Weismann explicitly identified this inherent and automatic synergism as a major insight, and a logical completion of his argument for the Allmacht of selection. Noting “the harmony of the direction of variation with the requirements of the conditions of life” (1896, p. 38), Weismann continues: “The degree of adaptiveness which a part possesses itself evokes the direction of variation of that part. This proposition seems to me to round off the whole theory of selection and to give to it that degree of inner perfection and completeness which is necessary to protect it against the many doubts which have gathered around it on all sides like so many lowering thunderclouds . . . The principal and fundamental objection that selection is unable to create the variations with which it works, is removed by the apprehension that a germinal selection exists.” And, more succinctly for the centennial of Darwin's birth, Weismann reduced this theme to a celebratory aphorism (1909, p. 39): “Germinal selection supplies the stones out of which personal selection builds her temples and palaces: adaptations” — thus amalgamating the synergistic link of levels, the Allmacht of selection, and the primacy of adaptation (as recorded in a metaphorical linkage with the noblest of buildings, both spiritual and temporal).
GERMINAL SELECTION AS A FULL THEORY OF HIERARCHY
Weismann had granted an important role to germinal selection in his initial formulation, but he had not yet developed a full theory of hierarchy, for germinal selection could only walk the same paths established by ordinary natural selection — at most accelerating or intensifying the journey. But when Weismann wrote the major book and summation of his later career, Vortrage iiber Descendenztheorie (1902; English translation, 1903), he devoted two full chapters to germinal selection and, without explicitly acknowledging the [Page 220] change or extension, radically altered his conception into a full selectionist theory of hierarchy, the first such proposal in the history of evolutionary thought.
Taking an opposite tack from his original formulation, Weismann now proposed to define the scope of germinal selection by what such a process could accomplish without and beyond organismal selection: “We shall attempt to gain clearness as to what it can do, and how far the sphere of its influence extends, and, in particular, whether it can effect lasting transformations of species without the cooperation of personal selection, and what kind of variations we may ascribe to it alone” (1903, vol. 2, p. 126).
Weismann now recognized that he could use germinal selection to escape the straitjacket of Panglossian adaptation. He could finally admit the non-adaptive character of some phenotypic features without straying from the Allmacht of selection, or giving comfort to Lamarckism — for traits arising by germinal selection may be neutral or even harmful to survival in the Darwinian world of competition among organisms. Weismann recognized two classes of nonadaptive features potentially ascribable to germinal selection.
Neutral features of small or no importance. Since germinal selection can promote changes invisible to organismal selection, Weismann wondered whether such minor variations as human racial differences — attributed by Darwin to sexual selection based on disparate standards of beauty arising for capricious reasons in various societies — might actually arise as effects of germinal selection: “It cannot be denied that there are characters which have no special biological significance [although] ... it is difficult and often impossible to point these out with certainty. The shape of the human nose and the human ear, the color of the hair and the iris, may be such indifferent characters whose peculiarities are to be referred solely to germinal selection” (1903, vol. 2, p. 134).
Orthogenetic drives that may yield harmful features and even lead to extinction. In a remarkable departure from the almost strident panselectionism of his earlier years, Weismann now approved certain claims for orthogenesis, and admitted the existence of harmful trends (based on directionality in variation) that organismal selection could not reverse. He even accepted the classic examples of the anti-Darwinian schools as orthogenetic and harmful prima facie — the antlers of Irish Elks, and the massive canines of saber-toothed cats (1903, vol. 2, p. 139). He embraced the best cases of his opponents because germinal selection — once he reversed his original view and grasped its power to work against organismal selection — could convert these enemy troops to the doctrine of Allmacht. For when germinal selection acts with sufficient power, then all the determinants favored by organismal selection may be eliminated entirely, leaving only the vigorous determinants of harmful orthogenetic features, and rendering conventional selection impotent for lack of raw material: “In this case the variation-direction which had gained the mastery in all ids could no longer be sufficiently held in check by personal selection, because the variations in the contrary direction would be much too slight to attain to selective value” (1903, vol. 2, p. 139). [Page 221]
Following the early 20th century vogue for eugenics, Weismann used this argument to promote a positive program of breeding to save the human race. Germinal selection must be responsible for any decline of the human stock engendered by relaxation of natural selection — for panmixia lacks sufficient strength to produce such an effect, while Lamarckian inheritance does not exist. This orthogenetic deterioration by germinal selection can only be reversed by a reimposition of Darwinian competition in the organismal mode, with reproductive success to the victors. Arguing that military service might operate as a good filter for identifying bodies well suited for success in organismal selection, Weismann suggested (1903, vol. 2, p. 147): “It would indeed be well if only those who had gone through a term of military service were allowed to beget children” (thus adding another example to the compendium of social nonsense advanced by prominent evolutionists in the name of Darwinism — see Chapter 7, and Fisher, 1930).
But, far more important than merely extending the domain of germinal selection to explain potentially nonadaptive organismal traits, Weismann also enlarged the conceptual realm of levels in selection from a narrow mechanism for synergism to a full theory of hierarchy. Weismann had now worked his way through the logic of multi-level selection theory, and had recognized the two key ingredients of any full account.
Independence of levels and potential for conflict. The attribution of orthogenesis to germinal selection implies that suborganismal selection can act separately from conventional Darwinian selection, and even work in a contrary direction to decrease phenotypic adaptation. Thus, the process that Weismann had originally promoted to make natural selection even more effective had become, by honest probing into all corners and implications of the argument, a separate cause that could work either with or against the canonical Darwinian mode. In fact, Weismann now argued that potential independence from the Darwinian level of organismal selection establishes the primary significance for germinal selection in evolutionary theory (1903, vol. 2, p. 119): “In this fact lies the great importance of this play of forces within the germ-plasm, that it gives rise to variations quite independently of the relations of the organism to the external world. In many cases, of course, personal selection intervenes, but even then it cannot directly effect [sic, and correctly; he means 'cause,' not just 'affect'] the rising or falling of the individual determinants — these are processes quite outside of its influence.”
In his most revealing change, Weismann even reinterprets his type case of degeneration. He had previously tried to explain degeneration as a result of germinal selection completing a process that natural selection had started but could not finish. Now, without any change in evolutionary mechanics, he speaks of germinal selection working differently and independently. He even claims that degeneration offers the purest case for potential independence of levels — for germinal and organismal selection usually act together, thus rendering their individual contributions operationally inseparable. But we know that organismal selection has disappeared in the final stages of degeneration, and we can therefore observe the unsullied action of germinal selection alone! [Page 222] “In o
ne direction variation can be proved to go on without limit, and that is downwards, as is proved by the fact of the disappearance of disused organs, for here we have a variation-direction, which has been followed to its utmost limit, and which is completely independent of personal selection; it proceeds quite uninterfered with by personal selection, and is left entirely to itself” [Weismann's italics] (1903, vol. 2, p. 129). At England's major centennial celebration of Darwin's birth, Weismann presented an even stronger statement (1909, p. 38): “Useless organs are the only ones which are not helped to ascend again by personal selection, and therefore in their case alone can we form any idea of how the primary constitutents behave, when they are subject solely to intragerminal forces.”
Such independence of levels implies potential conflict, with stability achieved through balance, or by the victory of one level. Natural selection, as a powerful force operating directly on phenotypes, usually prevails in its own domain of visible form. If germinal selection weakens a useful organ, natural selection can intervene in an antagonistic mode (except in degeneration, where natural selection ceases to act, and germinal selection reigns unchecked). “If a struggle for food and space actually takes place, then every passive weakening must lead to a permanent condition of weakness and a lasting and irretrievable diminution in the size and strength of the primary constituent concerned, unless personal selection intervenes, and choosing out the strongest among these weakened primary constituents, raises them again to their former level. But this never happens when the organ has become useless” (1903, vol. 2, p. 122).
Similarly, if germinal selection initiates an orthogenetic trend, natural selection can impose a halt by eliminating organisms with traits exaggerated beyond utility, thereby removing their positive determinants from the germinal population. (This basic antagonism, Weismann finally concluded in his strongest recognition of potential conflict between levels, may be virtually omnipresent in nature, and therefore fundamental to evolution, because positive organismal selection almost always elicits an upward trend in determinants by Weismann's earlier argument for synergism. Most stable species may not be quiescent with respect to selection, but balanced by a policing of germinal selection with opportune removals based upon Darwinian organismal competition.) “In the majority of cases the self-regulation which is afforded by personal selection will be enough to force back an organ which is in the act of increasing out of due proportion to within its proper limits. The bearers of such excessively increased determinants succumb in the struggle for existence, and the determinants are thus removed from the genealogical lineage of the species” (1903, vol. 2, p. 130).
But germinal selection can also triumph, and such victories may not be infrequent in nature. All orthogenetic and nonadaptive traits may record the potency of suborganismal processes in conflicts between levels of selection: “All excessive or defective hereditary malformations may be referred to germinal selection alone, that is, to the long-continued progressive or regressive variation of particular determinant-groups in a majority of ids” (1903, vol. 2, p. 138). [Page 223]
Expansion of the hierarchy both up and down from a Darwinian focus on organisms. Weismann devised germinal selection as an ad hoc hypothesis to resolve his longstanding embarrassment over the problem of degeneration. In 1896, he applied selection throughout Haeckel's hierarchy of “individuals,” extending from cell constitutents to clonal colonies (1896, p. 42), and recognizing three primary levels — Darwin's conventional struggle for existence among organisms, Roux's histonal selection, and his own germinal selection.
But by 1903, in a statement that I regard as wonderfully prophetic of current concerns, Weismann had proceeded beyond his immediate theoretical needs to full generality. He had used germinal selection to break through the Allmacht of exclusivity for Darwin's level. But now he recognized the inexorable logic of a fully developed and extended theory of hierarchy — reaching right up to species selection at the top.
I have called these processes which are ceaselessly going on within the germ-plasm, Germinal Selection, because they are analogous to those processes of selection which we already know in connection with the larger vital units, cells, cell-groups and persons. If the germ-plasm be a system of determinants, then the same laws of struggle for existence in regard to food and multiplication must hold sway among its parts which hold sway between all systems of vital units — among the biophors which form the protoplasm of the cell-body, among the cells of tissue, among the tissues of an organ, among the organs themselves, as well as among the individuals of a species and between species which compete with one another (1903, vol. 2, p. 119).
If Weismann had presented this full elaboration of hierarchy only as a footnote, a flash of insight in a book devoted to other goals, I could not claim him as an intellectual forebear of our modern excitement. Good ideas originate in fair abundance, and we must look to development and application for our main criteria of sustained scientific worth. If Weismann had even devoted an isolated chapter to hierarchy, I would note his insight with praise, but grant him limited success for failing to recognize the power of this theme as an organizing framework for evolutionary mechanisms. But, in fact, Weismann did fully grasp the fundamental difference between classical Darwinism and the expanded theory of interacting levels of selection — and he regarded his exposition of hierarchy as both the central feature of his mature thinking, and the unifying concept of all evolution: “This extension of the principle of selection to all grades of vital units is the characteristic feature of my theories; it is to this idea that these lectures lead, and it is this — in my own opinion — which gives this book its importance. This idea will endure even if everything else in the book should prove transient” (1903, in preface, vol. 1, p. ix).
How ironic that a man who so explicitly promoted the centrality of hierarchy should be remembered today primarily for his earlier advocacy of Allmacht at the traditional level of organismal struggle alone! A study of Weismann's intellectual ontogeny should lead us to respect the logic and power of hierarchy, whatever our [Page 224] eventual judgment about merit and utility. Weismann, by far the most thoughtful of Darwinians in the first generation after the founder himself, could not “cash out” the exclusivity of organismal selection when he pushed the theory to the edges of its necessary application. He then invented an auxiliary theory of suborganismal selection to rescue himself from an uncomfortable corner; but he eventually followed the relentless logic of his own argument to a full theory of hierarchy.
The theory of hierarchical selection does not constitute either a small and merely incremental nuance, or a modern concoction and exaggeration of bored Darwinians trying to stir up some trouble. Hierarchy has accompanied the theory of selection from its very inception — if only because no truly tenacious and thoughtful Darwinian could ever avoid its appeal and logic, while at least one of the wisest and the most committed adherents, August Weismann, came to regard hierarchy as the implied and necessary centerpiece of any evolutionary theory fully rooted in selectionist principles, and truly comprehensive in explanatory range. We have largely forgotten Weismann's intellectual journey today. But we should recover his chain of argument — for his motives and insights retain full validity, even if later discoveries about the physical basis of heredity invalidated his particular form of suborganismal selection.
Hints of Hierarchy in Supraorganismal Selection: Darwin on the Principle of Divergence
DIVERGENCE AND THE COMPLETION OF DARWIN'S SYSTEM
Charles Darwin cannot be judged as a consistently felicitous writer, but he could turn a phrase with the very best of craftsmen. As noted before, many of his lines, particularly his wonderful metaphors, have become parts of our culture — the image of the “entangled bank” at the very end of the Origin, or the “tree of life” that closes Chapter 4 on natural selection. His posthumously published autobiography contains many memorable and oft-quoted statements, including his descript
ion of intellectual eureka: “I can remember the very spot in the road, whilst in my carriage, when to my joy the solution occurred to me” (in F. Darwin, 1887, vol. 1, p. 84).
Poll our biological colleagues, and most will tell you that this horse-drawn epiphany describes Darwin's Malthusian insight of September 1838, and the resulting formulation of natural selection. But the passage refers to a much later event, and this error of attribution may be the most common in all Darwinian exegesis. The statement recounts an insight — the “principle of divergence” in his own description — that Darwin ranked as equal in importance with natural selection itself, an idea whose formulation sometime in the early to mid 1850's (the true date of the carriage ride) allowed him to complete his theoretical structure and begin writing his magnum opus.
Darwin describes the phenomenon that a principle of divergence must resolve, and states his surprise at his own obtuseness before the fateful carriage ride: [Page 225]
But at that time [after the Malthusian insight of 1838 and his composition of the sketches of 1842 and 1844] I overlooked one problem of great importance; and it is astonishing to me, except on the principle of Columbus and his egg,* how I could have overlooked it and its solution. The problem is the tendency in organic beings descended from the same stock to diverge in character as they become modified. That they have diverged greatly is obvious from the manner in which species of all kinds can be classed under genera, genera under families, families under suborders, and so forth (in F. Darwin, 1887, vol. 1, p. 84; the carriage statement directly follows).
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