(Linguistic choices can be highly illuminating. Note how Eimer refers to adaptation as a “stress” rather than a determining cause — that is, a push from the outside that can, at most, speed up, slow down, or change in minor ways the primary pathway of internal direction.)
Second, although adaptationist guesses can be formulated for the observed channels, formalist alternatives also exist, and seem eminently more reasonable. The law of undulation from back to front, for example, only reflects the metameric growth of many animals. The back segments form last, and late stages, under the biogenetic law, develop progressive characters (1890, pp. 60, 69).
In sum, orthogenesis derails Darwinian functionalism by denying the crucial requirement for undirected variability. “The variation of species takes place not in all kinds of directions irregularly, but always in definite directions, and indeed in each species in a given time in only a few directions” (1890, p. 20). Ultimately, Eimer rejected Darwinism for the most common of all 19th century reasons — the critique of “creativity” — for he clearly understood the deathblow that such powerfully channeled and limited variation would deal to Darwinian hopes for awarding a dominant relative frequency to natural selection in creating evolutionary change: “Natural selection becomes weak [ohnmdchtig] thereby. It cannot be depicted as an active major cause [Hauptmittel] in the transformation of forms; at most, it can be an auxiliary cause [Nebenmittel] of such transformation, as it can only perfect what orthogenesis ordains” (1897, pp. 14-15).
The metaphors and images chosen by scientists to illustrate their complex views often provide our best insight into their relative weighting of interacting forces and foci. Eimer developed what he and others considered a “liberal” or a “compromise” version of orthogenesis, where internal forces of directed variation do not determine the entire shape and rate of phylogeny (as in Hyatt's more extreme views), but rather work in balance with environmental determinants — a model of external triggers and choosers for a strictly limited number of internally set pathways. This balanced view, as noted above, might have awarded important space to Darwinian functionalism as an external force — except for Eimer's particular commitment to Lamarckian causes as primary determinants of the external component, with selection acting only as an auxiliary force, largely confined to the negative role of eliminating the unfit.
Eimer summarized these weightings in a metaphor that compared evolution with the migration of a population. The direction of movement represents the orthogenetic pathway, the dominant cause of the entire process. External forces of environment act primarily in finetuning this predetermined direction. Adaptation may play an important role, but the Lamarckian inheritance of acquired characters trumps Darwinian factors in this realm of functional [Page 365] influence. Selection only sharpens the edge of success by eliminating the failures.
Thus we may compare the whole process of the modification of forms to the results of the migration of the people over an extensive foreign territory. Some tribes, not having the strength to follow, soon, others later, remain behind; others again reach a distant goal. Some retain their characters in their new home or strengthen them, even modify them by correlation, others change under the influence of external conditions and adapt themselves to the environment — all that is not sufficiently capable of endurance is left lying by the way and perishes, and if the struggle for existence is at all severe only the toughest of all survive (1890, p. 55).
ALPHEUS HYATT: AN ORTHOGENETIC HARD LINE FROM
THE WORLD OF MOLLUSKS
Standard examples of orthogenesis all took the same form: paleontologically based, and therefore temporally extensive, monotonic trends towards clearly inadaptive features, leading inevitably to the extinction of the afflicted lineage. Supposed “best cases” included the enlarging antlers of the “Irish Elk” (but see Gould, 1974), the extended canines of saber-toothed cats, and the self-strangulation of the oyster Gryphaea, as overcoiling of one valve clamped the other shut, immuring the animal in its own shell (but see Gould, 1972).
These lurid stories, in their textbook versions, are the caricatures of a serious non-Darwinian theory once quite popular among paleontologists from the late 19th century through the 1930's: the idea that trends, though adaptively initiated, might break from environmental control and run, inexorably along the same path, eventually to extinction — if the proximal cause that originally responded to the adaptive pressure became so entrenched that selection could no longer halt or reverse the trend. W. D. Lang (1923), for example, proposed that an originally adaptive increase in rates of shell secretion might become unreversible, leading to Gryphaea's deathly dilemma: “These trends, even if at first encouraged by the environment because they are of use to the organism, are soon out of the environment's control; they are lapses which may overtake Ostrea [the supposed ancestor of Gryphaea] at any moment of its evolution — trends which having once started continue inevitably to the point when their exaggeration puts the organism so much out of harmony with its environment as to cause its extinction.” A. E. Trueman, who had developed the empirical case for Gryphaea (1922), also asserted the anti-Darwinian character of internally driven trends: “Excessive development implies that the evolution was out of the control of the environment and it may be presumed that some internal factor was responsible” (1940, p. 93). Trueman proposed no mystical or vitalist explanation (as the standard caricature maintains), but sought a cause consistent with modern genetics. (He suggested [Page 366] that such inadaptive orthogenesis might arise by mutation pressure too high for natural selection to overcome.)
An even stronger anti-Darwinian version of the theory — a maximal departure from functionalist explanation — held that all stages of a trend might follow a prefigured, internally programmed path, and that environmental selection need not be invoked at all, even for an initiating push. These versions usually anchored their argument in a more than metaphorical reading of phylogeny as akin to ontogeny and imbued with similar, inevitable stages of youth, maturity and old age.
To illustrate this hardest-line account of orthogenesis (and to set up a contrast with the opposite and most accommodating version of C. O. Whitman, discussed in the next section), I turn to an influential monograph on Miocene snails (see, for example, the lengthy popular and well illustrated account in Le Conte, 1888, pp. 236-239), published in 1880 by the American paleontologist Alpheus Hyatt. The case becomes particularly relevant for this historical chapter because Darwin and Hyatt had engaged in a long and frustrating correspondence, full of misunderstanding, about the theory of ontogenetically programmed phylogeny (see F. Darwin, 1903, pp. 338-348). Hyatt later sent Darwin a copy of his 1880 monograph, and Darwin replied, less than a year before his death, with an uncharacteristically ungracious acknowledgment (reprinted in F. Darwin, 1903, p. 393 — letter of May 8, 1881): “I am much obliged for your kind gift... which I shall be glad to read, as the case has always seemed to me a very curious one. It is all the kinder in you to send me this book, as I am aware that you think that I have done nothing to advance the good cause of the Descent-theory.”
Hyatt, deeply stung, donned his hair shirt, and quickly penned a response on May 23: “I tell you that your strongest supporters can hardly give you greater esteem and honor. I have striven to get a just idea of your theory, but no doubt have failed to convey this in my publications as it ought to be done.” Francis Darwin, Charles' son and editor of this volume, then adds, after quoting Hyatt: “We find other equally strong and genuine expressions of respect in Prof. Hyatt's letters.” But, genuine respect notwithstanding — and I don't doubt Hyatt's bonae fides for a moment — no version of orthogenesis could be more contrary to Darwinism than the theory of internally programmed phylogeny.
From a parochial American standpoint at least, the evolutionary theories devised and promoted by paleontologists E. D. Cope and Alpheus Hyatt occupy an important historical position. For a nation st
ill coming of age as a scientific power, and still bearing a reputation, at least in natural history, as supplier of data to the theory-mills of a more sophisticated Europe, the rise of an American movement, centered in a novel theoretical perspective, and gaining both attention and respect in Europe, marked an important gain in maturity. Cope and Hyatt led this co-called “American school,” often identified as “Neo-Lamarckism.”
Cope and Hyatt did accept the inheritance of acquired characters, but a new view on the mechanism of recapitulation, and a distinctive argument about ontogeny in general, built the truly central and characteristic argument [Page 367] of their theory (see Gould, 1977b, Chapter 4). These two scientists proposed a new mechanics for the biogenetic law, and this “principle of acceleration” forms the core of their theory and the basis of its orthogenetic implications. Ontogeny will recapitulate phylogeny provided that two necessary principles can be validated. All supporters of the biogenetic law promoted some version of these principles. First, new characters must arise in phylogeny as additions to the end of previous ontogenies. This principle of “terminal addition” (Gould, 1977b) would, of itself, engender recapitulation, as descendants pass through the adult stages of ancestors before accreting their own novelties in ontogeny — except for a logical problem that required the second principle for a full and coherent theory. The phylogeny of a lineage unfolds through thousands of steps in geological immensity; new stages cannot be added indefinitely to the unaltered ends of previous ontogenies, lest growth to adulthood take untold years to reach completion. Some process — some law of heredity — must produce a general speeding-up of development, so that ancestral ontogenies can unfold more rapidly, leaving time at the end for addition of novel features.
All recapitulationists necessarily defended some form of speeding up for ancestral ontogenies through phyletic time. Haeckel himself, who thought a great deal about genealogies but precious little about mechanisms, advocated a differential dropping out of stages, with compression of the remaining steps to a shortened ancestral ontogeny (Gould, 1977b). Cope and Hyatt, who both devised a theory of recapitulation in 1866 (independently of each other and of Haeckel), first proposed an ultimately more popular and plausible version of ontogenetic quickening — the “principle of acceleration,” or general increase in rate of development (with no necessary excision of stages). This law of acceleration (as a foundation for recapitulation) became the most important theoretical contribution of the American school (Fig. 5-2).
The law of acceleration held that ancestral ontogenies unroll more and more rapidly in successive descendants, thus making room for new stages in phylogeny. (The gill slits of a human embryo can therefore represent the compressed and accelerated adult form of our piscine ancestry.) With ontogeny thus depicted as a quickening treadmill through time, attention could shift to the nature of stages that accumulated in successive terminal additions — for the accreted stages form a series that defines the lineage's phylogeny. If the sequence of accreted stages represents the unfolding of an internal “program,” then phylogeny can be justly called orthogenetic — for the law of acceleration makes room on the treadmill, and the next stage of a predictable sequence then struts its hour upon the adult stage.
Later versions of “Neo-Lamarckism” in this American style cannot be called orthogenetic because they did not propose an internally programmed series of new stages. These later accounts embody a view of causality every bit as functionalist as Darwin's, though relying upon Lamarckian mechanisms rather than natural selection. New features arise adaptively as organisms actively respond to needs imposed by altered environments. The sequence of novel stages accretes as a contingent series, mapping the functional requirements of a changing external world.
[Page 368]
5-2. Mechanisms proposed by recapitulationists to compress late stages of an ancestral ontogeny into earlier stages of the embryology of descendants. In Cope and Hyatt's solution, shown bottom left at B, stages are compressed by acceleration. In Haeckel's solution, bottom right at C, some stages are simply omitted by deletion. From Gould, 1977b.
But earlier versions of Cope's views (and Hyatt's opinion throughout his life) posit an evolutionary mechanism diametrically opposed to this later functionalism — an internal dynamic yielding an orthogenetic phylogeny of predetermined stages, with the source of predictable novelty inherent in ontogeny itself. This history of lineages unfolds along a “grand potential ontogeny” much longer than the realized portion of early species in a phyletic series. The adult stage of the initiating species does not reach beyond an early phase of the potential sequence. (Suppose, for example, that the full series includes 100 stages, ending in predictable extinction. The ancestral species may only progress from stages 1 to 10 in its own ontogeny, leaving 90 available steps for successive terminal additions in the phylogeny of subsequent species.) This concept of an extended potential ontogeny as the source of predictable phyletic additions became the most powerful version within a class of non-Darwinian theories generally regarded today as purely fanciful or falsely analogic, and without conceivable mechanism — the idea of racial ontogenies and life cycles. But the concept of a genealogical ontogeny, however indefensible by modern standards, once possessed an interesting rationale in this recapitulatory context.* [Page 369]
In Cope's early view, lineages arose with a latent phyletic life cycle extending far beyond an initially realized ontogeny. So long as acceleration prevailed in phylogeny, old ontogenies unfolded more rapidly and new stages of the grand potential ontogeny accreted at the end. A much less common form of regressive evolution could foster a slowing down of ontogeny (“retardation” in Cope's terminology) and retention of previously juvenile stages as adult forms of descendants (the older “degenerative” interpretation of a phenomenon now generally viewed more positively as “neoteny”). Since acceleration occurs far more commonly than retardation in evolution (as progress generally prevails over regress), the general vector of genealogy proceeds as an unrolling of phyletic life cycles. The stages of phylogeny are, in any case, internally programmed and predictable. Cope wrote in 1869 (quoted in Cope, 1887, p. 123): “Genera have been produced by a system of retardation or acceleration in the development of individuals: the former on pre-established, the latter on preconceived lines of direction.”* Cope recognized the formalist implication of this view, as expressed in the key postulate that the origin of a structure precedes its use — in opposition to the cardinal principle of any functionalist theory (including both Darwinism and Lamarckism) that functional [Page 370] needs impel adaptive change. (Cope's subsequent shift to a functionalist position prompted the development of his later Neo-Lamarckism.) Cope wrote in 1870 (quoted in Cope, 1887, pp. 145-146): “We look upon progress as the result of the expenditure of some force forearranged for that end. It may become, then, a question whether in characters of high grade the habit or use is not rather the result of the acquisition of the structure than the structure the result of the encouragement it offered to its assumed beginnings by its use.”
Hyatt differed from Cope in an essential manner that made his theory the most uncompromisingly recapitulatory of all 19th century views, the most committed of all proposed evolutionary mechanics to “programmed” racial life cycles, and the most orthogenetic. Cope had provided the obvious interpretation for a standard 19th century perception that, whereas most lineages progressed by complexification, others regressed to greater simplicity. Cope argued that progressive lineages undergo acceleration and therefore “gain room” to add new stages to the end of old ontogenies; regressive lineages, on the other hand, experience ontogenetic retardation and never surpass the juvenile stages of their ancestry. Hyatt, in a paradox resolved by an ingenious argument, tried to render both progressive and regressive evolution as results of acceleration alone. For Hyatt, the law of acceleration reigned virtually without exception; no more extensive or uncompromising version of universal reca
pitulation has ever been offered.
Hyatt resolved the apparent paradox with an argument that he affectionately called his “old age theory.” The programmed steps of a potential phylogeny proceed through a sequence more than merely analogous to the phases of ontogeny. Adult stages of early species in a lineage exhibit traits of phyletic youth; adults in a lineage's geological midlife display the features of phyletic maturity; while adults of species near the extinction of a lineage finally develop unmistakable signs of phyletic senility. Hyatt's hardest-line, internally programmed version of orthogenesis rests upon this notion of a phyletic life cycle. The stages of a phylogeny become as predictable and predetermined as the phases of an ontogenetic sequence. Environment must be sufficiently favorable to permit the unfolding (just as a fetus will not grow without adequate nutrition), but the sequence of stages is internally ordained, not functionally entrained by interaction with a surrounding environment. Hyatt wrote (1897, pp. 91-92): “There is a rise of the individual through progressive stages of development to the adult and a decline through old age to extinction. In the evolution of the stock to which the individual belongs there is a similar law, a rise through progressive stages of evolution to an acme and a decline through retrogressive stages to extinction . . . The type, like the individual, has only a limited store of vitality, and both must progress and retrogress, complete a cycle and finally die out, in obedience to the same law.”
In this scheme, even the simplified ontogenies of regressive evolution can arise by acceleration (see Fig. 5-3). The adult stages of phyletic old age resemble, by analogy to the “second childhood” of our own senility, the simple features of youth (although these recurring traits signify decline and extinction, rather than exuberance, as they now appear in an exhausted stock). By this [Page 371] time, acceleration has become so intense that most middle stages in ontogeny begin to drop out entirely. The earliest embryonic stages, however, remain stubbornly persistent. As acceleration intensifies, newly introduced senile features push back the older progressive traits of phyletic midlife, until these middle stages encounter the persistent juvenile features. Pushed at one end by senile features, and pressed against the impenetrable wall of persistent embryonic traits at the other end, these progressive middle stages finally tumble off the phyletic conveyor belt. Characters of phyletic old age now merge with juvenile features (see Fig. 5-3). Ontogeny becomes shorter (by excision of intermediate stages), and simpler (because the remaining juvenile and old-age stages resemble each other in external appearance). In this way, the simplified ontogeny of regressive lineages does not represent retardation or truncation of development, but rather acceleration so intense that all intermediate complexity (once intercalated between true youth and “second childhood”) disappears by compression. Hyatt writes (1889, p. x): “Acceleration produces first, the earlier development of some of the progressive characteristics
The Structure of Evolutionary Theory Page 59
