Returning to the variations, which afford the material for . . . natural selection, we may distinguish two main kinds… Certain variations constantly occur, especially such as are connected with size, weight, color, etc. They are usually too small for natural selection to act upon, having hardly any influence in the struggle for life: others are more rare, occurring only from time to time, perhaps once or twice in a century, perhaps even only once in a thousand years. Moreover, these are of another type, not simply affecting size, number or weight, but bringing about something new, which may be useful or not. ... In his criticism of miscellaneous [Page 417] objections brought forward against the theory of natural selection after the publication of the first edition of the Origin of Species, Darwin stated his view on this point very clearly: — “The doctrine of natural selection or the survival of the fittest, which implies when variations or individual differences of a beneficial nature happen to arise, these will be preserved.” In this sense the words “happen to arise” appear to me of prominent significance. ... A distinction is indicated between ordinary fluctuations which are always present, and such variations as “happen to arise” from time to time. The latter afford the material for natural selection to act upon on the broad lines of organic development, but the first do not. Fortuitous variations are the species producing kind, which the theory requires; continuous fluctuations constitute, in this respect, a useless type... Darwin's variations, which from time to time happen to arise, are mutations, the opposite type being commonly designed fluctuations (de Vries, 1909b, pp. 70-72).
Seward responded in his unique footnote, and with annoyance barely concealed:
I think it right to point out that the interpretation of this passage from the Origin by Prof. De Vries is not accepted as correct either by Mr. Francis Darwin or by myself. We do not believe that Darwin intended to draw any distinction between two types of variation; the words 'when variations or individual differences of a beneficial nature happen to arise' are not in our opinion meant to imply a distinction between ordinary fluctuations and variations, which 'happen to arise.'... The statement in this passage that 'Darwin was well aware that ordinary variability has nothing to do with evolution, but that other kinds of variation were necessary' is contradicted by many passages in the Origin (Seward, 1909, p. 71).
Why did de Vries so covet a linkage with Darwin that he would torture and distort his hero's words to forge the supposed bond? And why did Seward single out this passage among others more overtly hostile to the source of this centennial celebration? To resolve this small puzzle, we must explore the wider context of de Vries' background and purposes. In particular, we must rescue de Vries from his conventional “sound bite” status as “Mendel's rediscoverer,” and recognize this near accident in his career as distinctly secondary to a much deeper, older, and direct inspiration from Darwin. We shall see that the profundity of de Vries' intellectual break with Darwin, combined with his psychological inability to sever overt homage, set the deeper source of Seward's legitimate annoyance about a single passage. An understanding of de Vries' reluctant apostasy provides our best biographically based insight into the nature of Darwinian logic — and of the persistent power and attraction of formalist alternatives (stressing the facet-flipping mode of Galton's polyhedron in this case). [Page 418]
The (not so contradictory) sources of the mutation theory
Hugo de Vries became the world's most celebrated evolutionist during the early 20th century. His Mutationstheorie received wide approbation as the most important proposal about evolutionary mechanisms since the Origin of Species and the theory of natural selection. He made three triumphant visits to the United States (in 1904, 1906, and 1912) and published two books in English (de Vries, 1905,1907a) based on summer lectures at the University of California, Berkeley. His views therefore became especially well known to American and other English-speaking audiences. All professionals continue to recognize his name today, but his ideas have suffered a nearly total eclipse for two major reasons, one legitimate and one unfair.
For the legitimate source, de Vries chose an unfortunate research strategy — a botanical equivalent of putting all his eggs in one basket. His theory — based largely on results from a single species, the evening primrose Oenothera Lamarckiana — requires that his chosen exemplar represent a biological norm in order to grant the required generality to his proposed mechanism. But the “species forming” saltations of Oenothera were soon revealed as oddities of an unusual chromosomal system, for Oenothera Lamarckiana is a permanent heterozygote, a hybrid with chromosomes of each component linked in rings, and thus segregating together in meiosis. (Only half the seeds are viable, because both homozygotes are lethal.)
For the unfair reason, de Vries has been so identified with an almost accidental moment of enduring fame that we have lost the main thrust and rationale of his life's work. Such moments often inspire catechistic one-liners that persist as the instant legacy of great thinkers. De Vries has suffered even more than most scholars caught in such a predicament, for he became the subject of two knee-jerk catechisms:
1. Mendel's forgotten work of 1865 was independently rediscovered in 1900 by Hugo de Vries, Carl Correns, and Erich Tschermak-Seysenegg.
2. Ironically, the first application of Mendelism to evolutionary theory did not help to affirm Darwinism, but to assert yet another alternative mechanism of change — the saltatory origin of new species by macromutation. The Modern Synthesis, the true fusion of Darwin and Mendel, began two decades later when scientists finally realized that small-scale (Darwinian) variation could also claim a particulate basis, and that macromutations played no important role in evolution. We may praise de Vries as a rediscoverer of Mendel, but his own interpretation of particulate inheritance delayed a proper resolution.
Neither of these conventional accounts can be dismissed as false, but neither properly expresses the reasons for de Vries' interests and discoveries. His link with Mendel represents a relatively minor encounter en passant in a career dedicated to other concerns. De Vries did discover the Mendelian segregation laws during the 1890's, and he did demonstrate their occurrence in some 20 species. As he prepared to publish this work in early 1900, his colleague, Professor Beyerinck at Delft, sent him an old paper with the following [Page 419] note: “I know that you are studying hybrids, so perhaps the enclosed reprint of the year 1865 by a certain Mendel, which I happen to possess, is still of some interest to you” (quoted in Stomps, 1954 — Stomps succeeded de Vries as professor of botany in Amsterdam). De Vries therefore reported Mendel's forgotten priority as he began to publish his results in 1900.
The link to Mendel, while surely true, must be labeled as unfair when cited as an exclusive epitome of de Vries' career. Discovery of the segregation laws did excite him, but this work represented only a sidelight to his major interest. Most early studies based on the Mendelian rediscovery did oppose Darwinism at first, but the deep irony of de Vries's contribution lies in the fact that he had taken up the study of heredity as a direct consequence of his concern — indeed, in his own words, his “love” — for Darwin as a man and a scholar. Darwin's theory of pangenesis (Darwin, 1868) served as de Vries' inspiration — and de Vries' first major book (his best in the judgment of many distinguished biologists, both then and now) presented a brilliant reformulation of Darwin's insight (Intracellular Pangenesis, de Vries, 1889).
De Vries turned to the study of heredity in order to probe the mechanisms of evolution. But he never considered the Mendelian segregation laws as particularly relevant to this goal — for these principles only regulated the distribution of characters by hybridization among differing phenotypes, whereas evolution required the origin of new variation. De Vries did not continue his work on Mendel's principles, and his two great books on evolution (de Vries, 1905 and 1909a) cite Mendel only rarely, and only in contexts peripheral to his main arguments about saltation and evolutionary novelty. De Vries's biog
rapher van der Pas rightly comments (1970, p. 99): “After the rediscovery of Mendel's laws, many investigators took up the subject. De Vries was not among them, however. He believed that hybridization only causes redistribution of existing characters and for that reason cannot explain the appearance of new species. Therefore, he concentrated on the phenomenon of mutation, which he believed explained the origin of new species and therefore gave necessary support to the theory of evolution.”
If Mendel only represented a sidelight in de Vries's career, two main sources stand out as inspirations for his interests and strategies — his teacher Julius Sachs and his mentor and guru Charles Darwin. De Vries' long life (1848-1935) spanned the years from Darwin to Dobzhansky. Unhappy with the quality of his initial botanical education in the Netherlands, de Vries decided, in the early 1870's, to continue his studies in Germany. Beginning in 1871, while teaching in an Amsterdam secondary school, de Vries began spending his long summer vacations in the laboratory of the leading plant physiologist, Julius Sachs. De Vries wrote a series of monographs and performed elegant experiments on osmosis in plant cells, the basis for his later work on the role of cellular turgor in the motions of growing plants. Sachs considered de Vries as his best student and helped to secure for him the first instructorship in plant physiology in the Netherlands, when the Amsterdam Athenaeum became a full university in 1877. De Vries later served as professor of botany [Page 420] and taught at Amsterdam until his retirement in 1918, though he remained professionally active until his death, working from an experimental garden and laboratory that he built in the remote village of Lunteren.
Through the 1870's, de Vries worked exclusively on problems in mechanical and chemical physiology. But, in the early 1880's, inspired directly by Darwin, he began to shift his interests to evolution and heredity. From 1885 to 1887, he published a series of 19 articles on “improving races of our cultivated plants” for a Dutch agricultural journal. He first found mutations of Oenothera in 1886, and worked steadily on his evolutionary views until his major work, Die Mutationstheorie appeared in two volumes in 1901 and 1903 (the Mendelian rediscovery only occurred as the book neared completion and could not have inspired much of de Vries' conceptual apparatus). De Vries credited his Intracellular Pangenesis of 1889 as the source of his theoretical views on evolution. By 1890, he had abandoned work in physiology, and he then spent the rest of his career as a student of evolution and heredity.
From Sachs and his colleagues, de Vries absorbed the leading philosophical tenets of late 19th century German science, then the envy and model of the Western world — experimentalism and the mechanical worldview. Throughout his later career in evolutionary biology, de Vries insisted that his success derived from his attempt to substitute an active, experimental and quantitative methodology for the older comparative and descriptive approaches of natural history.
In the frontispiece of his first American book (1905), de Vries shunned humility and ranked himself, by virtue of his experimentalism, at the pinnacle of progress in the history of evolutionary studies. (The Mutation Theory did not appear in English translation until 1909, and these published Berkeley lectures therefore represent the first extensive account of de Vries' views in English. Intracellular Pangenesis first appeared in English translation in 1910.) De Vries wrote:
The origin of species is a natural phenomenon — Lamarck.
The origin of species is an object of inquiry — Darwin.
The origin of species is an object of experimental investigation — de Vries (1905, frontispiece).
De Vries' rhetorical expression of this theme in his major work (1909a translation of 1901 German edition) follows an interesting course — self-serving to be sure, but revealing. Failure to progress in evolutionary studies, he argues, may be attributed to an antiquated methodology: “We have a doctrine of descent resting on a morphological foundation. The time has come to erect one on an experimental basis” (1909a, volume 1, p. 207). (De Vries maintained a generous view of the experimental domain — for he usually applied the term to the rigorous recording of well-tracked pedigrees in garden plots, rather than to more classical manipulation in sterilized buildings under controlled conditions. He wrote (1905, p. 463): “The exact methods of the laboratory must be used, and in this case the garden is the laboratory.”)
De Vries then extended his argument in two directions from this central [Page 421] methodological premise. First, to gain broadest generality in aligning evolutionary studies with physical sciences of higher status, de Vries opens The Mutation Theory with a claim that theories based on discrete, atomized particles suggest better experiments than hypotheses about continua. Moreover, such theories can also ally biology with more prestigious fields like chemistry: “By the mutation theory I mean the proposition that the attributes of organisms consist of distinct, separate and independent units. These units can be associated in groups and we find, in allied species, the same units and groups of units. Transitions, such as we so frequently meet with in the external form, both of animals and plants, are as completely absent between these units as they are between the molecules of the chemist” (1909a, volume 1, p. 3). He then expressed the same argument more strongly in a popular article (1907b, p. 17): “This principle of mutations is conducive to the assumption of distinct units in the characters of plants and animals. Even as chemistry has reached its present high development chiefly through the assumption of atoms and molecules as definite units, the qualities of which would be measurable and could be expressed in figures, in the same way systematic botany and the allied comparative studies are in need of a basis for measurement and calculations.”
Second, and in an odd conflation of proper methodology and empirical truth-value, de Vries argues in his Preface that Darwinian gradualism should be rejected (or at least strongly disfavored a priori) because insensible change over millennia cannot easily become the subject of experiment!
The origin of species has so far been the object of comparative studies only. It is generally believed that this highly important phenomenon does not lend itself to direct observation, and, much less, to experimental investigation. This belief has its root in the prevalent form of the conception of species and in the opinion that the species of animals and plants have originated by imperceptible gradations. These changes are indeed believed to be so slow that the life of a man is not long enough to enable him to witness the origin of a new form. The object of the present book is to show that species arise by saltations and that the individual saltations are occurrences which can be observed like any other physiological process ... In this way we may hope to realize the possibility of elucidating, by experiment, the laws to which the origin of new species conform (1909a, volume 1, p. vii).
With such negativity towards the methodology and worldview of natural selection and gradualism, how could Charles Darwin serve de Vries as chief intellectual guru, even surpassing the influence of Sachs and experimental-ism? We cannot grasp de Vries' convictions and contradictions until we understand the powerful extent and threefold nature of Darwin's largely psychological hold upon him.
First of all, we often forget the extent of Darwin's work on plant physiology — largely published during the 1870's as de Vries began his career, and primarily in the same areas, particularly the proximate causes of movement, [Page 422] that most interested de Vries. Darwin wrote books on Insectivorous Plants (1875a), The Movement and Habits of Climbing Plants (1875b), and The Power of Movement in Plants (1880a). In these technical studies, the two men could not have stood closer as intellectual colleagues — even though their enduring fame would arise elsewhere, from their disparate studies of evolution.
Second, de Vries directly courted and won Darwin's admiration and friendship. The two men exchanged extensive correspondence (reprinted in Van der Pas, 1970). Darwin extended much effort to help de Vries. He sent complimentary copies of his books to de Vries, and he wrote to Asa Gray for seeds, so that de Vries cou
ld pursue some experiments on movement in tendrils. De Vries, for his part, repeated and extended many of Darwin's experiments on the physiological basis of movement and insectivory in several species. For example, de Vries wrote to Darwin on December 8, 1880:
I am very much obliged to you for your great kindness of sending me your work on the Power of Movement in Plants ... I was especially interested by your experiments on the movements and the curious sensitiveness of the roots and plumules of young seedling plants, which I hope to repeat as soon as I shall have an occasion ... I always remember the great pleasure I had in repeating the experiments, described in your work on insectivorous plants.... In your work, you often speak of my papers, . . . and I am much indebted to you for your kind judgment of them, which will be a stimulus to me in endeavoring to contribute my part to the advancement of science.
In the summer of 1878, just before promotion to his Amsterdam professorship, de Vries visited England and fulfilled his fondest hope of meeting Darwin. He first called on Hooker and Thistleton-Dyer in London, but found them cool, however kind and correct. By contrast, de Vries greatly enjoyed a memorable, if short, visit with Darwin at Dorking, the home of Darwin's brother-in-law, Sir Thomas H. Farrer. De Vries described this visit in a charming letter to his fiancee on August 14, 1878:
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