The Structure of Evolutionary Theory

by Stephen Jay Gould

  5-3. Hyatt combined his concept of a predetermined phyletic life cycle with his principle of universal acceleration to explain how even the simplified ontogenies of regressive evolution can originate by acceleration. In Hyatt's “old age theory” (his designation) as extinction nears; senile stages of phyletic youth and maturity become the adult stages of a waning stock in racial senescence. Ontogeny be­comes so shortened by acceleration and deletion that senile stages merge with persistent juvenile stages to produce a greatly simplified and senile course of life. From Gould, 1977b.

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  combined with geratologous characteristics; secondly, the earlier develop­ment of geratologous characteristics and their fusion with larval characteris­tics, which occasions the complete replacement of progressive characters, and occurs only in the extreme forms of retrogressive series.”

  Hyatt applied his old-age theory with abandon to all spheres of life and culture. I find no usage more curious than his invocation of phylogerontism to argue against voting for women (1897b). Hyatt claims that “in the early history of mankind the women and men led lives more nearly alike and were consequently more alike physically and mentally, than they have become sub­sequently in the history of highly civilized peoples. This divergence of the sexes is a marked characteristic of progression among highly civilized races.” Ontogenetic old age tends to blur sexual differences as men become less hir­sute and develops larger breasts, while sexual activity declines equally (or so Hyatt claimed) in both sexes. Since phyletic sequences mirror ontogeny (and since the human race has become dangerously phylogerontic already), we must beware any culturally enhanced blurring of distinctions between the sexes — for androgyny of any form (physical, cultural or conceptual) denotes racial senescence. Giving the vote to women will enhance this dangerous ten­dency towards equalization of roles:

  Such changes [women's suffrage] . . . might lead to what we might now consider as intellectual advance, [but] this would not in any way alter the facts that women would be tending to become virified and men to be­come effeminized, and both would have, therefore, entered upon the ret­rogressive period of their evolution . . . The danger to women cannot be exaggerated, nor too carefully considered, in view of the fact that ad­vanced women have adopted the standard of men, and have not tried as yet to originate feminine ideals to guide them in their new careers and thus maintain the divergence of the sexes (1897, p. 91).

  This notion of an internal program for phylogeny (including the time bomb of inherent racial senescence and extinction) ran so contrary to Darwin's con­victions about functionalism and contingency that he couldn't grasp Hyatt's conception at all (more, I think, through disbelief at the content, than inabil­ity to comprehend the argument). In 1872, as Darwin grappled with views of the American school in preparing the 6th and last edition of the Origin, he engaged Hyatt in a long correspondence about acceleration and racial life cy­cles (in F. Darwin, 1903, pp. 338-348). Darwin expressed his perplexity in the first letter: “I confess that I have never been able to grasp fully what you [that is, Cope and Hyatt] wish to show, and I presume that this must be ow­ing to some dulness on my part” (in F. Darwin, 1903, p. 339).

  After several exchanges of letters and diagrams (with some gain in clarification), Darwin remained puzzled by the most anti-selectionist and non-functionalist theme in Hyatt's system: the explanation of simplified ontogenies in phyletic old age by intensified acceleration, with senile adult features in­terpreted as nonadaptive preludes to extinction. Darwin conjectured in response: [Page 373] why not propose the far simpler interpretation that these shortened ontogenies and “degraded” adult forms represent adaptations to conditions of life that also characterized early stages of the lineage. This stark contrast and mutual incomprehension illustrate, in a striking manner, the difference between Hyatt's formalist orthogenesis as an ultimate drive to phyletic death, and Darwin's functionalism, with extinction as failure to adapt. Darwin wrote to Hyatt (in F. Darwin, 1903, pp. 343-344): “With respect to degrada­tion of species towards the close of a series, I have nothing to say, except that before I arrived at the end of your letter, it occurred to me that the earlier and simpler ammonites must have been well adapted to their conditions, and that when the species were verging towards extinction (owing probably to the presence of some more successful competitors) they would naturally become readapted to simpler conditions.”

  Later in the same letter, Darwin pens the most famous line of this correspondence — a lovely contrast between the contingency of environmentally entrained adaptation and the predictability of “hardline” formalism as a the­ory of internal necessity: “After long reflection I cannot avoid the conviction that no innate tendency to progressive development exists” (in F. Darwin, 1903, volume 1, p. 344).

  Through the density of theoretical discussion in these letters, another theme circulates. Hyatt expresses his plans to restudy one of the most famous paleontological series of presumed stratigraphic continuity in an isolated set­ting: the Miocene fresh-water planorbid pulmonates of the Steinheim lake in Germany (then interpreted as a volcanic caldera, but now recognized as a meteor crater — see Reif, 1976). The German paleontologist Hilgendorf had published an already classical account in 1866, including one of the first ge­nealogical diagrams to reflect Darwin's new world order. Hyatt proposed a restudy and Darwin opined: “I earnestly hope that you may visit Hilgendorf's famous deposit ... I most sincerely wish you success in your valuable and difficult researches” (in F. Darwin, 1903, p. 344). Hyatt proceeded, and even­tually provoked Darwin's last and bitter response to his orthogenetic ideas by sending Darwin a copy of his monograph (1880) on the Steinheim planorbids.

  Hyatt's proposed phylogeny could hardly differ more from Hilgendorf's original interpretation (Fig. 5-4). Where Hilgendorf drew a conventional branching tree with a monophyletic root, Hyatt presented four lineages, sepa­rate at the base and evolving in strict parallel. Such a striking difference should, in our conventional view of scientific change, record Hyatt's im­proved observations at the site. Hyatt did make some empirical changes (al­though we would have to view his effort, in retrospect, as a continuity in steady state rather than an improvement over Hilgendorf, for he corrected some errors but introduced just as many others). But Hyatt's alterations pri­marily record the application of a different theory to the same data. Iconogra­phy often provides a powerful guide to conceptual frameworks because pic­tures frequently make explicit what our psyches fail to acknowledge in the [Page 374] verbal mode (Rudwick, 1992; Gould, 1989c, 1993d, 1996a). Hyatt's phylogeny of the Steinheim planorbids (Fig. 5-5) epitomizes hardline orthogenesis under the guidance of phyletic life cycles.

  Hyatt depicts four lineages within the lakebeds, each beginning from an ancestral Planorbis levis stock (not shown). This putative phylogeny rests upon two principles derived from his orthogenetic “old age” theory (and showing that Hyatt's convictions directed his observations, rather than the conventionally touted vice versa).

  1. Hyatt distinguished the four lineages on the basis of supposedly progres­sive and retrogressive characters. The rationale for these designations proba­bly owed more to vague and general cultural conventions (largely the folklore of more and less as better and worse) than to any explicitly biological argu­ment. Progressive characters include increase in size, shell thickness, strength of ornamentation, and change of shape from planispiral (flat like an am­monite) to trochiform (domed like a conventional snail). In other words, small, thin, smooth, and flat specifies a primitive state; whereas large, thick,

  5-4. Hilgendorf's original interpretation of 1866 for the evolution of the Steinheim planorbids. Note how Hilgendorf depicts his phylogeny in a convetionally tree-like form.

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  5-5. Hyatt's phylogeny for the Steinheim planorbids could not differ more from Hilgendorf's. Hyatt envisages several parallel lineages each in different stages of the same phyletic life cycle, with some lineages becoming stronger (as expresse
d in their larger and thicker shells) and others becoming evolutionarily senile in their thinner, smaller, and irregularly coiled shells. This interesting figure comes from a glass plate that Hyatt prepared for his 1880 monograph but did not pub­lish. The printed version is much cruder and less informative. I here publish Hyatt's original for the first time. (I now occupy his office and I found this plate in the drawer that still contains his Steinheim specimens.) The three rightmost lineages represent three sub lines of a single degenerating stock, hence giving four lineages in toto (as the text states).

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  bumpy and blocky equals advanced. By contrast, regressive characters in­clude decrease in size, loss of ornamentation, thinning of the shell and, above all, a tendency for irregular growth by uncoiling (loss of order as a sign of both ontogenetic and phyletic senility).

  Hyatt identifies three of his four lineages as progressive, distinguishing them by different combinations of the key characters. The most purely pro­gressive steinheimensis-trochiformis lineage advances by all criteria to greater size, thickness, and quadrate shape with keels and carinae (rather than a smooth whorl profile) and, as the formal name states, a domed outline. Shells of the oxystomus-supremus lineage become larger and more ornamented; the spire does not increase in height, but the shell still grows taller because the under­side of the whorl profile becomes more inflated. The parvus-crescens lineage shows less advance, as the shell remains flat and smooth, but increase in size establishes the primarily progressive character.

  Retrogressive tendencies appear in the three sublineages of the remaining branch, all derived from P. minutus. The turbinatus sublineage shows a mix­ture of progressive and retrogressive characters (Hyatt, 1880, p. 17, refers to this melding as “the battle of the tendencies”), with modest size increase and some strengthening of ornament offsetting a basic decline. The middle, or denudatus, sublineage is purely retrogressive, as shells become smaller, smoother and irregular in growth by increasingly erratic coiling. Finally, the distortus lineage also mixes phyletic strength and weakness. Ornament re­mains strong and size increases in portions of the lineage; but, as the name implies, coiling becomes irregular as the stock declines.

  2. Although later convention (and emerging practice in his own time) would lead us to read Hyatt's chart as a stratigraphic sequence, his phylogeny employs an unconventional iconography. Vertical position does not represent time or stratigraphy, but rather stage in an orthogenetic sequence. Snails drawn at the same level did not necessarily live at the same time, but show common “attainment” in a phyletic series. Thus, for example, P. trochifortnis, the ultimate stage of the most progressive series, lived near the bottom of the stratigraphic sequence — implying that this lineage ran its full course with geological rapidity at the base of the section. Conversely, P. oxystomus, the initial form of the second progressive lineage, makes an initial appearance high in the sequence.

  This unconventional iconography illustrates the power of theory to chan­nel perception — orthogenesis as an organizing principle, in this specific case. Consider the immense confidence that a scientist must be willing to invest in the validity of a chosen surrogate to substitute any other criterion for the emi­nently available (and obviously meaningful) stratigraphic order of time as the measuring rod for vertical position in phyletic charts. (Cladists have created quite a fuss in our day by using inferred branching order in preference to time of observed paleontological appearance, if they include fossils in their phylogenies at all — see Schaeffer, Hecht, and Eldredge, 1972. In the heyday of overweening confidence in recapitulation, several paleontologists reversed the conventional geological procedure and inferred stratigraphic order from [Page 377] presumed phyletic stage based on ontogenetic repetition of ancestral adult stages — see Smith, 1898, on ammonite phylogeny, for example. Thus, Hyatt's procedure, while interestingly unconventional, scarcely lacks precedent — or consequent.)

  In sum, Hyatt presents a picture of multiple lineages, evolving in parallel but at different times (though in the same lake), through a preset sequence of stages — with some lineages displaying an upward march to progressive char­acters, and others a downward slide to regressive states of the same features. Hyatt justifies all these claims under his old-age theory of orthogenetic un­folding: phylogenies proceed inexorably from periods of phyletic youth and vigor, through maturity to racial senescence and extinction. Consider a series of questions, all resolved by the orthogenetic interpretation (and all refuting Darwinism, or any other functional account):

  1. Why do the separate lineages go through similar stages? The causes cannot reside in functional entrainment by common environmental pressures (either by Darwinian selection or Lamarckian response to perceived needs) because the same stages occur at different times in various lineages (same re­sponse in different environments), while different lineages (progressive vs. re­gressive) often evolve disparate forms at the same time (different response in the same environment). Hyatt argues that the cause of parallelism must there­fore be sought in an internal shove, not an external (environmental) push:

  While the perpetuation and survival of the differential characteristics can be thus accounted for [by natural selection], we must look to other causes for the production of the parallel forms and the regularity of suc­cession of these forms, as shown in the arrangement in the different se­ries, and in the development of the individual. This cause lies in some law of growth and heredity which reacts against the tendency of the physical environment to produce variations and differences, and pro­duces parallelism in the development of different individuals of the same species, of different species in the same series, and in the succession of forms in the different series, and also limits the tendency to variation within definite boundaries in the species (1880, p. 26).

  2. Why does the invariant series of stages follow this characteristic se­quence, with either a march to progressive features in shell size, thickness, shape and coiling, or a fall to increasingly degenerate states of the same char­acters? Again, an answer cannot be provided by functional adaptation in ei­ther the Darwinian or Lamarckian mode, for extended regressive sequences, by their inadaptive nature, could not then occur. Instead, this sequence of up and down marks the full scope of the “grand potential ontogeny,” defining the orthogenetic phylogeny of the entire fauna: “Thus, we can readily under­stand that each of these series, whether progressive or retrogressive, can so far as its collective life is concerned, be compared in the closest manner with the life of an individual, and similar correspondence be traced in both, and also that the tendencies exhibited are of two kinds in each, one towards [Page 378] building up of the organization and the other directly opposed to this” (1880, pp. 17-18).

  Hyatt also tries to provide direct evidence for the ontogenetic construction of phylogeny. He notes, for example, that ordinary adults of regressive lin­eages reach stages found only in the most degenerate individuals of progres­sive populations — those that have grown far past their normal adult form to a marked senility. The ruinous dotage of a progressive individual therefore corresponds with the ordinary adult form of a phylogerontic race (1880, p. 17).

  3. Why, in the same lake and during the same general period, do some lineages progress while other closely related lines regress? Again, no functional or adaptationist answer can suffice, for the same times and environments should not engender opposite responses in such closely allied lineages. The solution must reside in internal orthogenesis. Lineages progress or regress ac­cording to their internal state — particularly, their status in the unrolling of the grand potential ontogeny. Progressive lineages, in their phyletic youth, can re­sist a harsh environment; but regressive sequences, in their phyletic dotage, must succumb. Hyatt's four lineages achieve their distinctions by occupying different positions in the grand potential ontogeny. His three progressive lin­eages evolve in the vigor of their phyletic youth or maturity; meanwhile, the regressive series decline in their phylogerontic senil
ity.

  Environment does not, as in functionalist theories, operate as an aid or entrainer, but rather as a clear detriment and degrading force. Lineages in their phyletic youth can prevail by innate virility against the incessant storm:

  How shall we account for the progression of the progressive series? How then could this environment act upon such closely allied shells, in such an opposite way as to cause the decrease of some races and be entirely healthy for others? We habitually refer such questions among animals, and in man, to the innate strength or pliability of the constitution of the race or the individual, and account for the survival, growth, and devel­opment of races and individuals by this reference to their supposed abil­ity either to resist change in their surroundings, or to become modified in accordance therewith ... Precisely the same environment, therefore, may produce results diametrically opposed to each other, even upon different individuals of the same species or closely allied forms, provided there is anything in the constitution either directly acquired or inherited, which enables the organization of one to resist or fit itself to conditions which the other cannot healthfully endure (1880, p. 16).