force of adaptation works palpably at the surface of things. One can, at least in principle, observe climates getting colder and elephants growing thick coats of fur in direct response; but advance up the ladder lies further from our view in an abstract distance. Lamarck might have denied that the causes of progress posed any greater difficulty in recognition and observation; in his conceptual world, these forces arose from the chemical nature of matter — and therefore became just as accessible as the immediate causes of adaptation. But when Lamarck's theories of physical causation collapsed, the force of progress became elusive — something operating so slowly, and at such high taxonomic levels, as to be effectively invisible in the here and now of testable science. Darwin based his theory upon a reformulation of this seventh antinomy — by arguing that palpable and immediate forces of adaptation did not oppose an inscrutable and untestable force of progress — but rather became the source of progress as well (and hence the only primary cause of all evolution) when extrapolated, by principles of uniformitarianism, into the immensity of time. All evolution therefore entered the realm of the testable. [Page 192]
Modern evolutionists may read this list with an odd feeling of deja vu — in the backward sense that we have already encountered all these issues in the modern debates of our own professional careers, but didn't know that our forebears had struggled over the same themes. Doesn't the late 20th century debate about micro and macroevolution raise the same questions about different causes at higher and lower taxonomic levels (the basis of Goldschmidt's argument, for example — see pp. 451–466); and don't extrapolationists still charge the defenders of higher level causality with proposing untestable theories of evolutionary change?
I do not find this persistence surprisin
g at all (see Gould, 1977a). I have already cited (p. 58) A. N. Whitehead's famous remark that all later philosophy is a footnote to Plato. He did not mean to argue, by this statement, that no one (including himself) had thought anything new for more than two thousand years. Rather, he wished to defend the proposition that truly deep issues are few and not o obscure. The first great thinker should be able to lay out a framework and specify the primary questions. Later history must recycle the same issues, while offering new explanations in abundance (especially in empirical realms where truly novel information becomes available). Lamarck, for all his stubbornness and for all the idiosyncrasies of his theory, was a great thinker, and he did find a location for all major questions within his system. His theory therefore becomes a starting point, and later debate must engage the same issues. Given the central theorem of this book, I am especially gratified that Lamarck based the initiating system of our profession upon a theory of hierarchy — in a form that did not work, based on causes that we must reject for Darwin's good reasons; but a theory of hierarchy nonetheless. Evolutionary theory therefore set its roots, and cut its teeth, in the concept of hierarchical levels of causality.
An Interlude on Darwin's Reaction
In the flood of Darwinian scholarship unleashed after the centennial celebrations of 1959 and continuing unabated today, I regard no reform as more important than the thorough debunking of the romantic myth that Darwin, alone and at sea, separated from the constraints of his culture, apprehended evolution as an objective raw truth of nature. This Galapagos myth, rooted in tortoises and finches, is demonstrably false in Darwin's particular case, and surely bankrupt as a general statement about human psychology and the sociology of knowledge.
The Structure of Evolutionary Theory Page 32