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  • 1. 1 ‘In Weismann’s Footsteps: The Cyto-rebellion of C.D. Darlington’ Oren Harman Introduction “The time in which men believed that science could be advanced by the mere collection of facts has long passed away.”1 Such was the judgment of the ageing, increasingly cantankerous August Weismann, Germany’s leading biologist, in 1886. A short four years after the death of Charles Darwin, Weismann was intent on describing a cellular theory to match the English naturalist’s theory of evolution by natural selection. “The investigation of mere details,” he wrote, “had led to a state of intellectual short-sightedness, interest being shown only for that which was immediately in view. Immense numbers of detailed facts were thus accumulated, but… the intellectual bond which should have bound them together was wanting.”2 What biology needed more than anything was a stroke of bold theory-making, and that’s what Weismann delivered: for sexual organisms to beget offspring, there must exist a special reduction division, otherwise the genetic material would double in each successive generation.3 Not that Weismann, who was increasingly growing blind, or anyone else for that matter, had actually seen this division occur. This leap of faith was based entirely on unassailable genetic logic, and it gave meiosis – a term coined in 1905 – to the world. It would also render Weismann a hero to a young English cytologist struggling to figure our what precisely happens during meiosis, some forty years into the future. We’ll return to Weismann later, but first, let’s leap ahead in time to the real subject of our story. 1
  • 2. 2 Cyril Dean Darlington (1903-1981) was born by mistake. “My birth gave rise to a crisis in the family,” he wrote years later. “My mother claimed that she didn’t know how it happened. My father on the contrary was quite certain. He applied a rule without formally declaring it that never again would he cohabit with his wife. It was a rule that he never broke in his remaining forty years. Whether he regarded me as an accessory to this mishap or misdemeanor I am still not sure.”4 Here, at the very beginning, was planted the seed of all that was to come. Darlington’s very existence was from the outset shrouded in doubt. It was far from clear that he was even wanted. Darlington would show the world, and, especially, his father, that the ‘mishap’ or ‘misdemeanor’ had not been in vain. Darlington was born a rebel. Alfred, his lone and older brother, was always his father’s favorite. Away from their Lancashire, and then Ealing, home, fighting the war against the Germans and winning medals of honor, Alfred’s very existence seemed to accentuate Cyril’s own uselessness at home. Invariably, he caught the wrath of his dyspeptic father. Mother was overprotective, and increasingly depressed. Childhood was a sullen, hollow affair. When he finally graduated from the South Eastern Agricultural College at Wye, Darlington put in an application for a scholarship to travel abroad, as far away as possible- to Trinidad, to become a farmer. A tough and cocky outer veneer had come to characterize his dealings with people. Already he was anti-authoritarian in the extreme, writing to his father at eighteen: “…nothing galls me so much as to have other people’s beliefs forced down my throat.”5 But showing no signs of its author being either a promising student or a terribly talented agriculturalist, Darlington’s Caribbean application was rejected by the Empire Cotton Growing Corporation. Disaffected, arrogant, and at wits end, Darlington was cajoled by a master at Wye to 2
  • 3. 3 try the next (and only) best thing: a volunteer position at the John Innes Horticultural Institution. After all, the only subject that had captured Darlington’s imagination at Wye had been the new field people were now calling ‘genetics.’ The Innes was Britain’s premier horticultural institute, but its Governing Council was able to secure the famous Mendelian William Bateson as its first director in 1910 only by promising to allow research on genetics as well. “The rewards from genetics are slight,” the white-haired Bateson pronounced beneath his moustache as he approached a cocky but frightened Darlington in his carpet slippers in the Institution’s library in the fall of 1923, “only those who attained unheard of heights of achievement can ever hope to make a living out of it.”6 Uncertain of his direction, but determined nevertheless to succeed at all costs, Darlington shook the old man’s hand. “Unheard of heights of achievement” somehow sounded strangely alluring. Although he didn’t know it, by the time Darlington had arrived at the Innes the once pioneering Bateson was an ageing director, already surpassed by Thomas Hunt Morgan and his ‘Fly Room’ group at Columbia University across the Atlantic in New York. The chromosomal theory of heredity, which postulated that the genes responsible for heredity lay physically on the chromosomes in the nucleus of cells, was the lynchpin upon which the success of Morgan’s genetics lay. But Bateson, a philosophical aesthete who had little time for materialism, denied the role of the chromosomes in the hereditary process.7 Stubborn yet realistic, Bateson had journeyed in the winter of 1921-1922 to the United States to see for himself what the chromosome theory had to offer genetics after all. Impressed and profoundly humbled he appointed upon return a cytologist, Frank Newton, less as an omen of a complete 3
  • 4. 4 change of mind and more as a fig leaf to cover what looked to be, in the new world of chromosomal genetics, an embarrassment. Newton was skeptical of Bateson, and, when Darlington arrived, took him under his wing, teaching him how to examine hyacinth chromosomes under the old brass microscope his boss had begrudgingly supplied him. By 1926 Bateson was dead, and Newton, just 33, succumbed to cancer less than a year after the Director. Left literally to his own vices and devices, the young Darlington – outwardly overconfident, but really disguising a deep sense of awe at a mysterious microscopic world entirely unknown to him, and seemingly very illusive - set out to make his own sense of the chromosomes and their role in nature. He was now a rebel with a field if not yet a cause, no matter how at sea or ill-prepared for the fight. “At the age of 18 most of the world seemed stupid and annoyed me,” he informed his Diary, “at 24 I know it is stupid and it ceases to worry me.”8 The outrageous confidence would prove valuable. Within five short years, and working almost entirely alone, Darlington authored Recent Advances in Cytology in 1932, a book that was to have a profound impact not only on his own field of cytology, but on genetics, and evolutionary theory as well, catapulting Darlington to world fame. It would also fashion him one of the greatest rebels cytology had ever seen. Recent Advances in Cytology So what was the nature of Darlington’s rebellion? And what was he rebelling against? When Darlington turned as an orphaned scientist to look upon the chromosomes, two problems continued to dominate the silent world of cytology inhabiting the space between the ocular lens above and the preparation slide below. First, did the chromosomes pair side-by-side during reduction division (meiosis), or was it end-to- 4
  • 5. 5 end? This was important, for if the chromosomes paired end-to-end, it would be unclear how they exchanged genetic material between them. The exchange of genetic material between homologous chromosomes, called crossing over, was presumed to happen during meiosis, and seemed to be the explanation for much of the variation begot by each successive generation in nature, and the true benefit of sexuality. In 1909 the Belgian cytologist and Jesuit priest Frans Alfons Janssens had observed cross-like figures produced by the tangled homologous chromosomes during meiosis, and called them chiasmata, meaning cross-like. Morgan assumed that Janssens’ chiasmata evidenced the physical crossing over of genes between maternal and paternal chromosomes, and turned this assumption (it had yet to be proven) into the very crux of the mapping procedure he and his group developed to suggest that genes lay physically on the chromosomes. It’s preoccupations small and technical, the second problem vexing cytology was whether the chiasmata were the result, or rather the cause of such crossing-over. Working almost entirely in isolation, Darlington was able within a few short years to produce an axiomatic account of chromosome mechanics. In three simple laws he summed up the entire system: (1) All attraction between chromosomes is always in pairs, and side-by-side, as opposed to end-to-end; (2) Chiasmata are the condition of orderly pairing and later segregation during meiosis; (3) Chiasmata are always the consequence of genetic crossing over between homologous chromosomes. Why was any of this important? Peering through the lens of a microscope at the tiny world of the chromosomes, it was the grander questions of an evolutionary nature that Darlington was really after. Only after the laws of chromosome mechanics were described and understood could their role in evolution be theorized. In the preface to Recent Advances in Cytology, 5
  • 6. 6 Darlington made clear where all this was leading: The importance of the chromosome as determining the hereditary functions has placed them outside the ordinary field of evolutionary enquiry. They have been considered as the very fount and origin of adaptive change and therefore not themselves capable of adaptation. Now they can be shown to be subject to the genetical variation which they themselves, by changes of their parts, determine.9 In the final chapter, ‘The Evolution of Genetic Systems,’ Darlington outlined these ideas in full force. Not only did heredity lead to evolution, he argued; heredity itself was subject to evolution. Morgan and company had shown that genes exist on chromosomes, like beads on a string, and that they somehow carry the secrets of heredity. Following this lead, the mathematical population geneticists demonstrated with little more than pen and pencil that evolution works by nature selecting those genes that are adaptive and selecting out those genes that are not. Darlington was now arguing that the chromosomes, far from passive repositories of genes, are themselves under genetic control, and determine by their movements the relative amount and kind of recombination of genes occurring in each successive generation. It was this quantity – the amount and kind of variation produced during meiosis upon which selection can act – which more than any other variable determined the fate of organisms and ultimately the origin and propagation of species. Having begun five years earlier by looking at chromosomes for their own sake, Darlington could now begin to understand evolution itself largely as a function of their behavior. Reception Making cytology relevant to evolution would seem to be a welcome development, but Darlington’s ideas quickly met unbridled reactions of scorn and indignation. 6
  • 7. 7 Hampton Carson, a young graduate student at the time, remembered the reaction to Recent Advances of Cytology in his biology department at the University of Pennsylvania: “The older members of this strongly cytological department received the Darlington book with stiff attitudes of outrage, anger, and ridicule. The book was considered to be dangerous, in fact poisonous, for the minds of graduate students… Those of us who had copies kept them in a drawer rather than on the tops of our desks.”10 At the Sixth International Congress of Genetics at Ithaca in the winter of 1932, Darlington was given just five minutes to defend his views, and was shouted down by a storm of critics. On the West Coast, the leading American cytologist, John Belling, was working zealously on a scathing ‘Critical Review.’ A Canadian colleague, Charles Leonard Huskins, offered to come across the Atlantic to punch Darlington’s head off! In the relatively tranquil world of chromosomes, Darlington had done something to make a lot of people very mad. So what was all the raucous about? To be sure, there were factual and experiment claims made by Darlington that fellow cytologists challenged. In a science notorious for its intrinsic slipperiness - a “strange and difficult kind of visual chemistry with rules only dimly perceived” as one practitioner called it -11 little could be legitimately claimed which was not immediately obvious to the visual sense. Darlington set down sweeping laws for much that was not visually obvious. Yet almost all the initial reservations to Darlington’s supporting observations of the behavior of chromosomes (principally the number and frequency of chiasmata) were taken back one by one, as chromosomal work in the early thirties tended to support his axiomatic claims. The initial factual shock his book elicited within cytology ultimately gave way to acceptance, and by 1939 Sturtevant and Beadle, in their standard text An Introduction to Genetics, spoke 7
  • 8. 8 of it as marking “the unification of chromosome cytology.”12 If Darlington’s microscopy was not the issue, than what was? Why was he being so vigorously resisted? Though not particularly quantitative himself, Darlington’s chromosome-centered genetic system introduced too many dimensions for the mathematical population geneticist to cope with. The gene was a one-dimensional variable. Whether or not Wright, Haldane, and Fisher took them to be so, their paper and pencil models were major oversimplifications. It was impossible for them to cope with all the effects of selection when the mechanism controlling selection (chromosome behavior during meiosis) and the unit that is being selected (the gene) are themselves both being changed by selection. Unlike the gene in the mathematical population geneticist’s scheme, Darlington’s chromosome-centered genetic system had no single dynamic focus. It integrated several interacting variables: the shape of the chromosomes, their number, the life cycles of organisms, their reproductive organisations and their breeding behavior (outbreeding or inbreeding, sexually differentiated or hermaphrodite). All these were related in a system whose parts are mutually adapted and adaptively connected. Years later the Harvard systematist and ornithologist Ernst Mayr wrote to Darlington: “Your thinking simply did not fit into the atmosphere of what I have dubbed ‘beanbag genetics.’”13 To be sure, Fisher realised that the hereditary mechanism itself could evolve under pressure of selection. In his 1932 address to the Genetics Congress at Ithaca, Fisher offered: “Others have considered the bearing of the theory of heredity on evolution. I am going to consider the bearing of evolution on heredity.” 14 His paper “Evolutionary Modification of Genetic Phenomena” reversed the accepted order manifested in Haldane’s address, entitled “Can Evolution Be Explained In Terms of 8
  • 9. 9 Present Known Genetical Causes?”15 But the level at which Fisher posed the question - the gene level - was different from Darlington’s - that of the behavior of whole chromosomes. Fisher was unaware at Ithaca that Darlington had just published an account arriving at the same principal conclusion of the relevance of evolution to heredity, but when confronted by the young man with the notion of dynamic genetic systems he “never appeared to hear.”16 Haldane was personally closer to Darlington, having acted as something of a mentor during the time he spent at the John Innes as head of genetical research beginning in the spring of 1927. Haldane understood that the bell attached to Darlington’s perspective must ring true in nature: the primary result of chromosome-centered genetic systems is the generation, preservation and recombination of differences upon which natural selection acts in furthering evolutionary change.17 Even if theoretical models could not yet be constructed to describe the full implications of the chromosome-centered genetic system for evolution in quantified terms, it was clear that such chromosomal phenomena as inversions, recombination, polyploidy, balanced lethals and ring-formation collectively play a more important role than simple point mutations, even if they constitute merely shuffling of already existing genetic materials instead of creating entirely new ones. Evolutionary-minded geneticists had put all the focus on genes and mutations. Darlington now made it clear that chromosome mechanics play an even more important role. Once again, Mayr summed it up: “…no one made a greater contribution to the understanding of recombination and its evolutionary importance than Darlington.”18 The conceptual difficulties presented by Darlington’s scheme, much the same as the initial attempts to challenge his microscopy, fail to explain the harsh reaction against his ideas. Adjectives like ‘dangerous’ and ‘poisonous’ in science are reserved 9
  • 10. 10 for more than mere unusual theories. They usually rear their ugly head against what the established community of researchers dub as scientific rebellions, full-on challenges to orthodox wisdom, meaning daring confrontations that must, at all costs, be put down, or else! What then can account for the unusual roughness with which Darlington, the young and brash scientific upstart, was treated? What was he rebelling against? Method In the winter of 1932, John Belling at Berkeley was engaged in preparing a scathing attack on Recent Advances in Cytology. Belling died of heart disease at the end of February, and in May of that year, ‘Critical Notes on Darlington’s Recent Advances in Cytology’ appeared posthumously. “The method of the author,” Belling wrote, is to try to establish general propositions, and then to deduce from these. Unfortunately, to a general proposition there are sometimes enough exceptions to invalidate it… Darlington’s book contains too many conjectures.19 Referring to Darlington’s writing as ‘propaganda,’ America’s leading cytologist suggested that Darlington cut out nine tenths of his conjectures in the second edition. Propaganda?! Darlington was unshaken. It seemed apparent to him that the distinction between fact and theory (especially in cytology) was useless, or only useful so long as it was remembered that it was arbitrary. In a reply to Belling he offered a forceful justification of his method: Belling maintains the morphological point of view, of which he is the ablest exponent. I maintain the analytical point of view, namely: every student should be aware of the conjectures that may reasonably be made in regard to 10
  • 11. 11 the causes of the events he is studying. I maintain it partly, perhaps, because to me the cause is more real than the event itself.20 (emphasis added). *** Darlington was now in America, a twenty nine year old Rockefeller Fellow for the 1932-1933 academic year, hopping between labs on the East and West coasts. On a visit to Woods Hole (where he met Morgan and E.B. Wilson among others), a young lady approached him after a talk and offered that they marry. Darlington knew that such impetuousness would gravely hurt his parents, and seemed to revel in the thought. “Promiscuity only flourished under condemnation,” he noted blithely in his Diary. To his socially conservative parents, who wrote frantic letters in an attempt to dissuade their rebellious son from tying the knot (“have you lost all your moral sense? My dear boy, think a good deal of what you are doing before it is too late!… Father has no respect left for you, and I am made to feel it. Your loving and affectionate mother…”), Darlington chose to drive the taunt even further: “…We bathed in the son entirely in the nude and got a little sunburned,” he wrote, no doubt relishing the moment. Finally, miffed, he barked: “I wonder whether you will ever learn not to expect your son to behave the same way as your next door neighbor’s sons!”.21 The marriage (surprise, surprise!) lasted only a few months, but Darlington had already set himself on his course. He was self-consciously fashioning himself a rebel on all fronts. “Those who obey a general moral code,” he told his Diary, “will always resent those who adopt an independent and changeable one… Vox populi is always vox diaboli.”22 What was true for the bedroom, was true for the preparation slide. When Belling attacked Darlington, he was representing an entire school of inductive, cautious cytology now under threat from a young, gun-slinging deductive upstart. Self-taught 11
  • 12. 12 and arrogant, Darlington took pleasure in bucking the old-schoolers. He found they’re patience tiring, their focus on technical problems barren, and their caution sterile. “I always want to preach what I practice,” Darlington now wrote in his Diary, “a dangerous course for a rebel.” But if the icon of careful induction had been Darlington’s target, why, still, was the reaction against him so strong? What was it about that disciplinary landscape of biology that rendered Darlington’s methodological rebellion ‘poisonous’ to young minds? The Disciplinary Landscape The history of cytology falls rather naturally into quarter-centuries, beginning with Oscar Hertwig’s discovery of fertilisation in 1875. From then until 1900, the mitotic apparatus, the chromosomes, gamete formation, and early embryology were all defined and recognised. It was an exciting period, the atmosphere charged with the conviction that science was on the verge of uncovering the secrets of the life processes and perhaps life itself. It was clear that cytology represented an independent field of research at the forefront of progress in biology. When Mendel’s laws were re-discovered at the turn of the century, cytology and genetics stood on almost equal footing as far as the new study of heredity was concerned. The Sutton-Boveri hypothesis of 1902 showed that chromosomes in the nucleus of cells and traits expressed in the bodies of organisms were two sides of the same coin, and cytology and genetics were the two handmaidens leading biology towards the unlocking of the secrets of heredity. Before long, a close co-operation between cytologists and geneticists gave birth to the chromosomal theory of heredity. And yet Janssens’ chiasmatype theory of 1909 marked the beginning of a trend that 12
  • 13. 13 was to re-define the role of cytology for the generation ahead. For when Morgan took up the notion that the observed chiasmata were in fact the locus of genetic crossing over, the statistically based breeding and mapping work of the geneticists suddenly became emancipated. As a divide between describers and experimenters increasingly bifurcated biology, willy-nilly cytology came to play the secondary role of supporter. Soon, cytologists’ virtue came to lay in their utter reliability. Proceeding with extreme caution, they would no longer make claims unless they could be verified by increasingly stricter standards of empirical proof. This environment quickly engendered theoretical sterility fostered by an acceptance of Bateson’s exhortation to ‘treasure your exceptions,’ and these soon amounted to hundreds of papers littered about the cytological literature. A comparison of E. B. Wilson’s First and Third editions of The Cell proves the point. Wilson’s 1896 book was a highly speculative, and bold account of cytological knowledge on the eve of Mendel’s re-discovery. Twenty-nine years later, however, any sign of speculation had vanished without a trace, and the initial 371-page deductive treatise had been replaced by a 1,232 page inductive collection of disintegrated observation. Wilson’s Third Edition, replete with its hedging and prevarications on the laws of pairing and crossing over, was precisely what Weismann had been speaking of forty years earlier when he described the immense number of detailed facts accumulated, for which “the intellectual bond which should have bound them together was wanting.” From a pioneer, the cytologist had become a doubting Thomas, and, in contrast to the budding geneticist, seemed to be doing little to help the cause along. Arriving on the scene just shortly after the appearance of Wilson’s book in 1925 Darlington immediately recognised his own situation reflected in that of his hero 13
  • 14. 14 Weismann. Remembering Darwin’s own exhortation – “I can have no doubt that speculative men, with a curb on make far the best observers”23 -Darlington, like Weismann before him, felt that in an age of empiricism it was important that someone have the courage to speculate. Darlington’s disposition, like Weismann’s, was theoretical, despite working in a highly detailed, descriptive field. Like Weismann, Darlington was not afraid to advance conjectures unsupported by observation, but rather deduced from genetic assumptions. Finally, like him, Darlington was really using cytology as a tool with which to probe the problems of greatest interest to him - those of evolution. The referrentiality was intentional: Almost every Darlington paper after 1931 quoted Weismann’s great speculation of reduction division made in 1887, implicitly drawing the connection to his own (Darlington’s) bold speculations. When Darlington grasped that cytology needed to be emancipated and made relevant once more, he turned from a mere rebel with a field to a rebel with a cause; Recent Advances in Cytology was his manifesto. Haldane gave expression to this rebellious revolution, calling his young colleague’s research “the beginning of a new epoch, the transition from an essentially descriptive to a largely deductive science.”24 Old school cytologists like Belling were not nearly as pleased. To them, Darlington’s new type of bold, deductive, and often conjectural hypothesis-making represented a threat to their scientific autonomy and credentials. Cytology after all, had come to be defined by its cautious, meticulous, ‘show-me’ style. Anything else was plain and simple not cytology, it wasn’t even science! If caution were thrown to the wind, and faltered, what honor would remain in the profession? How would cytologists ever again be trusted? By breaking the hold of the old inductive method, Darlington shifted cytology in the biological landscape of his day in relation to genetics and evolutionary theory. 14
  • 15. 15 Cytologists could once again ask big questions about the origin of species and the evolution of taxonomical lines, rather then slinking deeper and deeper into the increasingly technical and unintelligible language of ‘karyokinesis’, ‘heterotypic’, and the ins and outs of ‘Acidic-Lacmoid Squash’ methods. And where cytology could once again dare, as in the days of Weismann, biology was sure to gain. Nowhere was this more apparent than in what became known as ‘the evolutionary synthesis.’ The great catalyst of this enterprise was the Russian-born American geneticist Theodosius Dobzhansky’s 1937 book Genetics and the Origin of Species, the first coherent work to link the ‘dry’ theories of the mathematical geneticists to natural populations in the wild. In a series of experiments charting seasonal and yearly morphological and genetic changes in the chromosomes of natural populations of Drosophila (inversions, recombinations), Dobzhansky had shown how cytological changes could be selected and influence the evolution of a population. Dobzhansky relied heavily on Darlington’s work, citing him more than any other researcher beside Sturtevant and Sewall Wright. Never mind that Darlington would be afforded little credit for his role in the synthesis.25 What counted was that Dobzhansky’s book was immensely successful in placing the chromosome at the heart of evolution.26 This had been Darlington’s aim all along, but he was a cytologist. What business did he have tackling evolution?! Only after Dobzhansky made it legitimate to consider chromosome behavior in relation to evolution could Darlington’s original ideas be slowly understood and incorporated into the mainstream. Cytogenetics, the science Darlington in no small measure helped resurrect in the 1930s, had ultimately become, through Dobzhansky, an important catalyst of the evolutionary synthesis, arguably the greatest intellectual achievement in biology since Darwin. By blazing a new and boldly deductive methodological path, Darlington succeeded in breaking down long- 15
  • 16. 16 preserved boundaries between the different disciplines of the life sciences. Weismann would have been proud. Epilogue Applying chromosome mechanics to evolutionary theory, Darlington had made bold and grand speculation the very totem of his science. Method, first and foremost, was the stuff of his rebellion. Many of Darlington’s bold speculations on chromosome mechanics would eventually have to be revisited, even overturned.27 And while rebellions of any kind invariably exact a price, truth, as Francis Bacon intoned, really does sometimes emerge more readily from error than from confusion. Thus, the general perspective on the importance of chromosome mechanics in evolution would remain, even if it’s complex details have yet to be worked out even today.28 Darlington’s iconoclasm is important for the history of biology because it happened just as the legacies of the two greatest biologists of the 19th century – Darwin and Mendel – were finally being wed to each other, setting the scene for a picture of life that has remained with us, notwithstanding a poke here and there, until this very day. Studying Darlington’s life, one gets the feeling that nothing but unhindered iconoclasm would satisfy this Lancashire lad’s need to justify his own existence. When following his revolution cytology slowly returned to a more inductive, cautious style, towards the mid forties Darlington turned to cytoplasmic inheritance, once again exciting ire and controversy. In the fifties and sixties he turned to man, applying the determinism he had witnessed in the dance of chromosomes under the microscope to human history and culture, sparking even greater controversy still. “The most important knowledge of any time is the knowledge whose truth is disputed,” he shared with his trusted Diary. “No subject keeps my interest when I find my own view of it 16
  • 17. 17 agrees with the accepted or majority view.”29 Spoken like a true rebel! Darlington was a biologist of great intuition, but often of less than responsible practice. He sometimes made daring claims based on little empirical evidence, even if rooted in solid theoretical ground. Like Weismann before him, he practiced and took pleasure in the art of the considered guess. What can we learn from his experience? Perhaps the most important lesson is this: Science always needs both Promethean theoretical leaps, and ant-like, blow-whistle, painstaking drudgery. At certain times, an emphasis on the one may come at the expense of the other, but this is not always a bad thing. In the end, the success of Darlington’s rebellion in cytology meant that a stultified field could once again be made to thrive. That his empirics were reigned in by the next generation of cytologists simply goes to show what Darlington himself always believed to be true about his trade. “Science advances as though by the pulling out of a drawer which gives on one side only to jam on the other… There is nothing to be gained except by pulling on the other side.”30 The blind August Weismann, one of the greatest cabinet-makers biology has ever known, would no doubt wink to that. 17
  • 18. 1 Weismann, Die Bedeutung der sexuellen Fortpflanzung für die Selektionstheorie (Jena: Gustav Fisher, 1886), p. 295. 2 Weismann, Studies in the Theory of descent, R. Mendola trans. And ed., (New York: AMS Press, 1975), p. xv. 3 Weismann, August. 1887. “On the Significance of the Polar Globules,” Nature 36: 607-9. 4 Autobiographical notes, 14 November 1977, the Darlington Papers (DP):C.1:A.3 5 Darlington letter to his father, DP:C.5:A.169 (1922). 6 Taped Darlington interview with Brian Harrison (25 July 19759), John Innes Horticultural Collection, The John Innes Institute, Norwich; DP:C.88:f.82. 7 Coleman, 1970. 8 Diary, 1927, DP:g.32:A.65. 9 Darlington, 1932, p. viii. 10 Carson, in Mayr and Provine, 1998, p. 91. 11 Carson, in Mayr and Provine, p. 89. 12 Sturtevant, A.H. and Beadle, G.W., An Introduction to Genetics (Philadelphia: W.B. Saunders, 1939), p. 364. 13 Mayr letter to Darlington (13.5.1974), DP:C.104:H.160. 14 Apparently, Fisher’s aphoristic style was an improvement on what appears in print. This quote is from Darlington, in Mayr and Provine, 1998, p. 74. 15 See Proceedings of the Sixth International Congress in Genetics, 1932 (Menasha:WI: Brooklyn Botanic Garden, 1932), pp. 165-172, and 185-189. 16 Darlington, in Mayr and Provine, p. 79. 17 See Haldane’s preface to Darlington, 1932, p. vi. 18 Mayr and Provine, p. 23. 19 Belling, J., “Critical Notes on Darlington’s Recent Advances in Cytology,” University of Californai Publications in Botany, 17, no. 3 (1933), quote on p. 76. 20 “Reply by C.D. Darlington,” in Belling, op. cit., p. 110. 21 Darlington letters to parents, August 1932, DP:C.6:A.184-190; Diary, DP:A.70:f.11. 22 Diary, 1930’s. not all dated, DP:g.33:A:66-70. 23 Charles Darwin letter to Charles Henry Lardner Woodd, 24 February, 1950, in F. Burkhardt and S. Smith eds., The Correspondence of Charles Darwin, vol.4 (Cambridge: Cambridge University Press, 1985-91), pp. 317 24 Darlington, 1932, p. v.
  • 19. 25 Darlington was cited 14 times in Dobzhansky’s 1937 book. Moreover, Chapter 4, ‘Chromosomal Changes,’ was 50 pages long and the centerpiece of the work. Nevertheless, Darlington is almost never mentioned as an important player in the evolutionary synthesis literature. The exception is Mayr and Provine, and even here Provine states in the epilogue: “The role of cytologists is especially difficult to assess. They seem to have played no major role in the synthesis.” (1998,. p. 408). This is significant, for elsewhere he calls Darlington’s Evolution of Genetic Systems “enormously influential” (p. 70), meaning that his contribution is not understood as coming from cytology. 26 An immediate effect was the birth of a major branch of Drosophila work dealing with cytogenetics, evolution, and natural populations, pioneered at Texas. 27 The universal law of pairing two-by-two ceased to be thought of as universal. Chromosomes do often pair in threes and in fours, and evolution has found ways to safeguard orderly segregation nonetheless. Indeed, although not yet entirely understood or explained, it became apparent that other mechanisms besides chiasmata were playing important roles in keeping chromosomes paired in meiosis, and hence in their orderly segregation for gamete formation. 28 While technical advances are pushing cytogenetics to greater heights (see Michael R. Speicher and Nigel P. Carter, “The New Cytogenetics: blurring the boundaries with molecular biology,” Nature Reviews Genetics, vol. 6, no. 10, 2005, pp. 782-792), fundamental problems such as achiasmatypy in the male fly, the mechanism by which homologous chromosomes find each other for pairing, and a thorough understanding of the effects of all chromosome changes on the evolution of natural populations, remain elusive. 29 Diary entries, 1930s, not all dated, DP:g.33:A:66-70; DP:e.11:A.82 (1962) 30 Darlington, The Conflict of Science and Society (London: Watts and Co., 1949), p. 6. Bibliography: Coleman, William, “Bateson and the Chromosomes: Conservative Thought in Science,” Centaurus, 15 (1970), pp. 228-314. Darlington, Cyril Dean, Recent Advances in Cytology (London: Churchill, 1932) Darlington, Cyril Dean, The Evolution of Genetic Systems (Cambridge: Cambridge University Press, 1939) Harman, Oren Solomon, The Man Who Invented the Chromosome: A Life of Cyril Darlington (Cambridge, Mass: Harvard University Press, 2004) Hughes, Arthur, A History of Cytology (London, Abelard-Schuman, 1959)
  • 20. Mayr, Ernst and Provine, William B., eds., The Evolutionary Synthesis: Perspectives on the Unification of Biology (Cambridge, Mass: Harvard University Press, 1998).